Database.Esqueleto.Internal.Internal

This is an internal module, anything exported by this module may change without a major version bump. Please use only Database.Esqueleto if possible.

If you use this module, please report what your use case is on the issue tracker so we can safely support it.

Documentation

fromStart :: forall a. (PersistEntity a, BackendCompatible SqlBackend (PersistEntityBackend a)) => SqlQuery (PreprocessedFrom (SqlExpr (Entity a)))

(Internal) Start a from query with an entity. from does two kinds of magic using fromStart, fromJoin and fromFinish:

1. The simple but tedious magic of allowing tuples to be used.
2. The more advanced magic of creating JOINs. The JOIN is processed from right to left. The rightmost entity of the JOIN is created with fromStart. Each JOIN step is then translated into a call to fromJoin. In the end, fromFinish is called to materialize the JOIN.

newtype DBName

Copied from persistent

Constructors

DBName

Fields

• unDBName :: Text

fromStartMaybe :: (PersistEntity a, BackendCompatible SqlBackend (PersistEntityBackend a)) => SqlQuery (PreprocessedFrom (SqlExpr (Maybe (Entity a))))

(Internal) Same as fromStart, but entity may be missing.

fromJoin :: IsJoinKind join => PreprocessedFrom a -> PreprocessedFrom b -> SqlQuery (PreprocessedFrom (join a b))

(Internal) Do a JOIN.

fromFinish :: PreprocessedFrom a -> SqlQuery a

(Internal) Finish a JOIN.

where_ :: SqlExpr (Value Bool) -> SqlQuery ()

WHERE clause: restrict the query's result.

on :: SqlExpr (Value Bool) -> SqlQuery ()

An ON clause, useful to describe how two tables are related. Cross joins and tuple-joins do not need an on clause, but InnerJoin and the various outer joins do.

Database.Esqueleto.Experimental in version 4.0.0.0 of the library. The Experimental module has a dramatically improved means for introducing tables and entities that provides more power and less potential for runtime errors.

If you don't include an on clause (or include too many!) then a runtime exception will be thrown.

As an example, consider this simple join:

select $
from $ \(foo `InnerJoin` bar) -> do
  on (foo ^. FooId ==. bar ^. BarFooId)
  ...

We need to specify the clause for joining the two columns together. If we had this:

select $
from $ \(foo `CrossJoin` bar) -> do
  ...

Then we can safely omit the on clause, because the cross join will make pairs of all records possible.

You can do multiple on clauses in a query. This query joins three tables, and has two on clauses:

select $
from $ \(foo `InnerJoin` bar `InnerJoin` baz) -> do
  on (baz ^. BazId ==. bar ^. BarBazId)
  on (foo ^. FooId ==. bar ^. BarFooId)
  ...

Old versions of esqueleto required that you provide the on clauses in reverse order. This restriction has been lifted - you can now provide on clauses in any order, and the SQL should work itself out. The above query is now totally equivalent to this:

select $
from $ \(foo `InnerJoin` bar `InnerJoin` baz) -> do
  on (foo ^. FooId ==. bar ^. BarFooId)
  on (baz ^. BazId ==. bar ^. BarBazId)
  ...

groupBy :: ToSomeValues a => a -> SqlQuery ()

GROUP BY clause. You can enclose multiple columns in a tuple.

select $ from \(foo `InnerJoin` bar) -> do
  on (foo ^. FooBarId ==. bar ^. BarId)
  groupBy (bar ^. BarId, bar ^. BarName)
  return (bar ^. BarId, bar ^. BarName, countRows)

With groupBy you can sort by aggregate functions, like so (we used let to restrict the more general countRows to SqlSqlExpr (Value Int) to avoid ambiguity---the second use of countRows has its type restricted by the :: Int below):

r <- select $ from \(foo `InnerJoin` bar) -> do
  on (foo ^. FooBarId ==. bar ^. BarId)
  groupBy $ bar ^. BarName
  let countRows' = countRows
  orderBy [asc countRows']
  return (bar ^. BarName, countRows')
forM_ r $ \(Value name, Value count) -> do
  print name
  print (count :: Int)

Need more columns?

The ToSomeValues class is defined for SqlExpr and tuples of SqlExprs. We only have definitions for up to 8 elements in a tuple right now, so it's possible that you may need to have more than 8 elements.

For example, consider a query with a groupBy call like this:

groupBy (e0, e1, e2, e3, e4, e5, e6, e7)

This is the biggest you can get with a single tuple. However, you can easily nest the tuples to add more:

groupBy ((e0, e1, e2, e3, e4, e5, e6, e7), e8, e9)

orderBy :: [SqlExpr OrderBy] -> SqlQuery ()

ORDER BY clause. See also asc and desc.

Multiple calls to orderBy get concatenated on the final query, including distinctOnOrderBy.

asc :: PersistField a => SqlExpr (Value a) -> SqlExpr OrderBy

Ascending order of this field or SqlExpression.

desc :: PersistField a => SqlExpr (Value a) -> SqlExpr OrderBy

Descending order of this field or SqlExpression.

orderByExpr :: Builder -> SqlExpr (Value a) -> SqlExpr OrderBy

limit :: Int64 -> SqlQuery ()

LIMIT. Limit the number of returned rows.

offset :: Int64 -> SqlQuery ()

OFFSET. Usually used with limit.

distinct :: SqlQuery a -> SqlQuery a

DISTINCT. Change the current SELECT into SELECT DISTINCT. For example:

select $ distinct $
  from \foo -> do
  ...

Note that this also has the same effect:

select $
  from \foo -> do
  distinct (return ())
  ...

Since: 2.2.4

distinctOn :: [SqlExpr DistinctOn] -> SqlQuery a -> SqlQuery a

DISTINCT ON. Change the current SELECT into SELECT DISTINCT ON (SqlExpressions). For example:

select $
  from \foo ->
  distinctOn [don (foo ^. FooName), don (foo ^. FooState)] $ do
  ...

You can also chain different calls to distinctOn. The above is equivalent to:

select $
  from \foo ->
  distinctOn [don (foo ^. FooName)] $
  distinctOn [don (foo ^. FooState)] $ do
  ...

Each call to distinctOn adds more SqlExpressions. Calls to distinctOn override any calls to distinct.

Note that PostgreSQL requires the SqlExpressions on DISTINCT ON to be the first ones to appear on a ORDER BY. This is not managed automatically by esqueleto, keeping its spirit of trying to be close to raw SQL.

Supported by PostgreSQL only.

Since: 2.2.4

don :: SqlExpr (Value a) -> SqlExpr DistinctOn

Erase an SqlExpression's type so that it's suitable to be used by distinctOn.

Since: 2.2.4

distinctOnOrderBy :: [SqlExpr OrderBy] -> SqlQuery a -> SqlQuery a

A convenience function that calls both distinctOn and orderBy. In other words,

distinctOnOrderBy [asc foo, desc bar, desc quux] $ do
  ...

is the same as:

distinctOn [don foo, don  bar, don  quux] $ do
  orderBy  [asc foo, desc bar, desc quux]
  ...

Since: 2.2.4

rand :: SqlExpr OrderBy

Deprecated: Since 2.6.0: rand ordering function is not uniform across all databases! To avoid accidental partiality it will be removed in the next major version.

ORDER BY random() clause.

Since: 1.3.10

having :: SqlExpr (Value Bool) -> SqlQuery ()

HAVING.

Since: 1.2.2

locking :: LockingKind -> SqlQuery ()

Add a locking clause to the query. Please read LockingKind documentation and your RDBMS manual.

If multiple calls to locking are made on the same query, the last one is used.

Since: 2.2.7

sub_select :: PersistField a => SqlQuery (SqlExpr (Value a)) -> SqlExpr (Value a)

Deprecated: sub_select sub_select is an unsafe function to use. If used with a SqlQuery that returns 0 results, then it may return NULL despite not mentioning Maybe in the return type. If it returns more than 1 result, then it will throw a SQL error. Instead, consider using one of the following alternatives: - subSelect: attaches a LIMIT 1 and the Maybe return type, totally safe. - subSelectMaybe: Attaches a LIMIT 1, useful for a query that already has a Maybe in the return type. - subSelectCount: Performs a count of the query - this is always safe. - subSelectUnsafe: Performs no checks or guarantees. Safe to use with countRows and friends.

Execute a subquery SELECT in an SqlExpression. Returns a simple value so should be used only when the SELECT query is guaranteed to return just one row.

Deprecated in 3.2.0.

subSelect :: PersistField a => SqlQuery (SqlExpr (Value a)) -> SqlExpr (Value (Maybe a))

Execute a subquery SELECT in a SqlExpr. The query passed to this function will only return a single result - it has a LIMIT 1 passed in to the query to make it safe, and the return type is Maybe to indicate that the subquery might result in 0 rows.

If you find yourself writing joinV . subSelect, then consider using subSelectMaybe.

If you're performing a countRows, then you can use subSelectCount which is safe.

If you know that the subquery will always return exactly one row (eg a foreign key constraint guarantees that you'll get exactly one row), then consider subSelectUnsafe, along with a comment explaining why it is safe.

Since: 3.2.0

subSelectMaybe :: PersistField a => SqlQuery (SqlExpr (Value (Maybe a))) -> SqlExpr (Value (Maybe a))

Execute a subquery SELECT in a SqlExpr. This function is a shorthand for the common joinV . subSelect idiom, where you are calling subSelect on an expression that would be Maybe already.

As an example, you would use this function when calling sum_ or max_, which have Maybe in the result type (for a 0 row query).

Since: 3.2.0

subSelectCount :: (Num a, PersistField a) => SqlQuery ignored -> SqlExpr (Value a)

Performs a COUNT of the given query in a subSelect manner. This is always guaranteed to return a result value, and is completely safe.

Since: 3.2.0

subSelectList :: PersistField a => SqlQuery (SqlExpr (Value a)) -> SqlExpr (ValueList a)

Execute a subquery SELECT in a SqlExpr that returns a list. This is an alias for subList_select and is provided for symmetry with the other safe subselect functions.

Since: 3.2.0

subSelectForeign

Arguments

:: (BackendCompatible SqlBackend (PersistEntityBackend val1), PersistEntity val1, PersistEntity val2, PersistField a)

=> SqlExpr (Entity val2)

An expression representing the table you have access to now.

-> EntityField val2 (Key val1)

The foreign key field on the table.

-> (SqlExpr (Entity val1) -> SqlExpr (Value a))

A function to extract a value from the foreign reference table.

-> SqlExpr (Value a)

Performs a sub-select using the given foreign key on the entity. This is useful to extract values that are known to be present by the database schema.

As an example, consider the following persistent definition:

User
  profile ProfileId

Profile
  name    Text

The following query will return the name of the user.

getUserWithName =
    select $
    from $ user ->
    pure (user, subSelectForeign user UserProfile (^. ProfileName)

Since: 3.2.0

subSelectUnsafe :: PersistField a => SqlQuery (SqlExpr (Value a)) -> SqlExpr (Value a)

Execute a subquery SELECT in a SqlExpr. This function is unsafe, because it can throw runtime exceptions in two cases:

1. If the query passed has 0 result rows, then it will return a NULL value. The persistent parsing operations will fail on an unexpected NULL.
2. If the query passed returns more than one row, then the SQL engine will fail with an error like "More than one row returned by a subquery used as an expression".

This function is safe if you guarantee that exactly one row will be returned, or if the result already has a Maybe type for some reason.

For variants with the safety encoded already, see subSelect and subSelectMaybe. For the most common safe use of this, see subSelectCount.

Since: 3.2.0

(^.) :: forall typ val. (PersistEntity val, PersistField typ) => SqlExpr (Entity val) -> EntityField val typ -> SqlExpr (Value typ) infixl 9

Project a field of an entity.

withNonNull :: PersistField typ => SqlExpr (Value (Maybe typ)) -> (SqlExpr (Value typ) -> SqlQuery a) -> SqlQuery a

Project an SqlExpression that may be null, guarding against null cases.

(?.) :: (PersistEntity val, PersistField typ) => SqlExpr (Maybe (Entity val)) -> EntityField val typ -> SqlExpr (Value (Maybe typ))

Project a field of an entity that may be null.

val :: PersistField typ => typ -> SqlExpr (Value typ)

Lift a constant value from Haskell-land to the query.

isNothing :: PersistField typ => SqlExpr (Value (Maybe typ)) -> SqlExpr (Value Bool)

IS NULL comparison.

For IS NOT NULL, you can negate this with not_, as in not_ (isNothing (person ^. PersonAge))

Warning: Persistent and Esqueleto have different behavior for != Nothing:

	Haskell	SQL
Persistent	!=. Nothing	IS NOT NULL
Esqueleto	!=. Nothing	!= NULL

In SQL, = NULL and != NULL return NULL instead of true or false. For this reason, you very likely do not want to use !=. Nothing in Esqueleto. You may find these hlint rules helpful to enforce this:

- error: {lhs: v Database.Esqueleto.==. Database.Esqueleto.nothing, rhs: Database.Esqueleto.isNothing v, name: Use Esqueleto's isNothing}
- error: {lhs: v Database.Esqueleto.==. Database.Esqueleto.val Nothing, rhs: Database.Esqueleto.isNothing v, name: Use Esqueleto's isNothing}
- error: {lhs: v Database.Esqueleto.!=. Database.Esqueleto.nothing, rhs: not_ (Database.Esqueleto.isNothing v), name: Use Esqueleto's not isNothing}
- error: {lhs: v Database.Esqueleto.!=. Database.Esqueleto.val Nothing, rhs: not_ (Database.Esqueleto.isNothing v), name: Use Esqueleto's not isNothing}

just :: SqlExpr (Value typ) -> SqlExpr (Value (Maybe typ))

Analogous to Just, promotes a value of type typ into one of type Maybe typ. It should hold that val . Just === just . val.

nothing :: SqlExpr (Value (Maybe typ))

NULL value.

joinV :: SqlExpr (Value (Maybe (Maybe typ))) -> SqlExpr (Value (Maybe typ))

Join nested Maybes in a Value into one. This is useful when calling aggregate functions on nullable fields.

countHelper :: Num a => Builder -> Builder -> SqlExpr (Value typ) -> SqlExpr (Value a)

countRows :: Num a => SqlExpr (Value a)

COUNT(*) value.

count :: Num a => SqlExpr (Value typ) -> SqlExpr (Value a)

COUNT.

countDistinct :: Num a => SqlExpr (Value typ) -> SqlExpr (Value a)

COUNT(DISTINCT x).

Since: 2.4.1

not_ :: SqlExpr (Value Bool) -> SqlExpr (Value Bool)

(==.) :: PersistField typ => SqlExpr (Value typ) -> SqlExpr (Value typ) -> SqlExpr (Value Bool) infix 4

(>=.) :: PersistField typ => SqlExpr (Value typ) -> SqlExpr (Value typ) -> SqlExpr (Value Bool) infix 4

(>.) :: PersistField typ => SqlExpr (Value typ) -> SqlExpr (Value typ) -> SqlExpr (Value Bool) infix 4

(<=.) :: PersistField typ => SqlExpr (Value typ) -> SqlExpr (Value typ) -> SqlExpr (Value Bool) infix 4

(<.) :: PersistField typ => SqlExpr (Value typ) -> SqlExpr (Value typ) -> SqlExpr (Value Bool) infix 4

(!=.) :: PersistField typ => SqlExpr (Value typ) -> SqlExpr (Value typ) -> SqlExpr (Value Bool) infix 4

(&&.) :: SqlExpr (Value Bool) -> SqlExpr (Value Bool) -> SqlExpr (Value Bool) infixr 3

(||.) :: SqlExpr (Value Bool) -> SqlExpr (Value Bool) -> SqlExpr (Value Bool) infixr 2

(+.) :: PersistField a => SqlExpr (Value a) -> SqlExpr (Value a) -> SqlExpr (Value a) infixl 6

(-.) :: PersistField a => SqlExpr (Value a) -> SqlExpr (Value a) -> SqlExpr (Value a) infixl 6

(/.) :: PersistField a => SqlExpr (Value a) -> SqlExpr (Value a) -> SqlExpr (Value a) infixl 7

(*.) :: PersistField a => SqlExpr (Value a) -> SqlExpr (Value a) -> SqlExpr (Value a) infixl 7

between :: PersistField a => SqlExpr (Value a) -> (SqlExpr (Value a), SqlExpr (Value a)) -> SqlExpr (Value Bool)

BETWEEN.

@since: 3.1.0

random_ :: (PersistField a, Num a) => SqlExpr (Value a)

Deprecated: Since 2.6.0: random_ is not uniform across all databases! Please use a specific one such as random_, random_, or random_

round_ :: (PersistField a, Num a, PersistField b, Num b) => SqlExpr (Value a) -> SqlExpr (Value b)

ceiling_ :: (PersistField a, Num a, PersistField b, Num b) => SqlExpr (Value a) -> SqlExpr (Value b)

floor_ :: (PersistField a, Num a, PersistField b, Num b) => SqlExpr (Value a) -> SqlExpr (Value b)

sum_ :: (PersistField a, PersistField b) => SqlExpr (Value a) -> SqlExpr (Value (Maybe b))

min_ :: PersistField a => SqlExpr (Value a) -> SqlExpr (Value (Maybe a))

max_ :: PersistField a => SqlExpr (Value a) -> SqlExpr (Value (Maybe a))

avg_ :: (PersistField a, PersistField b) => SqlExpr (Value a) -> SqlExpr (Value (Maybe b))

castNum :: (Num a, Num b) => SqlExpr (Value a) -> SqlExpr (Value b)

Allow a number of one type to be used as one of another type via an implicit cast. An explicit cast is not made, this function changes only the types on the Haskell side.

Caveat: Trying to use castNum from Double to Int will not result in an integer, the original fractional number will still be used! Use round_, ceiling_ or floor_ instead.

Safety: This operation is mostly safe due to the Num constraint between the types and the fact that RDBMSs usually allow numbers of different types to be used interchangeably. However, there may still be issues with the query not being accepted by the RDBMS or persistent not being able to parse it.

Since: 2.2.9

castNumM :: (Num a, Num b) => SqlExpr (Value (Maybe a)) -> SqlExpr (Value (Maybe b))

Same as castNum, but for nullable values.

Since: 2.2.9

coalesce :: PersistField a => [SqlExpr (Value (Maybe a))] -> SqlExpr (Value (Maybe a))

COALESCE function. Evaluates the arguments in order and returns the value of the first non-NULL SqlExpression, or NULL (Nothing) otherwise. Some RDBMSs (such as SQLite) require at least two arguments; please refer to the appropriate documentation.

Since: 1.4.3

coalesceDefault :: PersistField a => [SqlExpr (Value (Maybe a))] -> SqlExpr (Value a) -> SqlExpr (Value a)

Like coalesce, but takes a non-nullable SqlExpression placed at the end of the SqlExpression list, which guarantees a non-NULL result.

Since: 1.4.3

lower_ :: SqlString s => SqlExpr (Value s) -> SqlExpr (Value s)

LOWER function.

upper_ :: SqlString s => SqlExpr (Value s) -> SqlExpr (Value s)

UPPER function. @since 3.3.0

trim_ :: SqlString s => SqlExpr (Value s) -> SqlExpr (Value s)

TRIM function. @since 3.3.0

rtrim_ :: SqlString s => SqlExpr (Value s) -> SqlExpr (Value s)

RTRIM function. @since 3.3.0

ltrim_ :: SqlString s => SqlExpr (Value s) -> SqlExpr (Value s)

LTRIM function. @since 3.3.0

length_ :: (SqlString s, Num a) => SqlExpr (Value s) -> SqlExpr (Value a)

LENGTH function. @since 3.3.0

left_ :: (SqlString s, Num a) => (SqlExpr (Value s), SqlExpr (Value a)) -> SqlExpr (Value s)

LEFT function. @since 3.3.0

right_ :: (SqlString s, Num a) => (SqlExpr (Value s), SqlExpr (Value a)) -> SqlExpr (Value s)

RIGHT function. @since 3.3.0

like :: SqlString s => SqlExpr (Value s) -> SqlExpr (Value s) -> SqlExpr (Value Bool) infixr 2

LIKE operator.

ilike :: SqlString s => SqlExpr (Value s) -> SqlExpr (Value s) -> SqlExpr (Value Bool) infixr 2

ILIKE operator (case-insensitive LIKE).

Supported by PostgreSQL only.

Since: 2.2.3

(%) :: SqlString s => SqlExpr (Value s)

The string %. May be useful while using like and concatenation (concat_ or ++., depending on your database). Note that you always have to type the parenthesis, for example:

name `like` (%) ++. val "John" ++. (%)

concat_ :: SqlString s => [SqlExpr (Value s)] -> SqlExpr (Value s)

The CONCAT function with a variable number of parameters. Supported by MySQL and PostgreSQL.

(++.) :: SqlString s => SqlExpr (Value s) -> SqlExpr (Value s) -> SqlExpr (Value s) infixr 5

The || string concatenation operator (named after Haskell's ++ in order to avoid naming clash with ||.). Supported by SQLite and PostgreSQL.

castString :: (SqlString s, SqlString r) => SqlExpr (Value s) -> SqlExpr (Value r)

Cast a string type into Text. This function is very useful if you want to use newtypes, or if you want to apply functions such as like to strings of different types.

Safety: This is a slightly unsafe function, especially if you have defined your own instances of SqlString. Also, since Maybe is an instance of SqlString, it's possible to turn a nullable value into a non-nullable one. Avoid using this function if possible.

subList_select :: PersistField a => SqlQuery (SqlExpr (Value a)) -> SqlExpr (ValueList a)

Execute a subquery SELECT in an SqlExpression. Returns a list of values.

valList :: PersistField typ => [typ] -> SqlExpr (ValueList typ)

Lift a list of constant value from Haskell-land to the query.

justList :: SqlExpr (ValueList typ) -> SqlExpr (ValueList (Maybe typ))

Same as just but for ValueList. Most of the time you won't need it, though, because you can use just from inside subList_select or Just from inside valList.

Since: 2.2.12

in_ :: PersistField typ => SqlExpr (Value typ) -> SqlExpr (ValueList typ) -> SqlExpr (Value Bool)

IN operator. For example if you want to select all Persons by a list of IDs:

SELECT *
FROM Person
WHERE Person.id IN (?)

In esqueleto, we may write the same query above as:

select $
from $ \person -> do
where_ $ person ^. PersonId `in_` valList personIds
return person

Where personIds is of type [Key Person].

notIn :: PersistField typ => SqlExpr (Value typ) -> SqlExpr (ValueList typ) -> SqlExpr (Value Bool)

NOT IN operator.

exists :: SqlQuery () -> SqlExpr (Value Bool)

EXISTS operator. For example:

select $
from $ \person -> do
where_ $ exists $
         from $ \post -> do
         where_ (post ^. BlogPostAuthorId ==. person ^. PersonId)
return person

notExists :: SqlQuery () -> SqlExpr (Value Bool)

NOT EXISTS operator.

set :: PersistEntity val => SqlExpr (Entity val) -> [SqlExpr (Entity val) -> SqlExpr Update] -> SqlQuery ()

SET clause used on UPDATEs. Note that while it's not a type error to use this function on a SELECT, it will most certainly result in a runtime error.

(=.) :: (PersistEntity val, PersistField typ) => EntityField val typ -> SqlExpr (Value typ) -> SqlExpr (Entity val) -> SqlExpr Update infixr 3

(+=.) :: (PersistEntity val, PersistField a) => EntityField val a -> SqlExpr (Value a) -> SqlExpr (Entity val) -> SqlExpr Update infixr 3

(-=.) :: (PersistEntity val, PersistField a) => EntityField val a -> SqlExpr (Value a) -> SqlExpr (Entity val) -> SqlExpr Update infixr 3

(*=.) :: (PersistEntity val, PersistField a) => EntityField val a -> SqlExpr (Value a) -> SqlExpr (Entity val) -> SqlExpr Update infixr 3

(/=.) :: (PersistEntity val, PersistField a) => EntityField val a -> SqlExpr (Value a) -> SqlExpr (Entity val) -> SqlExpr Update infixr 3

(<#) :: (a -> b) -> SqlExpr (Value a) -> SqlExpr (Insertion b)

Apply a PersistField constructor to SqlExpr Value arguments.

(<&>) :: SqlExpr (Insertion (a -> b)) -> SqlExpr (Value a) -> SqlExpr (Insertion b)

Apply extra SqlExpr Value arguments to a PersistField constructor

case_ :: PersistField a => [(SqlExpr (Value Bool), SqlExpr (Value a))] -> SqlExpr (Value a) -> SqlExpr (Value a)

CASE statement. For example:

select $
return $
case_
   [ when_
       (exists $
       from $ \p -> do
       where_ (p ^. PersonName ==. val "Mike"))
     then_
       (sub_select $
       from $ \v -> do
       let sub =
               from $ \c -> do
               where_ (c ^. PersonName ==. val "Mike")
               return (c ^. PersonFavNum)
       where_ (v ^. PersonFavNum >. sub_select sub)
       return $ count (v ^. PersonName) +. val (1 :: Int)) ]
   (else_ $ val (-1))

This query is a bit complicated, but basically it checks if a person named "Mike" exists, and if that person does, run the subquery to find out how many people have a ranking (by Fav Num) higher than "Mike".

NOTE: There are a few things to be aware about this statement.

• This only implements the full CASE statement, it does not implement the "simple" CASE statement.
• At least one when_ and then_ is mandatory otherwise it will emit an error.
• The else_ is also mandatory, unlike the SQL statement in which if the ELSE is omitted it will return a NULL. You can reproduce this via nothing.

Since: 2.1.2

toBaseId :: ToBaseId ent => SqlExpr (Value (Key ent)) -> SqlExpr (Value (Key (BaseEnt ent)))

Convert an entity's key into another entity's.

This function is to be used when you change an entity's Id to be that of another entity. For example:

Bar
  barNum Int
Foo
  bar BarId
  fooNum Int
  Primary bar

In this example, Bar is said to be the BaseEnt(ity), and Foo the child. To model this in Esqueleto, declare:

instance ToBaseId Foo where
  type BaseEnt Foo = Bar
  toBaseIdWitness barId = FooKey barId

Now you're able to write queries such as:

select $
from $ (bar `InnerJoin` foo) -> do
on (toBaseId (foo ^. FooId) ==. bar ^. BarId)
return (bar, foo)

Note: this function may be unsafe to use in conditions not like the one of the example above.

Since: 2.4.3

when_ :: expr (Value Bool) -> () -> expr a -> (expr (Value Bool), expr a)

Syntax sugar for case_.

Since: 2.1.2

then_ :: ()

Syntax sugar for case_.

Since: 2.1.2

else_ :: expr a -> expr a

Syntax sugar for case_.

Since: 2.1.2

newtype Value a

A single value (as opposed to a whole entity). You may use (^.) or (?.) to get a Value from an Entity.

Constructors

Value

Fields

• unValue :: a

Instances

Applicative Value

Defined in Database.Esqueleto.Internal.Internal

Methods

pure :: a -> Value a

(<*>) :: Value (a -> b) -> Value a -> Value b

liftA2 :: (a -> b -> c) -> Value a -> Value b -> Value c

(*>) :: Value a -> Value b -> Value b

(<*) :: Value a -> Value b -> Value a

Functor Value

Since: 1.4.4

Defined in Database.Esqueleto.Internal.Internal

Methods

fmap :: (a -> b) -> Value a -> Value b

(<$) :: a -> Value b -> Value a

Monad Value

Defined in Database.Esqueleto.Internal.Internal

Methods

(>>=) :: Value a -> (a -> Value b) -> Value b

(>>) :: Value a -> Value b -> Value b

return :: a -> Value a

(PersistEntity rec, PersistField typ, SymbolToField sym rec typ) => HasField (sym :: Symbol) (SqlExpr (Entity rec)) (SqlExpr (Value typ))

This instance allows you to use record.field notation with GHC 9.2's OverloadedRecordDot extension.

Example:

-- persistent model:
BlogPost
    authorId     PersonId
    title        Text

-- query:
select $ do
    bp <- from $ table @BlogPost
    pure $ bp.title

This is exactly equivalent to the following:

blogPost :: SqlExpr (Entity BlogPost)

blogPost ^. BlogPostTitle
blogPost ^. #title
blogPost.title

There's another instance defined on SqlExpr (Entity (Maybe rec)), which allows you to project from a LEFT JOINed entity.

Since: 3.5.4.0

Defined in Database.Esqueleto.Internal.Internal

Methods

getField :: SqlExpr (Entity rec) -> SqlExpr (Value typ)

(PersistEntity rec, PersistField typ, SymbolToField sym rec typ) => HasField (sym :: Symbol) (SqlExpr (Maybe (Entity rec))) (SqlExpr (Value (Maybe typ)))

This instance allows you to use record.field notation with GC 9.2's OverloadedRecordDot extension.

Example:

-- persistent model:
Person
    name         Text

BlogPost
    title        Text
    authorId     PersonId

-- query:

select $ do
    (p :& bp) <- from $
        table Person
        leftJoin table BlogPost
        on do
            \(p :& bp) ->
                just p.id ==. bp.authorId
    pure (p.name, bp.title)

The following forms are all equivalent:

blogPost :: SqlExpr (Maybe (Entity BlogPost))

blogPost ?. BlogPostTitle
blogPost ?. #title
blogPost.title

Since: 3.5.4.0

Defined in Database.Esqueleto.Internal.Internal

Methods

getField :: SqlExpr (Maybe (Entity rec)) -> SqlExpr (Value (Maybe typ))

(ToFrom a a', SqlSelect b r, ToAlias b, ToAliasReference b, d ~ (a' :& b)) => DoInnerJoin Lateral a (a' -> SqlQuery b, d -> SqlExpr (Value Bool)) d

Defined in Database.Esqueleto.Experimental.From.Join

Methods

doInnerJoin :: Proxy Lateral -> a -> (a' -> SqlQuery b, d -> SqlExpr (Value Bool)) -> From d

(ToFrom a a', ToMaybe b, d ~ (a' :& ToMaybeT b), SqlSelect b r, ToAlias b, ToAliasReference b) => DoLeftJoin Lateral a (a' -> SqlQuery b, d -> SqlExpr (Value Bool)) d

Defined in Database.Esqueleto.Experimental.From.Join

Methods

doLeftJoin :: Proxy Lateral -> a -> (a' -> SqlQuery b, d -> SqlExpr (Value Bool)) -> From d

Show a => Show (Value a)

Defined in Database.Esqueleto.Internal.Internal

Methods

showsPrec :: Int -> Value a -> ShowS

show :: Value a -> String

showList :: [Value a] -> ShowS

ToAlias (SqlExpr (Value a))

Defined in Database.Esqueleto.Experimental.ToAlias

Methods

toAlias :: SqlExpr (Value a) -> SqlQuery (SqlExpr (Value a))

ToAliasReference (SqlExpr (Value a))

Defined in Database.Esqueleto.Experimental.ToAliasReference

Methods

toAliasReference :: Ident -> SqlExpr (Value a) -> SqlQuery (SqlExpr (Value a))

ToMaybe (SqlExpr (Value a))

Defined in Database.Esqueleto.Experimental.ToMaybe

Associated Types

type ToMaybeT (SqlExpr (Value a))

Methods

toMaybe :: SqlExpr (Value a) -> ToMaybeT (SqlExpr (Value a))

ToSomeValues (SqlExpr (Value a))

Defined in Database.Esqueleto.Internal.Internal

Methods

toSomeValues :: SqlExpr (Value a) -> [SomeValue]

Eq a => Eq (Value a)

Defined in Database.Esqueleto.Internal.Internal

Methods

(==) :: Value a -> Value a -> Bool

(/=) :: Value a -> Value a -> Bool

Ord a => Ord (Value a)

Defined in Database.Esqueleto.Internal.Internal

Methods

compare :: Value a -> Value a -> Ordering

(<) :: Value a -> Value a -> Bool

(<=) :: Value a -> Value a -> Bool

(>) :: Value a -> Value a -> Bool

(>=) :: Value a -> Value a -> Bool

max :: Value a -> Value a -> Value a

min :: Value a -> Value a -> Value a

PersistField a => SqlSelect (SqlExpr (Value a)) (Value a)

You may return any single value (i.e. a single column) from a select query.

Defined in Database.Esqueleto.Internal.Internal

Methods

sqlSelectCols :: IdentInfo -> SqlExpr (Value a) -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy (SqlExpr (Value a)) -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text (Value a)

sqlInsertInto :: IdentInfo -> SqlExpr (Value a) -> (Builder, [PersistValue])

type ToMaybeT (SqlExpr (Value a))

Defined in Database.Esqueleto.Experimental.ToMaybe

type ToMaybeT (SqlExpr (Value a)) = SqlExpr (Value (Maybe (Nullable a)))

newtype ValueList a

A list of single values. There's a limited set of functions able to work with this data type (such as subList_select, valList, in_ and exists).

Constructors

ValueList a

Instances

Show a => Show (ValueList a)

Defined in Database.Esqueleto.Internal.Internal

Methods

showsPrec :: Int -> ValueList a -> ShowS

show :: ValueList a -> String

showList :: [ValueList a] -> ShowS

Eq a => Eq (ValueList a)

Defined in Database.Esqueleto.Internal.Internal

Methods

(==) :: ValueList a -> ValueList a -> Bool

(/=) :: ValueList a -> ValueList a -> Bool

Ord a => Ord (ValueList a)

Defined in Database.Esqueleto.Internal.Internal

Methods

compare :: ValueList a -> ValueList a -> Ordering

(<) :: ValueList a -> ValueList a -> Bool

(<=) :: ValueList a -> ValueList a -> Bool

(>) :: ValueList a -> ValueList a -> Bool

(>=) :: ValueList a -> ValueList a -> Bool

max :: ValueList a -> ValueList a -> ValueList a

min :: ValueList a -> ValueList a -> ValueList a

data SomeValue where

A wrapper type for for any expr (Value a) for all a.

Constructors

SomeValue :: SqlExpr (Value a) -> SomeValue

class ToSomeValues a where

A class of things that can be converted into a list of SomeValue. It has instances for tuples and is the reason why groupBy can take tuples, like groupBy (foo ^. FooId, foo ^. FooName, foo ^. FooType).

Methods

toSomeValues :: a -> [SomeValue]

Instances

ToSomeValues (SqlExpr (Value a))

Defined in Database.Esqueleto.Internal.Internal

Methods

toSomeValues :: SqlExpr (Value a) -> [SomeValue]

(ToSomeValues a, ToSomeValues b) => ToSomeValues (a, b)

Defined in Database.Esqueleto.Internal.Internal

Methods

toSomeValues :: (a, b) -> [SomeValue]

(ToSomeValues a, ToSomeValues b, ToSomeValues c) => ToSomeValues (a, b, c)

Defined in Database.Esqueleto.Internal.Internal

Methods

toSomeValues :: (a, b, c) -> [SomeValue]

(ToSomeValues a, ToSomeValues b, ToSomeValues c, ToSomeValues d) => ToSomeValues (a, b, c, d)

Defined in Database.Esqueleto.Internal.Internal

Methods

toSomeValues :: (a, b, c, d) -> [SomeValue]

(ToSomeValues a, ToSomeValues b, ToSomeValues c, ToSomeValues d, ToSomeValues e) => ToSomeValues (a, b, c, d, e)

Defined in Database.Esqueleto.Internal.Internal

Methods

toSomeValues :: (a, b, c, d, e) -> [SomeValue]

(ToSomeValues a, ToSomeValues b, ToSomeValues c, ToSomeValues d, ToSomeValues e, ToSomeValues f) => ToSomeValues (a, b, c, d, e, f)

Defined in Database.Esqueleto.Internal.Internal

Methods

toSomeValues :: (a, b, c, d, e, f) -> [SomeValue]

(ToSomeValues a, ToSomeValues b, ToSomeValues c, ToSomeValues d, ToSomeValues e, ToSomeValues f, ToSomeValues g) => ToSomeValues (a, b, c, d, e, f, g)

Defined in Database.Esqueleto.Internal.Internal

Methods

toSomeValues :: (a, b, c, d, e, f, g) -> [SomeValue]

(ToSomeValues a, ToSomeValues b, ToSomeValues c, ToSomeValues d, ToSomeValues e, ToSomeValues f, ToSomeValues g, ToSomeValues h) => ToSomeValues (a, b, c, d, e, f, g, h)

Defined in Database.Esqueleto.Internal.Internal

Methods

toSomeValues :: (a, b, c, d, e, f, g, h) -> [SomeValue]

type family KnowResult a where ...

Equations

KnowResult (i -> o) = KnowResult o

KnowResult a = a

class FinalResult a where

A class for constructors or function which result type is known.

Since: 3.1.3

Methods

finalR :: a -> KnowResult a

Instances

FinalResult (Unique val)

Defined in Database.Esqueleto.Internal.Internal

Methods

finalR :: Unique val -> KnowResult (Unique val)

FinalResult b => FinalResult (a -> b)

Defined in Database.Esqueleto.Internal.Internal

Methods

finalR :: (a -> b) -> KnowResult (a -> b)

toUniqueDef :: forall a val. (KnowResult a ~ Unique val, PersistEntity val, FinalResult a) => a -> UniqueDef

Convert a constructor for a Unique key on a record to the UniqueDef that defines it. You can supply just the constructor itself, or a value of the type - the library is capable of figuring it out from there.

Since: 3.1.3

renderUpdates :: BackendCompatible SqlBackend backend => backend -> [SqlExpr (Entity val) -> SqlExpr Update] -> (Builder, [PersistValue])

Render updates to be use in a SET clause for a given sql backend.

Since: 3.1.3

data InnerJoin a b infixl 2

Data type that represents an INNER JOIN (see LeftOuterJoin for an example).

Constructors

a `InnerJoin` b infixl 2

Instances

IsJoinKind InnerJoin

Defined in Database.Esqueleto.Internal.Internal

Methods

smartJoin :: a -> b -> InnerJoin a b

reifyJoinKind :: InnerJoin a b -> JoinKind

FromPreprocess (InnerJoin a b) => From (InnerJoin a b)

Defined in Database.Esqueleto.Internal.Internal

Methods

from_ :: SqlQuery (InnerJoin a b)

(DoInnerJoin lateral lhs rhs r, lateral ~ IsLateral rhs) => ToFrom (InnerJoin lhs rhs) r

Defined in Database.Esqueleto.Experimental.From.Join

Methods

toFrom :: InnerJoin lhs rhs -> From r

data CrossJoin a b infixl 2

Data type that represents a CROSS JOIN (see LeftOuterJoin for an example).

Constructors

a `CrossJoin` b infixl 2

Instances

IsJoinKind CrossJoin

Defined in Database.Esqueleto.Internal.Internal

Methods

smartJoin :: a -> b -> CrossJoin a b

reifyJoinKind :: CrossJoin a b -> JoinKind

FromPreprocess (CrossJoin a b) => From (CrossJoin a b)

Defined in Database.Esqueleto.Internal.Internal

Methods

from_ :: SqlQuery (CrossJoin a b)

(DoCrossJoin lateral lhs rhs r, IsLateral rhs ~ lateral) => ToFrom (CrossJoin lhs rhs) r

Defined in Database.Esqueleto.Experimental.From.Join

Methods

toFrom :: CrossJoin lhs rhs -> From r

data LeftOuterJoin a b infixl 2

Data type that represents a LEFT OUTER JOIN. For example,

select $
from $ \(person `LeftOuterJoin` pet) ->
  ...

is translated into

SELECT ...
FROM Person LEFT OUTER JOIN Pet
...

See also: from.

Constructors

a `LeftOuterJoin` b infixl 2

Instances

IsJoinKind LeftOuterJoin

Defined in Database.Esqueleto.Internal.Internal

Methods

smartJoin :: a -> b -> LeftOuterJoin a b

reifyJoinKind :: LeftOuterJoin a b -> JoinKind

FromPreprocess (LeftOuterJoin a b) => From (LeftOuterJoin a b)

Defined in Database.Esqueleto.Internal.Internal

Methods

from_ :: SqlQuery (LeftOuterJoin a b)

(DoLeftJoin lateral lhs rhs r, lateral ~ IsLateral rhs) => ToFrom (LeftOuterJoin lhs rhs) r

Defined in Database.Esqueleto.Experimental.From.Join

Methods

toFrom :: LeftOuterJoin lhs rhs -> From r

data RightOuterJoin a b infixl 2

Data type that represents a RIGHT OUTER JOIN (see LeftOuterJoin for an example).

Constructors

a `RightOuterJoin` b infixl 2

Instances

IsJoinKind RightOuterJoin

Defined in Database.Esqueleto.Internal.Internal

Methods

smartJoin :: a -> b -> RightOuterJoin a b

reifyJoinKind :: RightOuterJoin a b -> JoinKind

FromPreprocess (RightOuterJoin a b) => From (RightOuterJoin a b)

Defined in Database.Esqueleto.Internal.Internal

Methods

from_ :: SqlQuery (RightOuterJoin a b)

(ToFrom a a', ToFrom b b', ToMaybe a', ToMaybeT a' ~ ma, HasOnClause rhs (ma :& b'), ErrorOnLateral b, rhs ~ (b, (ma :& b') -> SqlExpr (Value Bool))) => ToFrom (RightOuterJoin a rhs) (ma :& b')

Defined in Database.Esqueleto.Experimental.From.Join

Methods

toFrom :: RightOuterJoin a rhs -> From (ma :& b')

data FullOuterJoin a b infixl 2

Data type that represents a FULL OUTER JOIN (see LeftOuterJoin for an example).

Constructors

a `FullOuterJoin` b infixl 2

Instances

IsJoinKind FullOuterJoin

Defined in Database.Esqueleto.Internal.Internal

Methods

smartJoin :: a -> b -> FullOuterJoin a b

reifyJoinKind :: FullOuterJoin a b -> JoinKind

FromPreprocess (FullOuterJoin a b) => From (FullOuterJoin a b)

Defined in Database.Esqueleto.Internal.Internal

Methods

from_ :: SqlQuery (FullOuterJoin a b)

(ToFrom a a', ToFrom b b', ToMaybe a', ToMaybeT a' ~ ma, ToMaybe b', ToMaybeT b' ~ mb, HasOnClause rhs (ma :& mb), ErrorOnLateral b, rhs ~ (b, (ma :& mb) -> SqlExpr (Value Bool))) => ToFrom (FullOuterJoin a rhs) (ma :& mb)

Defined in Database.Esqueleto.Experimental.From.Join

Methods

toFrom :: FullOuterJoin a rhs -> From (ma :& mb)

data JoinKind

(Internal) A kind of JOIN.

Constructors

InnerJoinKind

INNER JOIN

CrossJoinKind

CROSS JOIN

LeftOuterJoinKind

LEFT OUTER JOIN

RightOuterJoinKind

RIGHT OUTER JOIN

FullOuterJoinKind

FULL OUTER JOIN

Instances

Show JoinKind

Defined in Database.Esqueleto.Internal.Internal

Methods

showsPrec :: Int -> JoinKind -> ShowS

show :: JoinKind -> String

showList :: [JoinKind] -> ShowS

Eq JoinKind

Defined in Database.Esqueleto.Internal.Internal

Methods

(==) :: JoinKind -> JoinKind -> Bool

(/=) :: JoinKind -> JoinKind -> Bool

class IsJoinKind join where

(Internal) Functions that operate on types (that should be) of kind JoinKind.

Methods

smartJoin :: a -> b -> join a b

(Internal) smartJoin a b is a JOIN of the correct kind.

reifyJoinKind :: join a b -> JoinKind

(Internal) Reify a JoinKind from a JOIN. This function is non-strict.

Instances

IsJoinKind CrossJoin

Defined in Database.Esqueleto.Internal.Internal

Methods

smartJoin :: a -> b -> CrossJoin a b

reifyJoinKind :: CrossJoin a b -> JoinKind

IsJoinKind FullOuterJoin

Defined in Database.Esqueleto.Internal.Internal

Methods

smartJoin :: a -> b -> FullOuterJoin a b

reifyJoinKind :: FullOuterJoin a b -> JoinKind

IsJoinKind InnerJoin

Defined in Database.Esqueleto.Internal.Internal

Methods

smartJoin :: a -> b -> InnerJoin a b

reifyJoinKind :: InnerJoin a b -> JoinKind

IsJoinKind LeftOuterJoin

Defined in Database.Esqueleto.Internal.Internal

Methods

smartJoin :: a -> b -> LeftOuterJoin a b

reifyJoinKind :: LeftOuterJoin a b -> JoinKind

IsJoinKind RightOuterJoin

Defined in Database.Esqueleto.Internal.Internal

Methods

smartJoin :: a -> b -> RightOuterJoin a b

reifyJoinKind :: RightOuterJoin a b -> JoinKind

data OnClauseWithoutMatchingJoinException

Exception thrown whenever on is used to create an ON clause but no matching JOIN is found.

Constructors

OnClauseWithoutMatchingJoinException String

Instances

Exception OnClauseWithoutMatchingJoinException

Defined in Database.Esqueleto.Internal.Internal

Methods

toException :: OnClauseWithoutMatchingJoinException -> SomeException

fromException :: SomeException -> Maybe OnClauseWithoutMatchingJoinException

displayException :: OnClauseWithoutMatchingJoinException -> String

Show OnClauseWithoutMatchingJoinException

Defined in Database.Esqueleto.Internal.Internal

Methods

showsPrec :: Int -> OnClauseWithoutMatchingJoinException -> ShowS

show :: OnClauseWithoutMatchingJoinException -> String

showList :: [OnClauseWithoutMatchingJoinException] -> ShowS

Eq OnClauseWithoutMatchingJoinException

Defined in Database.Esqueleto.Internal.Internal

Methods

(==) :: OnClauseWithoutMatchingJoinException -> OnClauseWithoutMatchingJoinException -> Bool

(/=) :: OnClauseWithoutMatchingJoinException -> OnClauseWithoutMatchingJoinException -> Bool

Ord OnClauseWithoutMatchingJoinException

Defined in Database.Esqueleto.Internal.Internal

Methods

compare :: OnClauseWithoutMatchingJoinException -> OnClauseWithoutMatchingJoinException -> Ordering

(<) :: OnClauseWithoutMatchingJoinException -> OnClauseWithoutMatchingJoinException -> Bool

(<=) :: OnClauseWithoutMatchingJoinException -> OnClauseWithoutMatchingJoinException -> Bool

(>) :: OnClauseWithoutMatchingJoinException -> OnClauseWithoutMatchingJoinException -> Bool

(>=) :: OnClauseWithoutMatchingJoinException -> OnClauseWithoutMatchingJoinException -> Bool

max :: OnClauseWithoutMatchingJoinException -> OnClauseWithoutMatchingJoinException -> OnClauseWithoutMatchingJoinException

min :: OnClauseWithoutMatchingJoinException -> OnClauseWithoutMatchingJoinException -> OnClauseWithoutMatchingJoinException

data OrderBy

Phantom type used by orderBy, asc and desc.

data DistinctOn

Phantom type used by distinctOn and don.

data Update

Phantom type for a SET operation on an entity of the given type (see set and (=.)).

data Insertion a

Phantom type used by insertSelect.

Instances

PersistEntity e => SqlSelect (SqlExpr (Insertion e)) (Insertion e)

INSERT INTO hack.

Defined in Database.Esqueleto.Internal.Internal

Methods

sqlSelectCols :: IdentInfo -> SqlExpr (Insertion e) -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy (SqlExpr (Insertion e)) -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text (Insertion e)

sqlInsertInto :: IdentInfo -> SqlExpr (Insertion e) -> (Builder, [PersistValue])

data LockingKind

Different kinds of locking clauses supported by locking.

Note that each RDBMS has different locking support. The constructors of this datatype specify only the syntax of the locking mechanism, not its semantics. For example, even though both MySQL and PostgreSQL support ForUpdate, there are no guarantees that they will behave the same.

Since: 2.2.7

Constructors

ForUpdate

FOR UPDATE syntax. Supported by MySQL, Oracle and PostgreSQL.

Since: 2.2.7

ForUpdateSkipLocked

FOR UPDATE SKIP LOCKED syntax. Supported by MySQL, Oracle and PostgreSQL.

Since: 2.2.7

ForShare

FOR SHARE syntax. Supported by PostgreSQL.

Since: 2.2.7

LockInShareMode

LOCK IN SHARE MODE syntax. Supported by MySQL.

Since: 2.2.7

class PersistField a => SqlString a

Phantom class of data types that are treated as strings by the RDBMS. It has no methods because it's only used to avoid type errors such as trying to concatenate integers.

If you have a custom data type or newtype, feel free to make it an instance of this class.

Since: 2.4.0

Instances

SqlString Html

Since: 2.3.0

Defined in Database.Esqueleto.Internal.Internal

SqlString ByteString

Since: 2.3.0

Defined in Database.Esqueleto.Internal.Internal

SqlString Text

Since: 2.3.0

Defined in Database.Esqueleto.Internal.Internal

SqlString Text

Since: 2.3.0

Defined in Database.Esqueleto.Internal.Internal

SqlString a => SqlString (Maybe a)

Since: 2.4.0

Defined in Database.Esqueleto.Internal.Internal

a ~ Char => SqlString [a]

Since: 2.3.0

Defined in Database.Esqueleto.Internal.Internal

class ToBaseId ent where

Class that enables one to use toBaseId to convert an entity's key on a query into another (cf. toBaseId).

Associated Types

type BaseEnt ent :: Type

e.g. type BaseEnt MyBase = MyChild

Methods

toBaseIdWitness :: Key (BaseEnt ent) -> Key ent

Convert from the key of the BaseEnt(ity) to the key of the child entity. This function is not actually called, but that it typechecks proves this operation is safe.

from :: From a => (a -> SqlQuery b) -> SqlQuery b

FROM clause: bring entities into scope.

Note that this function will be replaced by the one in Database.Esqueleto.Experimental in version 4.0.0.0 of the library. The Experimental module has a dramatically improved means for introducing tables and entities that provides more power and less potential for runtime errors.

This function internally uses two type classes in order to provide some flexibility of how you may call it. Internally we refer to these type classes as the two different magics.

The innermost magic allows you to use from with the following types:

• expr (Entity val), which brings a single entity into scope.
• expr (Maybe (Entity val)), which brings a single entity that may be NULL into scope. Used for OUTER JOINs.
• A JOIN of any other two types allowed by the innermost magic, where a JOIN may be an InnerJoin, a CrossJoin, a LeftOuterJoin, a RightOuterJoin, or a FullOuterJoin. The JOINs have left fixity.

The outermost magic allows you to use from on any tuples of types supported by innermost magic (and also tuples of tuples, and so on), up to 8-tuples.

Note that using from for the same entity twice does work and corresponds to a self-join. You don't even need to use two different calls to from, you may use a JOIN or a tuple.

The following are valid examples of uses of from (the types of the arguments of the lambda are inside square brackets):

from $ \person -> ...
from $ \(person, blogPost) -> ...
from $ \(p `LeftOuterJoin` mb) -> ...
from $ \(p1 `InnerJoin` f `InnerJoin` p2) -> ...
from $ \((p1 `InnerJoin` f) `InnerJoin` p2) -> ...

The types of the arguments to the lambdas above are, respectively:

person
  :: ( Esqueleto query expr backend
     , PersistEntity Person
     , PersistEntityBackend Person ~ backend
     ) => expr (Entity Person)
(person, blogPost)
  :: (...) => (expr (Entity Person), expr (Entity BlogPost))
(p `LeftOuterJoin` mb)
  :: (...) => InnerJoin (expr (Entity Person)) (expr (Maybe (Entity BlogPost)))
(p1 `InnerJoin` f `InnerJoin` p2)
  :: (...) => InnerJoin
                (InnerJoin (expr (Entity Person))
                           (expr (Entity Follow)))
                (expr (Entity Person))
(p1 `InnerJoin` (f `InnerJoin` p2)) ::
  :: (...) => InnerJoin
                (expr (Entity Person))
                (InnerJoin (expr (Entity Follow))
                           (expr (Entity Person)))

Note that some backends may not support all kinds of JOINs.

class From a where

(Internal) Class that implements the tuple from magic (see fromStart).

Methods

from_ :: SqlQuery a

Instances

FromPreprocess (SqlExpr (Entity val)) => From (SqlExpr (Entity val))

Defined in Database.Esqueleto.Internal.Internal

Methods

from_ :: SqlQuery (SqlExpr (Entity val))

FromPreprocess (SqlExpr (Maybe (Entity val))) => From (SqlExpr (Maybe (Entity val)))

Defined in Database.Esqueleto.Internal.Internal

Methods

from_ :: SqlQuery (SqlExpr (Maybe (Entity val)))

FromPreprocess (CrossJoin a b) => From (CrossJoin a b)

Defined in Database.Esqueleto.Internal.Internal

Methods

from_ :: SqlQuery (CrossJoin a b)

FromPreprocess (FullOuterJoin a b) => From (FullOuterJoin a b)

Defined in Database.Esqueleto.Internal.Internal

Methods

from_ :: SqlQuery (FullOuterJoin a b)

FromPreprocess (InnerJoin a b) => From (InnerJoin a b)

Defined in Database.Esqueleto.Internal.Internal

Methods

from_ :: SqlQuery (InnerJoin a b)

FromPreprocess (LeftOuterJoin a b) => From (LeftOuterJoin a b)

Defined in Database.Esqueleto.Internal.Internal

Methods

from_ :: SqlQuery (LeftOuterJoin a b)

FromPreprocess (RightOuterJoin a b) => From (RightOuterJoin a b)

Defined in Database.Esqueleto.Internal.Internal

Methods

from_ :: SqlQuery (RightOuterJoin a b)

(From a, From b) => From (a, b)

Defined in Database.Esqueleto.Internal.Internal

Methods

from_ :: SqlQuery (a, b)

(From a, From b, From c) => From (a, b, c)

Defined in Database.Esqueleto.Internal.Internal

Methods

from_ :: SqlQuery (a, b, c)

(From a, From b, From c, From d) => From (a, b, c, d)

Defined in Database.Esqueleto.Internal.Internal

Methods

from_ :: SqlQuery (a, b, c, d)

(From a, From b, From c, From d, From e) => From (a, b, c, d, e)

Defined in Database.Esqueleto.Internal.Internal

Methods

from_ :: SqlQuery (a, b, c, d, e)

(From a, From b, From c, From d, From e, From f) => From (a, b, c, d, e, f)

Defined in Database.Esqueleto.Internal.Internal

Methods

from_ :: SqlQuery (a, b, c, d, e, f)

(From a, From b, From c, From d, From e, From f, From g) => From (a, b, c, d, e, f, g)

Defined in Database.Esqueleto.Internal.Internal

Methods

from_ :: SqlQuery (a, b, c, d, e, f, g)

(From a, From b, From c, From d, From e, From f, From g, From h) => From (a, b, c, d, e, f, g, h)

Defined in Database.Esqueleto.Internal.Internal

Methods

from_ :: SqlQuery (a, b, c, d, e, f, g, h)

class FromPreprocess a where

(Internal) Class that implements the JOIN from magic (see fromStart).

Methods

fromPreprocess :: SqlQuery (PreprocessedFrom a)

Instances

(PersistEntity val, BackendCompatible SqlBackend (PersistEntityBackend val)) => FromPreprocess (SqlExpr (Entity val))

Defined in Database.Esqueleto.Internal.Internal

Methods

fromPreprocess :: SqlQuery (PreprocessedFrom (SqlExpr (Entity val)))

(PersistEntity val, BackendCompatible SqlBackend (PersistEntityBackend val)) => FromPreprocess (SqlExpr (Maybe (Entity val)))

Defined in Database.Esqueleto.Internal.Internal

Methods

fromPreprocess :: SqlQuery (PreprocessedFrom (SqlExpr (Maybe (Entity val))))

(FromPreprocess a, FromPreprocess b, IsJoinKind join) => FromPreprocess (join a b)

Defined in Database.Esqueleto.Internal.Internal

Methods

fromPreprocess :: SqlQuery (PreprocessedFrom (join a b))

data EsqueletoError

Exception data type for esqueleto internal errors

Constructors

CompositeKeyErr CompositeKeyError

AliasedValueErr UnexpectedValueError

UnexpectedCaseErr UnexpectedCaseError

SqlBinOpCompositeErr SqlBinOpCompositeError

Instances

Exception EsqueletoError

Defined in Database.Esqueleto.Internal.Internal

Methods

toException :: EsqueletoError -> SomeException

fromException :: SomeException -> Maybe EsqueletoError

displayException :: EsqueletoError -> String

Show EsqueletoError

Defined in Database.Esqueleto.Internal.Internal

Methods

showsPrec :: Int -> EsqueletoError -> ShowS

show :: EsqueletoError -> String

showList :: [EsqueletoError] -> ShowS

data UnexpectedValueError

Constructors

NotError

ToInsertionError

CombineInsertionError

FoldHelpError

SqlCaseError

SqlCastAsError

SqlFunctionError

MakeOnClauseError

MakeExcError

MakeSetError

MakeWhereError

MakeHavingError

FilterWhereAggError

FilterWhereClauseError

Instances

Show UnexpectedValueError

Defined in Database.Esqueleto.Internal.Internal

Methods

showsPrec :: Int -> UnexpectedValueError -> ShowS

show :: UnexpectedValueError -> String

showList :: [UnexpectedValueError] -> ShowS

type CompositeKeyError = UnexpectedValueError

data UnexpectedCaseError

Constructors

EmptySqlExprValueList

MakeFromError

UnsupportedSqlInsertIntoType

InsertionFinalError

NewIdentForError

UnsafeSqlCaseError

OperationNotSupported

NotImplemented

Instances

Show UnexpectedCaseError

Defined in Database.Esqueleto.Internal.Internal

Methods

showsPrec :: Int -> UnexpectedCaseError -> ShowS

show :: UnexpectedCaseError -> String

showList :: [UnexpectedCaseError] -> ShowS

data SqlBinOpCompositeError

Constructors

MismatchingLengthsError

NullPlaceholdersError

DeconstructionError

Instances

Show SqlBinOpCompositeError

Defined in Database.Esqueleto.Internal.Internal

Methods

showsPrec :: Int -> SqlBinOpCompositeError -> ShowS

show :: SqlBinOpCompositeError -> String

showList :: [SqlBinOpCompositeError] -> ShowS

newtype SqlQuery a

SQL backend for esqueleto using SqlPersistT.

Constructors

Q

Fields

• unQ :: WriterT SideData (State IdentState) a

Instances

Applicative SqlQuery

Defined in Database.Esqueleto.Internal.Internal

Methods

pure :: a -> SqlQuery a

(<*>) :: SqlQuery (a -> b) -> SqlQuery a -> SqlQuery b

liftA2 :: (a -> b -> c) -> SqlQuery a -> SqlQuery b -> SqlQuery c

(*>) :: SqlQuery a -> SqlQuery b -> SqlQuery b

(<*) :: SqlQuery a -> SqlQuery b -> SqlQuery a

Functor SqlQuery

Defined in Database.Esqueleto.Internal.Internal

Methods

fmap :: (a -> b) -> SqlQuery a -> SqlQuery b

(<$) :: a -> SqlQuery b -> SqlQuery a

Monad SqlQuery

Defined in Database.Esqueleto.Internal.Internal

Methods

(>>=) :: SqlQuery a -> (a -> SqlQuery b) -> SqlQuery b

(>>) :: SqlQuery a -> SqlQuery b -> SqlQuery b

return :: a -> SqlQuery a

(ToFrom a a', SqlSelect b r, ToAlias b, ToAliasReference b, d ~ (a' :& b)) => DoInnerJoin Lateral a (a' -> SqlQuery b, d -> SqlExpr (Value Bool)) d

Defined in Database.Esqueleto.Experimental.From.Join

Methods

doInnerJoin :: Proxy Lateral -> a -> (a' -> SqlQuery b, d -> SqlExpr (Value Bool)) -> From d

(ToFrom a a', ToMaybe b, d ~ (a' :& ToMaybeT b), SqlSelect b r, ToAlias b, ToAliasReference b) => DoLeftJoin Lateral a (a' -> SqlQuery b, d -> SqlExpr (Value Bool)) d

Defined in Database.Esqueleto.Experimental.From.Join

Methods

doLeftJoin :: Proxy Lateral -> a -> (a' -> SqlQuery b, d -> SqlExpr (Value Bool)) -> From d

(ToFrom a a', SqlSelect b r, ToAlias b, ToAliasReference b) => DoCrossJoin Lateral a (a' -> SqlQuery b) (a' :& b)

Defined in Database.Esqueleto.Experimental.From.Join

Methods

doCrossJoin :: Proxy Lateral -> a -> (a' -> SqlQuery b) -> From (a' :& b)

(SqlSelect a r, ToAlias a, ToAliasReference a) => ToFrom (SubQuery (SqlQuery a)) a

Defined in Database.Esqueleto.Experimental.From

Methods

toFrom :: SubQuery (SqlQuery a) -> From a

(SqlSelect a r, ToAlias a, ToAliasReference a) => ToFrom (SqlQuery a) a

Defined in Database.Esqueleto.Experimental.From

Methods

toFrom :: SqlQuery a -> From a

(SqlSelect a r, ToAlias a, ToAliasReference a) => ToSqlSetOperation (SqlQuery a) a

Defined in Database.Esqueleto.Experimental.From.SqlSetOperation

Methods

toSqlSetOperation :: SqlQuery a -> SqlSetOperation a

ValidOnClause (a -> SqlQuery b)

Defined in Database.Esqueleto.Experimental.From.Join

type SqlEntity ent = (PersistEntity ent, PersistEntityBackend ent ~ SqlBackend)

Constraint synonym for persistent entities whose backend is SqlBackend.

data SideData

Side data written by SqlQuery.

Constructors

SideData

Fields

• sdDistinctClause :: !DistinctClause
• sdFromClause :: ![FromClause]
• sdSetClause :: ![SetClause]
• sdWhereClause :: !WhereClause
• sdGroupByClause :: !GroupByClause
• sdHavingClause :: !HavingClause
• sdOrderByClause :: ![OrderByClause]
• sdLimitClause :: !LimitClause
• sdLockingClause :: !LockingClause
• sdCteClause :: ![CommonTableExpressionClause]

Instances

Monoid SideData

Defined in Database.Esqueleto.Internal.Internal

Methods

mempty :: SideData

mappend :: SideData -> SideData -> SideData

mconcat :: [SideData] -> SideData

Semigroup SideData

Defined in Database.Esqueleto.Internal.Internal

Methods

(<>) :: SideData -> SideData -> SideData

sconcat :: NonEmpty SideData -> SideData

stimes :: Integral b => b -> SideData -> SideData

data DistinctClause

The DISTINCT "clause".

Constructors

DistinctAll

The default, everything.

DistinctStandard

Only DISTINCT, SQL standard.

DistinctOn [SqlExpr DistinctOn]

DISTINCT ON, PostgreSQL extension.

Instances

Monoid DistinctClause

Defined in Database.Esqueleto.Internal.Internal

Methods

mempty :: DistinctClause

mappend :: DistinctClause -> DistinctClause -> DistinctClause

mconcat :: [DistinctClause] -> DistinctClause

Semigroup DistinctClause

Defined in Database.Esqueleto.Internal.Internal

Methods

(<>) :: DistinctClause -> DistinctClause -> DistinctClause

sconcat :: NonEmpty DistinctClause -> DistinctClause

stimes :: Integral b => b -> DistinctClause -> DistinctClause

data FromClause

A part of a FROM clause.

Constructors

FromStart Ident EntityDef

FromJoin FromClause JoinKind FromClause (Maybe (SqlExpr (Value Bool)))

OnClause (SqlExpr (Value Bool))

FromRaw (NeedParens -> IdentInfo -> (Builder, [PersistValue]))

Instances

Show FromClause

Defined in Database.Esqueleto.Internal.Internal

Methods

showsPrec :: Int -> FromClause -> ShowS

show :: FromClause -> String

showList :: [FromClause] -> ShowS

data CommonTableExpressionKind

Constructors

RecursiveCommonTableExpression

NormalCommonTableExpression

Instances

Eq CommonTableExpressionKind

Defined in Database.Esqueleto.Internal.Internal

Methods

(==) :: CommonTableExpressionKind -> CommonTableExpressionKind -> Bool

(/=) :: CommonTableExpressionKind -> CommonTableExpressionKind -> Bool

data CommonTableExpressionClause

Constructors

CommonTableExpressionClause CommonTableExpressionKind Ident (IdentInfo -> (Builder, [PersistValue]))

data SubQueryType

Constructors

NormalSubQuery

LateralSubQuery

Instances

Show SubQueryType

Defined in Database.Esqueleto.Internal.Internal

Methods

showsPrec :: Int -> SubQueryType -> ShowS

show :: SubQueryType -> String

showList :: [SubQueryType] -> ShowS

collectIdents :: FromClause -> Set Ident

newtype SetClause

A part of a SET clause.

Constructors

SetClause (SqlExpr Update)

collectOnClauses :: SqlBackend -> [FromClause] -> Either (SqlExpr (Value Bool)) [FromClause]

Collect OnClauses on FromJoins. Returns the first unmatched OnClauses data on error. Returns a list without OnClauses on success.

data WhereClause

A complete WHERE clause.

Constructors

Where (SqlExpr (Value Bool))

NoWhere

Instances

Monoid WhereClause

Defined in Database.Esqueleto.Internal.Internal

Methods

mempty :: WhereClause

mappend :: WhereClause -> WhereClause -> WhereClause

mconcat :: [WhereClause] -> WhereClause

Semigroup WhereClause

Defined in Database.Esqueleto.Internal.Internal

Methods

(<>) :: WhereClause -> WhereClause -> WhereClause

sconcat :: NonEmpty WhereClause -> WhereClause

stimes :: Integral b => b -> WhereClause -> WhereClause

newtype GroupByClause

A GROUP BY clause.

Constructors

GroupBy [SomeValue]

Instances

Monoid GroupByClause

Defined in Database.Esqueleto.Internal.Internal

Methods

mempty :: GroupByClause

mappend :: GroupByClause -> GroupByClause -> GroupByClause

mconcat :: [GroupByClause] -> GroupByClause

Semigroup GroupByClause

Defined in Database.Esqueleto.Internal.Internal

Methods

(<>) :: GroupByClause -> GroupByClause -> GroupByClause

sconcat :: NonEmpty GroupByClause -> GroupByClause

stimes :: Integral b => b -> GroupByClause -> GroupByClause

type HavingClause = WhereClause

A HAVING cause.

type OrderByClause = SqlExpr OrderBy

A ORDER BY clause.

data LimitClause

A LIMIT clause.

Constructors

Limit (Maybe Int64) (Maybe Int64)

Instances

Monoid LimitClause

Defined in Database.Esqueleto.Internal.Internal

Methods

mempty :: LimitClause

mappend :: LimitClause -> LimitClause -> LimitClause

mconcat :: [LimitClause] -> LimitClause

Semigroup LimitClause

Defined in Database.Esqueleto.Internal.Internal

Methods

(<>) :: LimitClause -> LimitClause -> LimitClause

sconcat :: NonEmpty LimitClause -> LimitClause

stimes :: Integral b => b -> LimitClause -> LimitClause

Eq LimitClause

Defined in Database.Esqueleto.Internal.Internal

Methods

(==) :: LimitClause -> LimitClause -> Bool

(/=) :: LimitClause -> LimitClause -> Bool

type LockingClause = Last LockingKind

A locking clause.

newtype Ident

Identifier used for table names.

Constructors

I Text

Instances

Show Ident

Defined in Database.Esqueleto.Internal.Internal

Methods

showsPrec :: Int -> Ident -> ShowS

show :: Ident -> String

showList :: [Ident] -> ShowS

Eq Ident

Defined in Database.Esqueleto.Internal.Internal

Methods

(==) :: Ident -> Ident -> Bool

(/=) :: Ident -> Ident -> Bool

Ord Ident

Defined in Database.Esqueleto.Internal.Internal

Methods

compare :: Ident -> Ident -> Ordering

(<) :: Ident -> Ident -> Bool

(<=) :: Ident -> Ident -> Bool

(>) :: Ident -> Ident -> Bool

(>=) :: Ident -> Ident -> Bool

max :: Ident -> Ident -> Ident

min :: Ident -> Ident -> Ident

newtype IdentState

List of identifiers already in use and supply of temporary identifiers.

Constructors

IdentState

Fields

• inUse :: HashSet Text

initialIdentState :: IdentState

newIdentFor :: DBName -> SqlQuery Ident

Create a fresh Ident. If possible, use the given DBName.

type IdentInfo = (SqlBackend, IdentState)

Information needed to escape and use identifiers.

useIdent :: IdentInfo -> Ident -> Builder

Use an identifier.

data SqlExprMeta

Constructors

SqlExprMeta

Fields

• sqlExprMetaCompositeFields :: Maybe (IdentInfo -> [Builder])
• sqlExprMetaAlias :: Maybe Ident
• sqlExprMetaIsReference :: Bool

noMeta :: SqlExprMeta

Empty SqlExprMeta if you are constructing an ERaw probably use this for your meta

hasCompositeKeyMeta :: SqlExprMeta -> Bool

Does this meta contain values for composite fields. This field is field out for composite key values

entityAsValue :: SqlExpr (Entity val) -> SqlExpr (Value (Entity val))

entityAsValueMaybe :: SqlExpr (Maybe (Entity val)) -> SqlExpr (Value (Maybe (Entity val)))

data SqlExpr a

An expression on the SQL backend.

Raw expression: Contains a SqlExprMeta and a function for building the expr. It recieves a parameter telling it whether it is in a parenthesized context, and takes information about the SQL connection (mainly for escaping names) and returns both an string (Builder) and a list of values to be interpolated by the SQL backend.

Constructors

ERaw SqlExprMeta (NeedParens -> IdentInfo -> (Builder, [PersistValue]))

Instances

(PersistEntity rec, PersistField typ, SymbolToField sym rec typ) => HasField (sym :: Symbol) (SqlExpr (Entity rec)) (SqlExpr (Value typ))

This instance allows you to use record.field notation with GHC 9.2's OverloadedRecordDot extension.

Example:

-- persistent model:
BlogPost
    authorId     PersonId
    title        Text

-- query:
select $ do
    bp <- from $ table @BlogPost
    pure $ bp.title

This is exactly equivalent to the following:

blogPost :: SqlExpr (Entity BlogPost)

blogPost ^. BlogPostTitle
blogPost ^. #title
blogPost.title

There's another instance defined on SqlExpr (Entity (Maybe rec)), which allows you to project from a LEFT JOINed entity.

Since: 3.5.4.0

Defined in Database.Esqueleto.Internal.Internal

Methods

getField :: SqlExpr (Entity rec) -> SqlExpr (Value typ)

(PersistEntity rec, PersistField typ, SymbolToField sym rec typ) => HasField (sym :: Symbol) (SqlExpr (Maybe (Entity rec))) (SqlExpr (Value (Maybe typ)))

This instance allows you to use record.field notation with GC 9.2's OverloadedRecordDot extension.

Example:

-- persistent model:
Person
    name         Text

BlogPost
    title        Text
    authorId     PersonId

-- query:

select $ do
    (p :& bp) <- from $
        table Person
        leftJoin table BlogPost
        on do
            \(p :& bp) ->
                just p.id ==. bp.authorId
    pure (p.name, bp.title)

The following forms are all equivalent:

blogPost :: SqlExpr (Maybe (Entity BlogPost))

blogPost ?. BlogPostTitle
blogPost ?. #title
blogPost.title

Since: 3.5.4.0

Defined in Database.Esqueleto.Internal.Internal

Methods

getField :: SqlExpr (Maybe (Entity rec)) -> SqlExpr (Value (Maybe typ))

(ToFrom a a', SqlSelect b r, ToAlias b, ToAliasReference b, d ~ (a' :& b)) => DoInnerJoin Lateral a (a' -> SqlQuery b, d -> SqlExpr (Value Bool)) d

Defined in Database.Esqueleto.Experimental.From.Join

Methods

doInnerJoin :: Proxy Lateral -> a -> (a' -> SqlQuery b, d -> SqlExpr (Value Bool)) -> From d

(ToFrom a a', ToMaybe b, d ~ (a' :& ToMaybeT b), SqlSelect b r, ToAlias b, ToAliasReference b) => DoLeftJoin Lateral a (a' -> SqlQuery b, d -> SqlExpr (Value Bool)) d

Defined in Database.Esqueleto.Experimental.From.Join

Methods

doLeftJoin :: Proxy Lateral -> a -> (a' -> SqlQuery b, d -> SqlExpr (Value Bool)) -> From d

ToAlias (SqlExpr (Value a))

Defined in Database.Esqueleto.Experimental.ToAlias

Methods

toAlias :: SqlExpr (Value a) -> SqlQuery (SqlExpr (Value a))

ToAlias (SqlExpr (Entity a))

Defined in Database.Esqueleto.Experimental.ToAlias

Methods

toAlias :: SqlExpr (Entity a) -> SqlQuery (SqlExpr (Entity a))

ToAlias (SqlExpr (Maybe (Entity a)))

Defined in Database.Esqueleto.Experimental.ToAlias

Methods

toAlias :: SqlExpr (Maybe (Entity a)) -> SqlQuery (SqlExpr (Maybe (Entity a)))

ToAliasReference (SqlExpr (Value a))

Defined in Database.Esqueleto.Experimental.ToAliasReference

Methods

toAliasReference :: Ident -> SqlExpr (Value a) -> SqlQuery (SqlExpr (Value a))

ToAliasReference (SqlExpr (Entity a))

Defined in Database.Esqueleto.Experimental.ToAliasReference

Methods

toAliasReference :: Ident -> SqlExpr (Entity a) -> SqlQuery (SqlExpr (Entity a))

ToAliasReference (SqlExpr (Maybe (Entity a)))

Defined in Database.Esqueleto.Experimental.ToAliasReference

Methods

toAliasReference :: Ident -> SqlExpr (Maybe (Entity a)) -> SqlQuery (SqlExpr (Maybe (Entity a)))

ToMaybe (SqlExpr (Value a))

Defined in Database.Esqueleto.Experimental.ToMaybe

Associated Types

type ToMaybeT (SqlExpr (Value a))

Methods

toMaybe :: SqlExpr (Value a) -> ToMaybeT (SqlExpr (Value a))

ToMaybe (SqlExpr (Entity a))

Defined in Database.Esqueleto.Experimental.ToMaybe

Associated Types

type ToMaybeT (SqlExpr (Entity a))

Methods

toMaybe :: SqlExpr (Entity a) -> ToMaybeT (SqlExpr (Entity a))

ToMaybe (SqlExpr (Maybe a))

Defined in Database.Esqueleto.Experimental.ToMaybe

Associated Types

type ToMaybeT (SqlExpr (Maybe a))

Methods

toMaybe :: SqlExpr (Maybe a) -> ToMaybeT (SqlExpr (Maybe a))

FromPreprocess (SqlExpr (Entity val)) => From (SqlExpr (Entity val))

Defined in Database.Esqueleto.Internal.Internal

Methods

from_ :: SqlQuery (SqlExpr (Entity val))

FromPreprocess (SqlExpr (Maybe (Entity val))) => From (SqlExpr (Maybe (Entity val)))

Defined in Database.Esqueleto.Internal.Internal

Methods

from_ :: SqlQuery (SqlExpr (Maybe (Entity val)))

(PersistEntity val, BackendCompatible SqlBackend (PersistEntityBackend val)) => FromPreprocess (SqlExpr (Entity val))

Defined in Database.Esqueleto.Internal.Internal

Methods

fromPreprocess :: SqlQuery (PreprocessedFrom (SqlExpr (Entity val)))

(PersistEntity val, BackendCompatible SqlBackend (PersistEntityBackend val)) => FromPreprocess (SqlExpr (Maybe (Entity val)))

Defined in Database.Esqueleto.Internal.Internal

Methods

fromPreprocess :: SqlQuery (PreprocessedFrom (SqlExpr (Maybe (Entity val))))

ToSomeValues (SqlExpr (Value a))

Defined in Database.Esqueleto.Internal.Internal

Methods

toSomeValues :: SqlExpr (Value a) -> [SomeValue]

a ~ Value b => UnsafeSqlFunctionArgument (SqlExpr a)

Defined in Database.Esqueleto.Internal.Internal

Methods

toArgList :: SqlExpr a -> [SqlExpr (Value ())]

PersistEntity ent => ToFrom (Table ent) (SqlExpr (Entity ent))

Defined in Database.Esqueleto.Experimental.From

Methods

toFrom :: Table ent -> From (SqlExpr (Entity ent))

PersistEntity e => SqlSelect (SqlExpr (Insertion e)) (Insertion e)

INSERT INTO hack.

Defined in Database.Esqueleto.Internal.Internal

Methods

sqlSelectCols :: IdentInfo -> SqlExpr (Insertion e) -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy (SqlExpr (Insertion e)) -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text (Insertion e)

sqlInsertInto :: IdentInfo -> SqlExpr (Insertion e) -> (Builder, [PersistValue])

PersistField a => SqlSelect (SqlExpr (Value a)) (Value a)

You may return any single value (i.e. a single column) from a select query.

Defined in Database.Esqueleto.Internal.Internal

Methods

sqlSelectCols :: IdentInfo -> SqlExpr (Value a) -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy (SqlExpr (Value a)) -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text (Value a)

sqlInsertInto :: IdentInfo -> SqlExpr (Value a) -> (Builder, [PersistValue])

PersistEntity a => SqlSelect (SqlExpr (Entity a)) (Entity a)

You may return an Entity from a select query.

Defined in Database.Esqueleto.Internal.Internal

Methods

sqlSelectCols :: IdentInfo -> SqlExpr (Entity a) -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy (SqlExpr (Entity a)) -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text (Entity a)

sqlInsertInto :: IdentInfo -> SqlExpr (Entity a) -> (Builder, [PersistValue])

PersistEntity a => SqlSelect (SqlExpr (Maybe (Entity a))) (Maybe (Entity a))

You may return a possibly-NULL Entity from a select query.

Defined in Database.Esqueleto.Internal.Internal

Methods

sqlSelectCols :: IdentInfo -> SqlExpr (Maybe (Entity a)) -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy (SqlExpr (Maybe (Entity a))) -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text (Maybe (Entity a))

sqlInsertInto :: IdentInfo -> SqlExpr (Maybe (Entity a)) -> (Builder, [PersistValue])

type ToMaybeT (SqlExpr (Value a))

Defined in Database.Esqueleto.Experimental.ToMaybe

type ToMaybeT (SqlExpr (Value a)) = SqlExpr (Value (Maybe (Nullable a)))

type ToMaybeT (SqlExpr (Entity a))

Defined in Database.Esqueleto.Experimental.ToMaybe

type ToMaybeT (SqlExpr (Entity a)) = SqlExpr (Maybe (Entity a))

type ToMaybeT (SqlExpr (Maybe a))

Defined in Database.Esqueleto.Experimental.ToMaybe

type ToMaybeT (SqlExpr (Maybe a)) = SqlExpr (Maybe a)

data PreprocessedFrom a

Data type to support from hack

Constructors

PreprocessedFrom a FromClause

data InsertFinal

Phantom type used to mark a INSERT INTO query.

data NeedParens

Constructors

Parens

Never

Instances

Eq NeedParens

Defined in Database.Esqueleto.Internal.Internal

Methods

(==) :: NeedParens -> NeedParens -> Bool

(/=) :: NeedParens -> NeedParens -> Bool

parensM :: NeedParens -> Builder -> Builder

data OrderByType

Constructors

ASC

DESC

fieldName :: (PersistEntity val, PersistField typ) => IdentInfo -> EntityField val typ -> Builder

setAux :: (PersistEntity val, PersistField typ) => EntityField val typ -> (SqlExpr (Entity val) -> SqlExpr (Value typ)) -> SqlExpr (Entity val) -> SqlExpr Update

sub :: PersistField a => Mode -> SqlQuery (SqlExpr (Value a)) -> SqlExpr (Value a)

fromDBName :: IdentInfo -> DBName -> Builder

existsHelper :: SqlQuery () -> SqlExpr (Value Bool)

unsafeSqlCase :: PersistField a => [(SqlExpr (Value Bool), SqlExpr (Value a))] -> SqlExpr (Value a) -> SqlExpr (Value a)

(Internal) Create a case statement.

Since: 2.1.1

unsafeSqlBinOp :: Builder -> SqlExpr (Value a) -> SqlExpr (Value b) -> SqlExpr (Value c)

(Internal) Create a custom binary operator. You should not use this function directly since its type is very general, you should always use it with an explicit type signature. For example:

(==.) :: SqlExpr (Value a) -> SqlExpr (Value a) -> SqlExpr (Value Bool)
(==.) = unsafeSqlBinOp " = "

In the example above, we constraint the arguments to be of the same type and constraint the result to be a boolean value.

unsafeSqlBinOpComposite :: Builder -> Builder -> SqlExpr (Value a) -> SqlExpr (Value b) -> SqlExpr (Value c)

Similar to unsafeSqlBinOp, but may also be applied to composite keys. Uses the operator given as the second argument whenever applied to composite keys.

Usage example:

(==.) :: SqlExpr (Value a) -> SqlExpr (Value a) -> SqlExpr (Value Bool)
(==.) = unsafeSqlBinOpComposite " = " " AND "

Persistent has a hack for implementing composite keys (see ECompositeKey doc for more details), so we're forced to use a hack here as well. We deconstruct ERaw values based on two rules:

• If it is a single placeholder, then it's assumed to be coming from a PersistList and thus its components are separated so that they may be applied to a composite key.
• If it is not a single placeholder, then it's assumed to be a foreign (composite or not) key, so we enforce that it has no placeholders and split it on the commas.

unsafeSqlValue :: Builder -> SqlExpr (Value a)

(Internal) A raw SQL value. The same warning from unsafeSqlBinOp applies to this function as well.

unsafeSqlEntity :: PersistEntity ent => Ident -> SqlExpr (Entity ent)

valueToFunctionArg :: IdentInfo -> SqlExpr (Value a) -> (Builder, [PersistValue])

unsafeSqlFunction :: UnsafeSqlFunctionArgument a => Builder -> a -> SqlExpr (Value b)

(Internal) A raw SQL function. Once again, the same warning from unsafeSqlBinOp applies to this function as well.

unsafeSqlExtractSubField :: UnsafeSqlFunctionArgument a => Builder -> a -> SqlExpr (Value b)

(Internal) An unsafe SQL function to extract a subfield from a compound field, e.g. datetime. See unsafeSqlBinOp for warnings.

Since: 1.3.6.

unsafeSqlFunctionParens :: UnsafeSqlFunctionArgument a => Builder -> a -> SqlExpr (Value b)

(Internal) A raw SQL function. Preserves parentheses around arguments. See unsafeSqlBinOp for warnings.

unsafeSqlCastAs :: Text -> SqlExpr (Value a) -> SqlExpr (Value b)

(Internal) An explicit SQL type cast using CAST(value as type). See unsafeSqlBinOp for warnings.

class UnsafeSqlFunctionArgument a where

(Internal) This class allows unsafeSqlFunction to work with different numbers of arguments; specifically it allows providing arguments to a sql function via an n-tuple of SqlExpr (Value _) values, which are not all necessarily required to be the same type. There are instances for up to 10-tuples, but for sql functions which take more than 10 arguments, you can also nest tuples, as e.g. toArgList ((a,b),(c,d)) is the same as toArgList (a,b,c,d).

Methods

toArgList :: a -> [SqlExpr (Value ())]

Instances

UnsafeSqlFunctionArgument ()

Useful for 0-argument functions, like now in Postgresql.

Since: 3.2.1

Defined in Database.Esqueleto.Internal.Internal

Methods

toArgList :: () -> [SqlExpr (Value ())]

a ~ Value b => UnsafeSqlFunctionArgument (SqlExpr a)

Defined in Database.Esqueleto.Internal.Internal

Methods

toArgList :: SqlExpr a -> [SqlExpr (Value ())]

UnsafeSqlFunctionArgument a => UnsafeSqlFunctionArgument [a]

Defined in Database.Esqueleto.Internal.Internal

Methods

toArgList :: [a] -> [SqlExpr (Value ())]

(UnsafeSqlFunctionArgument a, UnsafeSqlFunctionArgument b) => UnsafeSqlFunctionArgument (a, b)

Defined in Database.Esqueleto.Internal.Internal

Methods

toArgList :: (a, b) -> [SqlExpr (Value ())]

(UnsafeSqlFunctionArgument a, UnsafeSqlFunctionArgument b, UnsafeSqlFunctionArgument c) => UnsafeSqlFunctionArgument (a, b, c)

Defined in Database.Esqueleto.Internal.Internal

Methods

toArgList :: (a, b, c) -> [SqlExpr (Value ())]

(UnsafeSqlFunctionArgument a, UnsafeSqlFunctionArgument b, UnsafeSqlFunctionArgument c, UnsafeSqlFunctionArgument d) => UnsafeSqlFunctionArgument (a, b, c, d)

Defined in Database.Esqueleto.Internal.Internal

Methods

toArgList :: (a, b, c, d) -> [SqlExpr (Value ())]

(UnsafeSqlFunctionArgument a, UnsafeSqlFunctionArgument b, UnsafeSqlFunctionArgument c, UnsafeSqlFunctionArgument d, UnsafeSqlFunctionArgument e) => UnsafeSqlFunctionArgument (a, b, c, d, e)

Since: 3.2.3

Defined in Database.Esqueleto.Internal.Internal

Methods

toArgList :: (a, b, c, d, e) -> [SqlExpr (Value ())]

(UnsafeSqlFunctionArgument a, UnsafeSqlFunctionArgument b, UnsafeSqlFunctionArgument c, UnsafeSqlFunctionArgument d, UnsafeSqlFunctionArgument e, UnsafeSqlFunctionArgument f) => UnsafeSqlFunctionArgument (a, b, c, d, e, f)

Since: 3.2.3

Defined in Database.Esqueleto.Internal.Internal

Methods

toArgList :: (a, b, c, d, e, f) -> [SqlExpr (Value ())]

(UnsafeSqlFunctionArgument a, UnsafeSqlFunctionArgument b, UnsafeSqlFunctionArgument c, UnsafeSqlFunctionArgument d, UnsafeSqlFunctionArgument e, UnsafeSqlFunctionArgument f, UnsafeSqlFunctionArgument g) => UnsafeSqlFunctionArgument (a, b, c, d, e, f, g)

Since: 3.2.3

Defined in Database.Esqueleto.Internal.Internal

Methods

toArgList :: (a, b, c, d, e, f, g) -> [SqlExpr (Value ())]

(UnsafeSqlFunctionArgument a, UnsafeSqlFunctionArgument b, UnsafeSqlFunctionArgument c, UnsafeSqlFunctionArgument d, UnsafeSqlFunctionArgument e, UnsafeSqlFunctionArgument f, UnsafeSqlFunctionArgument g, UnsafeSqlFunctionArgument h) => UnsafeSqlFunctionArgument (a, b, c, d, e, f, g, h)

Since: 3.2.3

Defined in Database.Esqueleto.Internal.Internal

Methods

toArgList :: (a, b, c, d, e, f, g, h) -> [SqlExpr (Value ())]

(UnsafeSqlFunctionArgument a, UnsafeSqlFunctionArgument b, UnsafeSqlFunctionArgument c, UnsafeSqlFunctionArgument d, UnsafeSqlFunctionArgument e, UnsafeSqlFunctionArgument f, UnsafeSqlFunctionArgument g, UnsafeSqlFunctionArgument h, UnsafeSqlFunctionArgument i) => UnsafeSqlFunctionArgument (a, b, c, d, e, f, g, h, i)

Since: 3.2.3

Defined in Database.Esqueleto.Internal.Internal

Methods

toArgList :: (a, b, c, d, e, f, g, h, i) -> [SqlExpr (Value ())]

(UnsafeSqlFunctionArgument a, UnsafeSqlFunctionArgument b, UnsafeSqlFunctionArgument c, UnsafeSqlFunctionArgument d, UnsafeSqlFunctionArgument e, UnsafeSqlFunctionArgument f, UnsafeSqlFunctionArgument g, UnsafeSqlFunctionArgument h, UnsafeSqlFunctionArgument i, UnsafeSqlFunctionArgument j) => UnsafeSqlFunctionArgument (a, b, c, d, e, f, g, h, i, j)

Since: 3.2.3

Defined in Database.Esqueleto.Internal.Internal

Methods

toArgList :: (a, b, c, d, e, f, g, h, i, j) -> [SqlExpr (Value ())]

veryUnsafeCoerceSqlExprValue :: SqlExpr (Value a) -> SqlExpr (Value b)

(Internal) Coerce a value's type from 'SqlExpr (Value a)' to 'SqlExpr (Value b)'. You should not use this function unless you know what you're doing!

veryUnsafeCoerceSqlExprValueList :: SqlExpr (ValueList a) -> SqlExpr (Value a)

(Internal) Coerce a value's type from 'SqlExpr (ValueList a)' to 'SqlExpr (Value a)'. Does not work with empty lists.

rawSelectSource :: (SqlSelect a r, MonadIO m1, MonadIO m2, SqlBackendCanRead backend) => Mode -> SqlQuery a -> ReaderT backend m1 (Acquire (ConduitT () r m2 ()))

(Internal) Execute an esqueleto SELECT SqlQuery inside persistent's SqlPersistT monad.

selectSource :: (SqlSelect a r, BackendCompatible SqlBackend backend, IsPersistBackend backend, PersistQueryRead backend, PersistStoreRead backend, PersistUniqueRead backend, MonadResource m) => SqlQuery a -> ConduitT () r (ReaderT backend m) ()

Execute an esqueleto SELECT query inside persistent's SqlPersistT monad and return a Source of rows.

select :: (SqlSelect a r, MonadIO m, SqlBackendCanRead backend) => SqlQuery a -> ReaderT backend m [r]

Execute an esqueleto SELECT query inside persistent's SqlPersistT monad and return a list of rows.

We've seen that from has some magic about which kinds of things you may bring into scope. This select function also has some magic for which kinds of things you may bring back to Haskell-land by using SqlQuery's return:

• You may return a SqlExpr (Entity v) for an entity v (i.e., like the * in SQL), which is then returned to Haskell-land as just Entity v.
• You may return a SqlExpr (Maybe (Entity v)) for an entity v that may be NULL, which is then returned to Haskell-land as Maybe (Entity v). Used for OUTER JOINs.
• You may return a SqlExpr (Value t) for a value t (i.e., a single column), where t is any instance of PersistField, which is then returned to Haskell-land as Value t. You may use Value to return projections of an Entity (see (^.) and (?.)) or to return any other value calculated on the query (e.g., countRows or subSelect).

The SqlSelect a r class has functional dependencies that allow type information to flow both from a to r and vice-versa. This means that you'll almost never have to give any type signatures for esqueleto queries. For example, the query select $ from $ \p -> return p alone is ambiguous, but in the context of

do ps <- select $
         from $ \p ->
         return p
   liftIO $ mapM_ (putStrLn . personName . entityVal) ps

we are able to infer from that single personName . entityVal function composition that the p inside the query is of type SqlExpr (Entity Person).

selectOne :: (SqlSelect a r, MonadIO m, SqlBackendCanRead backend) => SqlQuery a -> ReaderT backend m (Maybe r)

Execute an esqueleto SELECT query inside persistent's SqlPersistT monad and return the first entry wrapped in a Maybe. @since 3.5.1.0

Example usage

firstPerson :: MonadIO m => SqlPersistT m (Maybe (Entity Person))
firstPerson =
 selectOne $ do
     person <- from $ table @Person
     return person

The above query is equivalent to a select combined with limit but you would still have to transform the results from a list:

firstPerson :: MonadIO m => SqlPersistT m [Entity Person]
firstPerson =
 select $ do
     person <- from $ table @Person
     limit 1
     return person

runSource :: Monad m => ConduitT () r (ReaderT backend m) () -> ReaderT backend m [r]

(Internal) Run a Source of rows.

rawEsqueleto :: (MonadIO m, SqlSelect a r, BackendCompatible SqlBackend backend) => Mode -> SqlQuery a -> ReaderT backend m Int64

(Internal) Execute an esqueleto statement inside persistent's SqlPersistT monad.

delete :: (MonadIO m, SqlBackendCanWrite backend) => SqlQuery () -> ReaderT backend m ()

Execute an esqueleto DELETE query inside persistent's SqlPersistT monad. Note that currently there are no type checks for statements that should not appear on a DELETE query.

Example of usage:

delete $
from $ \appointment ->
where_ (appointment ^. AppointmentDate <. val now)

Unlike select, there is a useful way of using delete that will lead to type ambiguities. If you want to delete all rows (i.e., no where_ clause), you'll have to use a type signature:

delete $
from $ \(appointment :: SqlExpr (Entity Appointment)) ->
return ()

Database.Esqueleto.Experimental:

 delete $ do
   userFeature <- from $ table @UserFeature
   where_ ((userFeature ^. UserFeatureFeature) notIn valList allKnownFeatureFlags)

deleteCount :: (MonadIO m, SqlBackendCanWrite backend) => SqlQuery () -> ReaderT backend m Int64

Same as delete, but returns the number of rows affected.

update :: (MonadIO m, PersistEntity val, BackendCompatible SqlBackend (PersistEntityBackend val), SqlBackendCanWrite backend) => (SqlExpr (Entity val) -> SqlQuery ()) -> ReaderT backend m ()

Execute an esqueleto UPDATE query inside persistent's SqlPersistT monad. Note that currently there are no type checks for statements that should not appear on a UPDATE query.

Example of usage:

update $ \p -> do
set p [ PersonAge =. just (val thisYear) -. p ^. PersonBorn ]
where_ $ isNothing (p ^. PersonAge)

updateCount :: (MonadIO m, PersistEntity val, BackendCompatible SqlBackend (PersistEntityBackend val), SqlBackendCanWrite backend) => (SqlExpr (Entity val) -> SqlQuery ()) -> ReaderT backend m Int64

Same as update, but returns the number of rows affected.

builderToText :: Builder -> Text

toRawSql :: (SqlSelect a r, BackendCompatible SqlBackend backend) => Mode -> (backend, IdentState) -> SqlQuery a -> (Builder, [PersistValue])

(Internal) Pretty prints a SqlQuery into a SQL query.

Note: if you're curious about the SQL query being generated by esqueleto, instead of manually using this function (which is possible but tedious), see the renderQueryToText function (along with renderQuerySelect, renderQueryUpdate, etc).

renderQueryToText

Arguments

:: (SqlSelect a r, BackendCompatible SqlBackend backend, Monad m)

=> Mode

Whether to render as an SELECT, DELETE, etc.

-> SqlQuery a

The SQL query you want to render.

-> ReaderT backend m (Text, [PersistValue])

Renders a SqlQuery into a Text value along with the list of PersistValues that would be supplied to the database for ? placeholders.

You must ensure that the Mode you pass to this function corresponds with the actual SqlQuery. If you pass a query that uses incompatible features (like an INSERT statement with a SELECT mode) then you'll get a weird result.

Since: 3.1.1

renderQuerySelect

Arguments

:: (SqlSelect a r, BackendCompatible SqlBackend backend, Monad m)

=> SqlQuery a

The SQL query you want to render.

-> ReaderT backend m (Text, [PersistValue])

Renders a SqlQuery into a Text value along with the list of PersistValues that would be supplied to the database for ? placeholders.

Since: 3.1.1

renderQueryDelete

Arguments

:: (SqlSelect a r, BackendCompatible SqlBackend backend, Monad m)

=> SqlQuery a

The SQL query you want to render.

-> ReaderT backend m (Text, [PersistValue])

Renders a SqlQuery into a Text value along with the list of PersistValues that would be supplied to the database for ? placeholders.

Since: 3.1.1

renderQueryUpdate

Arguments

:: (SqlSelect a r, BackendCompatible SqlBackend backend, Monad m)

=> SqlQuery a

The SQL query you want to render.

-> ReaderT backend m (Text, [PersistValue])

Renders a SqlQuery into a Text value along with the list of PersistValues that would be supplied to the database for ? placeholders.

Since: 3.1.1

renderQueryInsertInto

Arguments

:: (SqlSelect a r, BackendCompatible SqlBackend backend, Monad m)

=> SqlQuery a

The SQL query you want to render.

-> ReaderT backend m (Text, [PersistValue])

Renders a SqlQuery into a Text value along with the list of PersistValues that would be supplied to the database for ? placeholders.

Since: 3.1.1

data Mode

(Internal) Mode of query being converted by toRawSql.

Constructors

SELECT

DELETE

UPDATE

INSERT_INTO

uncommas :: [Builder] -> Builder

intersperseB :: Builder -> [Builder] -> Builder

uncommas' :: Monoid a => [(Builder, a)] -> (Builder, a)

makeCte :: IdentInfo -> [CommonTableExpressionClause] -> (Builder, [PersistValue])

makeInsertInto :: SqlSelect a r => IdentInfo -> Mode -> a -> (Builder, [PersistValue])

makeSelect :: SqlSelect a r => IdentInfo -> Mode -> DistinctClause -> a -> (Builder, [PersistValue])

makeFrom :: IdentInfo -> Mode -> [FromClause] -> (Builder, [PersistValue])

makeSet :: IdentInfo -> [SetClause] -> (Builder, [PersistValue])

makeWhere :: IdentInfo -> WhereClause -> (Builder, [PersistValue])

makeGroupBy :: IdentInfo -> GroupByClause -> (Builder, [PersistValue])

makeHaving :: IdentInfo -> WhereClause -> (Builder, [PersistValue])

makeOrderByNoNewline :: IdentInfo -> [OrderByClause] -> (Builder, [PersistValue])

makeOrderBy :: IdentInfo -> [OrderByClause] -> (Builder, [PersistValue])

makeLimit :: IdentInfo -> LimitClause -> (Builder, [PersistValue])

makeLocking :: LockingClause -> (Builder, [PersistValue])

parens :: Builder -> Builder

aliasedEntityColumnIdent :: Ident -> FieldDef -> Ident

aliasedColumnName :: Ident -> IdentInfo -> Text -> Builder

class SqlSelect a r | a -> r, r -> a where

(Internal) Class for mapping results coming from SqlQuery into actual results.

This looks very similar to RawSql, and it is! However, there are some crucial differences and ultimately they're different classes.

Minimal complete definition

sqlSelectCols, sqlSelectColCount, sqlSelectProcessRow

Methods

sqlSelectCols :: IdentInfo -> a -> (Builder, [PersistValue])

Creates the variable part of the SELECT query and returns the list of PersistValues that will be given to rawQuery.

sqlSelectColCount :: Proxy a -> Int

Number of columns that will be consumed.

sqlSelectProcessRow :: [PersistValue] -> Either Text r

Transform a row of the result into the data type.

sqlInsertInto :: IdentInfo -> a -> (Builder, [PersistValue])

Create INSERT INTO clause instead.

Instances

SqlSelect () ()

Not useful for select, but used for update and delete.

Defined in Database.Esqueleto.Internal.Internal

Methods

sqlSelectCols :: IdentInfo -> () -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy () -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text ()

sqlInsertInto :: IdentInfo -> () -> (Builder, [PersistValue])

PersistEntity e => SqlSelect (SqlExpr (Insertion e)) (Insertion e)

INSERT INTO hack.

Defined in Database.Esqueleto.Internal.Internal

Methods

sqlSelectCols :: IdentInfo -> SqlExpr (Insertion e) -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy (SqlExpr (Insertion e)) -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text (Insertion e)

sqlInsertInto :: IdentInfo -> SqlExpr (Insertion e) -> (Builder, [PersistValue])

PersistField a => SqlSelect (SqlExpr (Value a)) (Value a)

You may return any single value (i.e. a single column) from a select query.

Defined in Database.Esqueleto.Internal.Internal

Methods

sqlSelectCols :: IdentInfo -> SqlExpr (Value a) -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy (SqlExpr (Value a)) -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text (Value a)

sqlInsertInto :: IdentInfo -> SqlExpr (Value a) -> (Builder, [PersistValue])

PersistEntity a => SqlSelect (SqlExpr (Entity a)) (Entity a)

You may return an Entity from a select query.

Defined in Database.Esqueleto.Internal.Internal

Methods

sqlSelectCols :: IdentInfo -> SqlExpr (Entity a) -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy (SqlExpr (Entity a)) -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text (Entity a)

sqlInsertInto :: IdentInfo -> SqlExpr (Entity a) -> (Builder, [PersistValue])

PersistEntity a => SqlSelect (SqlExpr (Maybe (Entity a))) (Maybe (Entity a))

You may return a possibly-NULL Entity from a select query.

Defined in Database.Esqueleto.Internal.Internal

Methods

sqlSelectCols :: IdentInfo -> SqlExpr (Maybe (Entity a)) -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy (SqlExpr (Maybe (Entity a))) -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text (Maybe (Entity a))

sqlInsertInto :: IdentInfo -> SqlExpr (Maybe (Entity a)) -> (Builder, [PersistValue])

(SqlSelect a ra, SqlSelect b rb) => SqlSelect (a :& b) (ra :& rb)

You may return joined values from a select query - this is identical to the tuple instance, but is provided for convenience.

Since: 3.5.2.0

Defined in Database.Esqueleto.Experimental.From.Join

Methods

sqlSelectCols :: IdentInfo -> (a :& b) -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy (a :& b) -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text (ra :& rb)

sqlInsertInto :: IdentInfo -> (a :& b) -> (Builder, [PersistValue])

(SqlSelect a ra, SqlSelect b rb) => SqlSelect (a, b) (ra, rb)

You may return tuples (up to 16-tuples) and tuples of tuples from a select query.

Defined in Database.Esqueleto.Internal.Internal

Methods

sqlSelectCols :: IdentInfo -> (a, b) -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy (a, b) -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text (ra, rb)

sqlInsertInto :: IdentInfo -> (a, b) -> (Builder, [PersistValue])

(SqlSelect a ra, SqlSelect b rb, SqlSelect c rc) => SqlSelect (a, b, c) (ra, rb, rc)

Defined in Database.Esqueleto.Internal.Internal

Methods

sqlSelectCols :: IdentInfo -> (a, b, c) -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy (a, b, c) -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text (ra, rb, rc)

sqlInsertInto :: IdentInfo -> (a, b, c) -> (Builder, [PersistValue])

(SqlSelect a ra, SqlSelect b rb, SqlSelect c rc, SqlSelect d rd) => SqlSelect (a, b, c, d) (ra, rb, rc, rd)

Defined in Database.Esqueleto.Internal.Internal

Methods

sqlSelectCols :: IdentInfo -> (a, b, c, d) -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy (a, b, c, d) -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text (ra, rb, rc, rd)

sqlInsertInto :: IdentInfo -> (a, b, c, d) -> (Builder, [PersistValue])

(SqlSelect a ra, SqlSelect b rb, SqlSelect c rc, SqlSelect d rd, SqlSelect e re) => SqlSelect (a, b, c, d, e) (ra, rb, rc, rd, re)

Defined in Database.Esqueleto.Internal.Internal

Methods

sqlSelectCols :: IdentInfo -> (a, b, c, d, e) -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy (a, b, c, d, e) -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text (ra, rb, rc, rd, re)

sqlInsertInto :: IdentInfo -> (a, b, c, d, e) -> (Builder, [PersistValue])

(SqlSelect a ra, SqlSelect b rb, SqlSelect c rc, SqlSelect d rd, SqlSelect e re, SqlSelect f rf) => SqlSelect (a, b, c, d, e, f) (ra, rb, rc, rd, re, rf)

Defined in Database.Esqueleto.Internal.Internal

Methods

sqlSelectCols :: IdentInfo -> (a, b, c, d, e, f) -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy (a, b, c, d, e, f) -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text (ra, rb, rc, rd, re, rf)

sqlInsertInto :: IdentInfo -> (a, b, c, d, e, f) -> (Builder, [PersistValue])

(SqlSelect a ra, SqlSelect b rb, SqlSelect c rc, SqlSelect d rd, SqlSelect e re, SqlSelect f rf, SqlSelect g rg) => SqlSelect (a, b, c, d, e, f, g) (ra, rb, rc, rd, re, rf, rg)

Defined in Database.Esqueleto.Internal.Internal

Methods

sqlSelectCols :: IdentInfo -> (a, b, c, d, e, f, g) -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy (a, b, c, d, e, f, g) -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text (ra, rb, rc, rd, re, rf, rg)

sqlInsertInto :: IdentInfo -> (a, b, c, d, e, f, g) -> (Builder, [PersistValue])

(SqlSelect a ra, SqlSelect b rb, SqlSelect c rc, SqlSelect d rd, SqlSelect e re, SqlSelect f rf, SqlSelect g rg, SqlSelect h rh) => SqlSelect (a, b, c, d, e, f, g, h) (ra, rb, rc, rd, re, rf, rg, rh)

Defined in Database.Esqueleto.Internal.Internal

Methods

sqlSelectCols :: IdentInfo -> (a, b, c, d, e, f, g, h) -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy (a, b, c, d, e, f, g, h) -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text (ra, rb, rc, rd, re, rf, rg, rh)

sqlInsertInto :: IdentInfo -> (a, b, c, d, e, f, g, h) -> (Builder, [PersistValue])

(SqlSelect a ra, SqlSelect b rb, SqlSelect c rc, SqlSelect d rd, SqlSelect e re, SqlSelect f rf, SqlSelect g rg, SqlSelect h rh, SqlSelect i ri) => SqlSelect (a, b, c, d, e, f, g, h, i) (ra, rb, rc, rd, re, rf, rg, rh, ri)

Defined in Database.Esqueleto.Internal.Internal

Methods

sqlSelectCols :: IdentInfo -> (a, b, c, d, e, f, g, h, i) -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy (a, b, c, d, e, f, g, h, i) -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text (ra, rb, rc, rd, re, rf, rg, rh, ri)

sqlInsertInto :: IdentInfo -> (a, b, c, d, e, f, g, h, i) -> (Builder, [PersistValue])

(SqlSelect a ra, SqlSelect b rb, SqlSelect c rc, SqlSelect d rd, SqlSelect e re, SqlSelect f rf, SqlSelect g rg, SqlSelect h rh, SqlSelect i ri, SqlSelect j rj) => SqlSelect (a, b, c, d, e, f, g, h, i, j) (ra, rb, rc, rd, re, rf, rg, rh, ri, rj)

Defined in Database.Esqueleto.Internal.Internal

Methods

sqlSelectCols :: IdentInfo -> (a, b, c, d, e, f, g, h, i, j) -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy (a, b, c, d, e, f, g, h, i, j) -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text (ra, rb, rc, rd, re, rf, rg, rh, ri, rj)

sqlInsertInto :: IdentInfo -> (a, b, c, d, e, f, g, h, i, j) -> (Builder, [PersistValue])

(SqlSelect a ra, SqlSelect b rb, SqlSelect c rc, SqlSelect d rd, SqlSelect e re, SqlSelect f rf, SqlSelect g rg, SqlSelect h rh, SqlSelect i ri, SqlSelect j rj, SqlSelect k rk) => SqlSelect (a, b, c, d, e, f, g, h, i, j, k) (ra, rb, rc, rd, re, rf, rg, rh, ri, rj, rk)

Defined in Database.Esqueleto.Internal.Internal

Methods

sqlSelectCols :: IdentInfo -> (a, b, c, d, e, f, g, h, i, j, k) -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy (a, b, c, d, e, f, g, h, i, j, k) -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text (ra, rb, rc, rd, re, rf, rg, rh, ri, rj, rk)

sqlInsertInto :: IdentInfo -> (a, b, c, d, e, f, g, h, i, j, k) -> (Builder, [PersistValue])

(SqlSelect a ra, SqlSelect b rb, SqlSelect c rc, SqlSelect d rd, SqlSelect e re, SqlSelect f rf, SqlSelect g rg, SqlSelect h rh, SqlSelect i ri, SqlSelect j rj, SqlSelect k rk, SqlSelect l rl) => SqlSelect (a, b, c, d, e, f, g, h, i, j, k, l) (ra, rb, rc, rd, re, rf, rg, rh, ri, rj, rk, rl)

Defined in Database.Esqueleto.Internal.Internal

Methods

sqlSelectCols :: IdentInfo -> (a, b, c, d, e, f, g, h, i, j, k, l) -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy (a, b, c, d, e, f, g, h, i, j, k, l) -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text (ra, rb, rc, rd, re, rf, rg, rh, ri, rj, rk, rl)

sqlInsertInto :: IdentInfo -> (a, b, c, d, e, f, g, h, i, j, k, l) -> (Builder, [PersistValue])

(SqlSelect a ra, SqlSelect b rb, SqlSelect c rc, SqlSelect d rd, SqlSelect e re, SqlSelect f rf, SqlSelect g rg, SqlSelect h rh, SqlSelect i ri, SqlSelect j rj, SqlSelect k rk, SqlSelect l rl, SqlSelect m rm) => SqlSelect (a, b, c, d, e, f, g, h, i, j, k, l, m) (ra, rb, rc, rd, re, rf, rg, rh, ri, rj, rk, rl, rm)

Defined in Database.Esqueleto.Internal.Internal

Methods

sqlSelectCols :: IdentInfo -> (a, b, c, d, e, f, g, h, i, j, k, l, m) -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy (a, b, c, d, e, f, g, h, i, j, k, l, m) -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text (ra, rb, rc, rd, re, rf, rg, rh, ri, rj, rk, rl, rm)

sqlInsertInto :: IdentInfo -> (a, b, c, d, e, f, g, h, i, j, k, l, m) -> (Builder, [PersistValue])

(SqlSelect a ra, SqlSelect b rb, SqlSelect c rc, SqlSelect d rd, SqlSelect e re, SqlSelect f rf, SqlSelect g rg, SqlSelect h rh, SqlSelect i ri, SqlSelect j rj, SqlSelect k rk, SqlSelect l rl, SqlSelect m rm, SqlSelect n rn) => SqlSelect (a, b, c, d, e, f, g, h, i, j, k, l, m, n) (ra, rb, rc, rd, re, rf, rg, rh, ri, rj, rk, rl, rm, rn)

Defined in Database.Esqueleto.Internal.Internal

Methods

sqlSelectCols :: IdentInfo -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n) -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy (a, b, c, d, e, f, g, h, i, j, k, l, m, n) -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text (ra, rb, rc, rd, re, rf, rg, rh, ri, rj, rk, rl, rm, rn)

sqlInsertInto :: IdentInfo -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n) -> (Builder, [PersistValue])

(SqlSelect a ra, SqlSelect b rb, SqlSelect c rc, SqlSelect d rd, SqlSelect e re, SqlSelect f rf, SqlSelect g rg, SqlSelect h rh, SqlSelect i ri, SqlSelect j rj, SqlSelect k rk, SqlSelect l rl, SqlSelect m rm, SqlSelect n rn, SqlSelect o ro) => SqlSelect (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) (ra, rb, rc, rd, re, rf, rg, rh, ri, rj, rk, rl, rm, rn, ro)

Defined in Database.Esqueleto.Internal.Internal

Methods

sqlSelectCols :: IdentInfo -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text (ra, rb, rc, rd, re, rf, rg, rh, ri, rj, rk, rl, rm, rn, ro)

sqlInsertInto :: IdentInfo -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) -> (Builder, [PersistValue])

(SqlSelect a ra, SqlSelect b rb, SqlSelect c rc, SqlSelect d rd, SqlSelect e re, SqlSelect f rf, SqlSelect g rg, SqlSelect h rh, SqlSelect i ri, SqlSelect j rj, SqlSelect k rk, SqlSelect l rl, SqlSelect m rm, SqlSelect n rn, SqlSelect o ro, SqlSelect p rp) => SqlSelect (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p) (ra, rb, rc, rd, re, rf, rg, rh, ri, rj, rk, rl, rm, rn, ro, rp)

Defined in Database.Esqueleto.Internal.Internal

Methods

sqlSelectCols :: IdentInfo -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p) -> (Builder, [PersistValue])

sqlSelectColCount :: Proxy (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p) -> Int

sqlSelectProcessRow :: [PersistValue] -> Either Text (ra, rb, rc, rd, re, rf, rg, rh, ri, rj, rk, rl, rm, rn, ro, rp)

sqlInsertInto :: IdentInfo -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p) -> (Builder, [PersistValue])

unescapedColumnNames :: EntityDef -> [DBName]

getEntityVal :: Proxy (SqlExpr (Entity a)) -> Proxy a

materializeExpr :: IdentInfo -> SqlExpr (Value a) -> (Builder, [PersistValue])

Materialize a SqlExpr (Value a).

from3P :: Proxy (a, b, c) -> Proxy ((a, b), c)

from3 :: (a, b, c) -> ((a, b), c)

to3 :: ((a, b), c) -> (a, b, c)

from4P :: Proxy (a, b, c, d) -> Proxy ((a, b), (c, d))

from4 :: (a, b, c, d) -> ((a, b), (c, d))

to4 :: ((a, b), (c, d)) -> (a, b, c, d)

from5P :: Proxy (a, b, c, d, e) -> Proxy ((a, b), (c, d), e)

from5 :: (a, b, c, d, e) -> ((a, b), (c, d), e)

to5 :: ((a, b), (c, d), e) -> (a, b, c, d, e)

from6P :: Proxy (a, b, c, d, e, f) -> Proxy ((a, b), (c, d), (e, f))

from6 :: (a, b, c, d, e, f) -> ((a, b), (c, d), (e, f))

to6 :: ((a, b), (c, d), (e, f)) -> (a, b, c, d, e, f)

from7P :: Proxy (a, b, c, d, e, f, g) -> Proxy ((a, b), (c, d), (e, f), g)

from7 :: (a, b, c, d, e, f, g) -> ((a, b), (c, d), (e, f), g)

to7 :: ((a, b), (c, d), (e, f), g) -> (a, b, c, d, e, f, g)

from8P :: Proxy (a, b, c, d, e, f, g, h) -> Proxy ((a, b), (c, d), (e, f), (g, h))

from8 :: (a, b, c, d, e, f, g, h) -> ((a, b), (c, d), (e, f), (g, h))

to8 :: ((a, b), (c, d), (e, f), (g, h)) -> (a, b, c, d, e, f, g, h)

from9P :: Proxy (a, b, c, d, e, f, g, h, i) -> Proxy ((a, b), (c, d), (e, f), (g, h), i)

from9 :: (a, b, c, d, e, f, g, h, i) -> ((a, b), (c, d), (e, f), (g, h), i)

to9 :: ((a, b), (c, d), (e, f), (g, h), i) -> (a, b, c, d, e, f, g, h, i)

from10P :: Proxy (a, b, c, d, e, f, g, h, i, j) -> Proxy ((a, b), (c, d), (e, f), (g, h), (i, j))

from10 :: (a, b, c, d, e, f, g, h, i, j) -> ((a, b), (c, d), (e, f), (g, h), (i, j))

to10 :: ((a, b), (c, d), (e, f), (g, h), (i, j)) -> (a, b, c, d, e, f, g, h, i, j)

from11P :: Proxy (a, b, c, d, e, f, g, h, i, j, k) -> Proxy ((a, b), (c, d), (e, f), (g, h), (i, j), k)

to11 :: ((a, b), (c, d), (e, f), (g, h), (i, j), k) -> (a, b, c, d, e, f, g, h, i, j, k)

from12P :: Proxy (a, b, c, d, e, f, g, h, i, j, k, l) -> Proxy ((a, b), (c, d), (e, f), (g, h), (i, j), (k, l))

to12 :: ((a, b), (c, d), (e, f), (g, h), (i, j), (k, l)) -> (a, b, c, d, e, f, g, h, i, j, k, l)

from13P :: Proxy (a, b, c, d, e, f, g, h, i, j, k, l, m) -> Proxy ((a, b), (c, d), (e, f), (g, h), (i, j), (k, l), m)

to13 :: ((a, b), (c, d), (e, f), (g, h), (i, j), (k, l), m) -> (a, b, c, d, e, f, g, h, i, j, k, l, m)

from14P :: Proxy (a, b, c, d, e, f, g, h, i, j, k, l, m, n) -> Proxy ((a, b), (c, d), (e, f), (g, h), (i, j), (k, l), (m, n))

to14 :: ((a, b), (c, d), (e, f), (g, h), (i, j), (k, l), (m, n)) -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n)

from15P :: Proxy (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) -> Proxy ((a, b), (c, d), (e, f), (g, h), (i, j), (k, l), (m, n), o)

to15 :: ((a, b), (c, d), (e, f), (g, h), (i, j), (k, l), (m, n), o) -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o)

from16P :: Proxy (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p) -> Proxy ((a, b), (c, d), (e, f), (g, h), (i, j), (k, l), (m, n), (o, p))

to16 :: ((a, b), (c, d), (e, f), (g, h), (i, j), (k, l), (m, n), (o, p)) -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p)

insertSelect :: (MonadIO m, PersistEntity a, SqlBackendCanWrite backend) => SqlQuery (SqlExpr (Insertion a)) -> ReaderT backend m ()

Insert a PersistField for every selected value.

Since: 2.4.2

insertSelectCount :: (MonadIO m, PersistEntity a, SqlBackendCanWrite backend) => SqlQuery (SqlExpr (Insertion a)) -> ReaderT backend m Int64

Insert a PersistField for every selected value, return the count afterward

renderExpr :: SqlBackend -> SqlExpr (Value Bool) -> Text

Renders an expression into Text. Only useful for creating a textual representation of the clauses passed to an On clause.

Since: 3.2.0

data RenderExprException

An exception thrown by RenderExpr - it's not designed to handle composite keys, and will blow up if you give it one.

Since: 3.2.0

Constructors

RenderExprUnexpectedECompositeKey Text

Instances

Exception RenderExprException

Since: 3.2.0

Defined in Database.Esqueleto.Internal.Internal

Methods

toException :: RenderExprException -> SomeException

fromException :: SomeException -> Maybe RenderExprException

displayException :: RenderExprException -> String

Show RenderExprException

Defined in Database.Esqueleto.Internal.Internal

Methods

showsPrec :: Int -> RenderExprException -> ShowS

show :: RenderExprException -> String

showList :: [RenderExprException] -> ShowS

valkey :: (ToBackendKey SqlBackend entity, PersistField (Key entity)) => Int64 -> SqlExpr (Value (Key entity))

valkey i = val . toSqlKey (https://github.com/prowdsponsor/esqueleto/issues/9).

valJ :: PersistField (Key entity) => Value (Key entity) -> SqlExpr (Value (Key entity))

valJ is like val but for something that is already a Value. The use case it was written for was, given a Value lift the Key for that Value into the query expression in a type safe way. However, the implementation is more generic than that so we call it valJ.

Its important to note that the input entity and the output entity are constrained to be the same by the type signature on the function (https://github.com/prowdsponsor/esqueleto/pull/69).

Since: 1.4.2

deleteKey :: (PersistStore backend, BaseBackend backend ~ PersistEntityBackend val, MonadIO m, PersistEntity val) => Key val -> ReaderT backend m ()

Synonym for delete that does not clash with esqueleto's delete.

associateJoin :: forall e1 e0. Ord (Key e0) => [(Entity e0, e1)] -> Map (Key e0) (e0, [e1])

Avoid N+1 queries and join entities into a map structure.

This function is useful to call on the result of a single JOIN. For example, suppose you have this query:

getFoosAndNestedBarsFromParent
    :: ParentId
    -> SqlPersistT IO [(Entity Foo, Maybe (Entity Bar))]
getFoosAndNestedBarsFromParent parentId =
    select $ do
        (foo :& bar) <- from $
            table Foo
            `LeftOuterJoin`
            table Bar
                `on` do
                    \(foo :& bar) ->
                        foo ^. FooId ==. bar ?. BarFooId
        where_ $
            foo ^. FooParentId ==. val parentId
        pure (foo, bar)

This is a natural result type for SQL - a list of tuples. However, it's not what we usually want in Haskell - each Foo in the list will be represented multiple times, once for each Bar.

We can write fmap associateJoin and it will translate it into a Map that is keyed on the Key of the left Entity, and the value is a tuple of the entity's value as well as the list of each coresponding entity.

getFoosAndNestedBarsFromParentHaskellese
    :: ParentId
    -> SqlPersistT (Map (Key Foo) (Foo, [Maybe (Entity Bar)]))
getFoosAndNestedBarsFromParentHaskellese parentId =
    fmap associateJoin $ getFoosdAndNestedBarsFromParent parentId

What if you have multiple joins?

Let's use associateJoin with a *two* join query.

userPostComments
    :: SqlQuery (SqlExpr (Entity User, Entity Post, Entity Comment))
userPostsComment = do
    (u :& p :& c) <- from $
        table User
        `InnerJoin`
        table Post
            on do
                \(u :& p) ->
                    u ^. UserId ==. p ^. PostUserId
        `InnerJoin`
        table @Comment
            `on` do
                \(_ :& p :& c) ->
                    p ^. PostId ==. c ^. CommentPostId
    pure (u, p, c)

This query returns a User, with all of the users Posts, and then all of the Comments on that post.

First, we *nest* the tuple.

nest :: (a, b, c) -> (a, (b, c))
nest (a, b, c) = (a, (b, c))

This makes the return of the query conform to the input expected from associateJoin.

nestedUserPostComments
    :: SqlPersistT IO [(Entity User, (Entity Post, Entity Comment))]
nestedUserPostComments =
    fmap nest $ select userPostsComments

Now, we can call associateJoin on it.

associateUsers
    :: [(Entity User, (Entity Post, Entity Comment))]
    -> Map UserId (User, [(Entity Post, Entity Comment)])
associateUsers =
    associateJoin

Next, we'll use the Functor instances for Map and tuple to call associateJoin on the [(Entity Post, Entity Comment)].

associatePostsAndComments
    :: Map UserId (User, [(Entity Post, Entity Comment)])
    -> Map UserId (User, Map PostId (Post, [Entity Comment]))
associatePostsAndComments =
    fmap (fmap associateJoin)

For more reading on this topic, see this Foxhound Systems blog post.

Since: 3.1.2