Safe Haskell | None |
---|---|

Language | Haskell98 |

The `esqueleto`

EDSL (embedded domain specific language).
This module replaces `Database.Persist`

, so instead of
importing that module you should just import this one:

-- For a module using just esqueleto. import Database.Esqueleto

If you need to use `persistent`

's default support for queries
as well, either import it qualified:

-- For a module that mostly uses esqueleto. import Database.Esqueleto import qualified Database.Persistent as P

or import `esqueleto`

itself qualified:

-- For a module uses esqueleto just on some queries. import Database.Persistent import qualified Database.Esqueleto as E

Other than identifier name clashes, `esqueleto`

does not
conflict with `persistent`

in any way.

- class (Functor query, Applicative query, Monad query) => Esqueleto query expr backend | query -> expr backend, expr -> query backend where
- where_ :: expr (Value Bool) -> query ()
- on :: expr (Value Bool) -> query ()
- groupBy :: ToSomeValues expr a => a -> query ()
- orderBy :: [expr OrderBy] -> query ()
- asc :: PersistField a => expr (Value a) -> expr OrderBy
- desc :: PersistField a => expr (Value a) -> expr OrderBy
- limit :: Int64 -> query ()
- offset :: Int64 -> query ()
- rand :: expr OrderBy
- having :: expr (Value Bool) -> query ()
- sub_select :: PersistField a => query (expr (Value a)) -> expr (Value a)
- sub_selectDistinct :: PersistField a => query (expr (Value a)) -> expr (Value a)
- (^.) :: (PersistEntity val, PersistField typ) => expr (Entity val) -> EntityField val typ -> expr (Value typ)
- (?.) :: (PersistEntity val, PersistField typ) => expr (Maybe (Entity val)) -> EntityField val typ -> expr (Value (Maybe typ))
- val :: PersistField typ => typ -> expr (Value typ)
- isNothing :: PersistField typ => expr (Value (Maybe typ)) -> expr (Value Bool)
- just :: expr (Value typ) -> expr (Value (Maybe typ))
- nothing :: expr (Value (Maybe typ))
- joinV :: expr (Value (Maybe (Maybe typ))) -> expr (Value (Maybe typ))
- countRows :: Num a => expr (Value a)
- count :: Num a => expr (Value typ) -> expr (Value a)
- not_ :: expr (Value Bool) -> expr (Value Bool)
- (==.) :: PersistField typ => expr (Value typ) -> expr (Value typ) -> expr (Value Bool)
- (>=.) :: PersistField typ => expr (Value typ) -> expr (Value typ) -> expr (Value Bool)
- (>.) :: PersistField typ => expr (Value typ) -> expr (Value typ) -> expr (Value Bool)
- (<=.) :: PersistField typ => expr (Value typ) -> expr (Value typ) -> expr (Value Bool)
- (<.) :: PersistField typ => expr (Value typ) -> expr (Value typ) -> expr (Value Bool)
- (!=.) :: PersistField typ => expr (Value typ) -> expr (Value typ) -> expr (Value Bool)
- (&&.) :: expr (Value Bool) -> expr (Value Bool) -> expr (Value Bool)
- (||.) :: expr (Value Bool) -> expr (Value Bool) -> expr (Value Bool)
- (+.) :: PersistField a => expr (Value a) -> expr (Value a) -> expr (Value a)
- (-.) :: PersistField a => expr (Value a) -> expr (Value a) -> expr (Value a)
- (/.) :: PersistField a => expr (Value a) -> expr (Value a) -> expr (Value a)
- (*.) :: PersistField a => expr (Value a) -> expr (Value a) -> expr (Value a)
- random_ :: (PersistField a, Num a) => expr (Value a)
- round_ :: (PersistField a, Num a, PersistField b, Num b) => expr (Value a) -> expr (Value b)
- ceiling_ :: (PersistField a, Num a, PersistField b, Num b) => expr (Value a) -> expr (Value b)
- floor_ :: (PersistField a, Num a, PersistField b, Num b) => expr (Value a) -> expr (Value b)
- sum_ :: (PersistField a, PersistField b) => expr (Value a) -> expr (Value (Maybe b))
- min_ :: PersistField a => expr (Value a) -> expr (Value (Maybe a))
- max_ :: PersistField a => expr (Value a) -> expr (Value (Maybe a))
- avg_ :: (PersistField a, PersistField b) => expr (Value a) -> expr (Value (Maybe b))
- coalesce :: PersistField a => [expr (Value (Maybe a))] -> expr (Value (Maybe a))
- coalesceDefault :: PersistField a => [expr (Value (Maybe a))] -> expr (Value a) -> expr (Value a)
- like :: (PersistField s, IsString s) => expr (Value s) -> expr (Value s) -> expr (Value Bool)
- (%) :: (PersistField s, IsString s) => expr (Value s)
- concat_ :: (PersistField s, IsString s) => [expr (Value s)] -> expr (Value s)
- (++.) :: (PersistField s, IsString s) => expr (Value s) -> expr (Value s) -> expr (Value s)
- subList_select :: PersistField a => query (expr (Value a)) -> expr (ValueList a)
- subList_selectDistinct :: PersistField a => query (expr (Value a)) -> expr (ValueList a)
- valList :: PersistField typ => [typ] -> expr (ValueList typ)
- in_ :: PersistField typ => expr (Value typ) -> expr (ValueList typ) -> expr (Value Bool)
- notIn :: PersistField typ => expr (Value typ) -> expr (ValueList typ) -> expr (Value Bool)
- exists :: query () -> expr (Value Bool)
- notExists :: query () -> expr (Value Bool)
- set :: PersistEntity val => expr (Entity val) -> [expr (Update val)] -> query ()
- (=.) :: (PersistEntity val, PersistField typ) => EntityField val typ -> expr (Value typ) -> expr (Update val)
- (+=.) :: (PersistEntity val, PersistField a) => EntityField val a -> expr (Value a) -> expr (Update val)
- (-=.) :: (PersistEntity val, PersistField a) => EntityField val a -> expr (Value a) -> expr (Update val)
- (*=.) :: (PersistEntity val, PersistField a) => EntityField val a -> expr (Value a) -> expr (Update val)
- (/=.) :: (PersistEntity val, PersistField a) => EntityField val a -> expr (Value a) -> expr (Update val)
- (<#) :: (a -> b) -> expr (Value a) -> expr (Insertion b)
- (<&>) :: expr (Insertion (a -> b)) -> expr (Value a) -> expr (Insertion b)
- case_ :: PersistField a => [(expr (Value Bool), expr (Value a))] -> expr (Value a) -> expr (Value a)

- when_ :: expr (Value Bool) -> () -> expr a -> (expr (Value Bool), expr a)
- then_ :: ()
- else_ :: expr a -> expr a
- from :: From query expr backend a => (a -> query b) -> query b
- data Value a = Value a
- unValue :: Value a -> a
- data ValueList a = ValueList a
- data OrderBy
- data InnerJoin a b = a `InnerJoin` b
- data CrossJoin a b = a `CrossJoin` b
- data LeftOuterJoin a b = a `LeftOuterJoin` b
- data RightOuterJoin a b = a `RightOuterJoin` b
- data FullOuterJoin a b = a `FullOuterJoin` b
- data OnClauseWithoutMatchingJoinException = OnClauseWithoutMatchingJoinException String
- data SqlQuery a
- data SqlExpr a
- type SqlEntity ent = (PersistEntity ent, PersistEntityBackend ent ~ SqlBackend)
- select :: (SqlSelect a r, MonadIO m) => SqlQuery a -> SqlPersistT m [r]
- selectDistinct :: (SqlSelect a r, MonadIO m) => SqlQuery a -> SqlPersistT m [r]
- selectSource :: (SqlSelect a r, MonadResource m) => SqlQuery a -> Source (SqlPersistT m) r
- selectDistinctSource :: (SqlSelect a r, MonadResource m) => SqlQuery a -> Source (SqlPersistT m) r
- delete :: MonadIO m => SqlQuery () -> SqlPersistT m ()
- deleteCount :: MonadIO m => SqlQuery () -> SqlPersistT m Int64
- update :: (MonadIO m, SqlEntity val) => (SqlExpr (Entity val) -> SqlQuery ()) -> SqlPersistT m ()
- updateCount :: (MonadIO m, SqlEntity val) => (SqlExpr (Entity val) -> SqlQuery ()) -> SqlPersistT m Int64
- insertSelect :: (MonadIO m, PersistEntity a) => SqlQuery (SqlExpr (Insertion a)) -> SqlPersistT m ()
- insertSelectDistinct :: (MonadIO m, PersistEntity a) => SqlQuery (SqlExpr (Insertion a)) -> SqlPersistT m ()
- valkey :: (Esqueleto query expr backend, ToBackendKey SqlBackend entity, PersistField (Key entity)) => Int64 -> expr (Value (Key entity))
- valJ :: (Esqueleto query expr backend, PersistField (Key entity)) => Value (Key entity) -> expr (Value (Key entity))
- deleteKey :: (PersistStore (PersistEntityBackend val), MonadIO m, PersistEntity val) => Key val -> ReaderT (PersistEntityBackend val) m ()
- module Database.Persist.Sql

# Setup

If you're already using `persistent`

, then you're ready to use
`esqueleto`

, no further setup is needed. If you're just
starting a new project and would like to use `esqueleto`

, take
a look at `persistent`

's book first
(http://www.yesodweb.com/book/persistent) to learn how to
define your schema.

# Introduction

The main goals of `esqueleto`

are to:

- Be easily translatable to SQL. When you take a look at a
`esqueleto`

query, you should be able to know exactly how the SQL query will end up. (As opposed to being a relational algebra EDSL such as HaskellDB, which is non-trivial to translate into SQL.) - Support the mostly used SQL features. We'd like you to be
able to use
`esqueleto`

for all of your queries, no exceptions. Send a pull request or open an issue on our project page (https://github.com/meteficha/esqueleto) if there's anything missing that you'd like to see. - Be as type-safe as possible. We strive to provide as many type checks as possible. If you get bitten by some invalid code that type-checks, please open an issue on our project page so we can take a look.

However, it is *not* a goal to be able to write portable SQL.
We do not try to hide the differences between DBMSs from you,
and `esqueleto`

code that works for one database may not work
on another. This is a compromise we have to make in order to
give you as much control over the raw SQL as possible without
losing too much convenience. This also means that you may
type-check a query that doesn't work on your DBMS.

# Getting started

We like clean, easy-to-read EDSLs. However, in order to achieve this goal we've used a lot of type hackery, leading to some hard-to-read type signatures. On this section, we'll try to build some intuition about the syntax.

For the following examples, we'll use this example schema:

share [mkPersist sqlSettings, mkMigrate "migrateAll"] [persist| Person name String age Int Maybe deriving Eq Show BlogPost title String authorId PersonId deriving Eq Show Follow follower PersonId followed PersonId deriving Eq Show |]

Most of `esqueleto`

was created with `SELECT`

statements in
mind, not only because they're the most common but also
because they're the most complex kind of statement. The most
simple kind of `SELECT`

would be:

SELECT * FROM Person

In `esqueleto`

, we may write the same query above as:

do people <-`select`

$`from`

$ \person -> do return person liftIO $ mapM_ (putStrLn . personName . entityVal) people

The expression above has type `SqlPersist m ()`

, while
`people`

has type `[Entity Person]`

. The query above will be
translated into exactly the same query we wrote manually, but
instead of `SELECT *`

it will list all entity fields (using
`*`

is not robust). Note that `esqueleto`

knows that we want
an `Entity Person`

just because of the `personName`

that we're
printing later.

However, most of the time we need to filter our queries using
`WHERE`

. For example:

SELECT * FROM Person WHERE Person.name = "John"

In `esqueleto`

, we may write the same query above as:

select $ from $ \p -> do`where_`

(p`^.`

PersonName`==.`

`val`

"John") return p

Although `esqueleto`

's code is a bit more noisy, it's has
almost the same structure (save from the `return`

). The
`(`

operator is used to project a field from an entity.
The field name is the same one generated by `^.`

)`persistent`

's
Template Haskell functions. We use `val`

to lift a constant
Haskell value into the SQL query.

Another example would be:

SELECT * FROM Person WHERE Person.age >= 18

In `esqueleto`

, we may write the same query above as:

select $ from $ \p -> do where_ (p ^. PersonAge`>=.`

`just`

(val 18)) return p

Since `age`

is an optional `Person`

field, we use `just`

lift
`val 18 :: SqlExpr (Value Int)`

into ```
just (val 18) ::
SqlExpr (Value (Maybe Int))
```

.

Implicit joins are represented by tuples. For example, to get the list of all blog posts and their authors, we could write:

SELECT BlogPost.*, Person.* FROM BlogPost, Person WHERE BlogPost.authorId = Person.id ORDER BY BlogPost.title ASC

In `esqueleto`

, we may write the same query above as:

select $ from $ \(b, p) -> do where_ (b ^. BlogPostAuthorId ==. p ^. PersonId)`orderBy`

[`asc`

(b ^. BlogPostTitle)] return (b, p)

However, we may want your results to include people who don't
have any blog posts as well using a `LEFT OUTER JOIN`

:

SELECT Person.*, BlogPost.* FROM Person LEFT OUTER JOIN BlogPost ON Person.id = BlogPost.authorId ORDER BY Person.name ASC, BlogPost.title ASC

In `esqueleto`

, we may write the same query above as:

select $ from $ \(p ``LeftOuterJoin`` mb) -> do`on`

(just (p ^. PersonId) ==. mb`?.`

BlogPostAuthorId) orderBy [asc (p ^. PersonName), asc (mb`?.`

BlogPostTitle)] return (p, mb)

On a `LEFT OUTER JOIN`

the entity on the right hand side may
not exist (i.e. there may be a `Person`

without any
`BlogPost`

s), so while `p :: SqlExpr (Entity Person)`

, we have
`mb :: SqlExpr (Maybe (Entity BlogPost))`

. The whole
expression above has type ```
SqlPersist m [(Entity Person, Maybe
(Entity BlogPost))]
```

. Instead of using `(^.)`

, we used
`(`

to project a field from a `?.`

)`Maybe (Entity a)`

.

We are by no means limited to joins of two tables, nor by
joins of different tables. For example, we may want a list
the `Follow`

entity:

SELECT P1.*, Follow.*, P2.* FROM Person AS P1 INNER JOIN Follow ON P1.id = Follow.follower INNER JOIN P2 ON P2.id = Follow.followed

In `esqueleto`

, we may write the same query above as:

select $ from $ \(p1 ``InnerJoin`` f ``InnerJoin`` p2) -> do on (p2 ^. PersonId ==. f ^. FollowFollowed) on (p1 ^. PersonId ==. f ^. FollowFollower) return (p1, f, p2)

*Note carefully that the order of the ON clauses is*
*reversed!* You're required to write your `on`

s in reverse
order because that helps composability (see the documentation
of `on`

for more details).

We also currently support `UPDATE`

and `DELETE`

statements.
For example:

do`update`

$ \p -> do`set`

p [ PersonName`=.`

val "João" ] where_ (p ^. PersonName ==. val "Joao")`delete`

$ from $ \p -> do where_ (p ^. PersonAge <. just (val 14))

The results of queries can also be used for insertions.
In `SQL`

, we might write the following, inserting a new blog
post for every user:

INSERT INTO BlogPost SELECT ('Group Blog Post', id) FROM Person

In `esqueleto`

, we may write the same query above as:

insertSelect $ from $ \p-> return $ BlogPost <# "Group Blog Post" <&> (p ^. PersonId)

Individual insertions can be performed through Persistent's
`insert`

function, reexported for convenience.

`esqueleto`

's Language

class (Functor query, Applicative query, Monad query) => Esqueleto query expr backend | query -> expr backend, expr -> query backend where Source

Finally tagless representation of `esqueleto`

's EDSL.

fromStart, fromStartMaybe, fromJoin, fromFinish, where_, on, groupBy, orderBy, asc, desc, limit, offset, rand, having, sub_select, sub_selectDistinct, (^.), (?.), val, isNothing, just, nothing, joinV, countRows, count, not_, (==.), (>=.), (>.), (<=.), (<.), (!=.), (&&.), (||.), (+.), (-.), (/.), (*.), random_, round_, ceiling_, floor_, sum_, min_, max_, avg_, coalesce, coalesceDefault, like, (%), concat_, (++.), subList_select, subList_selectDistinct, valList, in_, notIn, exists, notExists, set, (=.), (+=.), (-=.), (*=.), (/=.), (<#), (<&>), case_

where_ :: expr (Value Bool) -> query () Source

`WHERE`

clause: restrict the query's result.

on :: expr (Value Bool) -> query () Source

`ON`

clause: restrict the a `JOIN`

's result. The `ON`

clause will be applied to the *last* `JOIN`

that does not
have an `ON`

clause yet. If there are no `JOIN`

s without
`ON`

clauses (either because you didn't do any `JOIN`

, or
because all `JOIN`

s already have their own `ON`

clauses), a
runtime exception `OnClauseWithoutMatchingJoinException`

is
thrown. `ON`

clauses are optional when doing `JOIN`

s.

On the simple case of doing just one `JOIN`

, for example

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

there's no ambiguity and the rules above just mean that
you're allowed to call `on`

only once (as in SQL). If you
have many joins, then the `on`

s are applied on the *reverse*
order that the `JOIN`

s appear. For example:

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

The order is *reversed* in order to improve composability.
For example, consider `query1`

and `query2`

below:

let query1 = from $ \(foo ``InnerJoin`` bar) -> do on (foo ^. FooId ==. bar ^. BarFooId) query2 = from $ \(mbaz ``LeftOuterJoin`` quux) -> do return (mbaz ?. BazName, quux) test1 = (,) <$> query1 <*> query2 test2 = flip (,) <$> query2 <*> query1

If the order was *not* reversed, then `test2`

would be
broken: `query1`

's `on`

would refer to `query2`

's
`LeftOuterJoin`

.

groupBy :: ToSomeValues expr a => a -> query () Source

`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
`SqlExpr (Value Int)`

to avoid ambiguity):

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)

orderBy :: [expr OrderBy] -> query () Source

asc :: PersistField a => expr (Value a) -> expr OrderBy Source

Ascending order of this field or expression.

desc :: PersistField a => expr (Value a) -> expr OrderBy Source

Descending order of this field or expression.

limit :: Int64 -> query () Source

`LIMIT`

. Limit the number of returned rows.

offset :: Int64 -> query () Source

`OFFSET`

. Usually used with `limit`

.

`ORDER BY random()`

clause.

*Since: 1.3.10*

having :: expr (Value Bool) -> query () Source

`HAVING`

.

*Since: 1.2.2*

sub_select :: PersistField a => query (expr (Value a)) -> expr (Value a) Source

Execute a subquery `SELECT`

in an expression. Returns a
simple value so should be used only when the `SELECT`

query
is guaranteed to return just one row.

sub_selectDistinct :: PersistField a => query (expr (Value a)) -> expr (Value a) Source

Same as `sub_select`

but using `SELECT DISTINCT`

.

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

Project a field of an entity.

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

Project a field of an entity that may be null.

val :: PersistField typ => typ -> expr (Value typ) Source

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

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

`IS NULL`

comparison.

just :: expr (Value typ) -> expr (Value (Maybe typ)) Source

Analogous to `Just`

, promotes a value of type `typ`

into
one of type `Maybe typ`

. It should hold that ```
val . Just
=== just . val
```

.

nothing :: expr (Value (Maybe typ)) Source

`NULL`

value.

joinV :: expr (Value (Maybe (Maybe typ))) -> expr (Value (Maybe typ)) Source

Join nested `Maybe`

s in a `Value`

into one. This is useful when
calling aggregate functions on nullable fields.

countRows :: Num a => expr (Value a) Source

`COUNT(*)`

value.

count :: Num a => expr (Value typ) -> expr (Value a) Source

`COUNT`

.

not_ :: expr (Value Bool) -> expr (Value Bool) Source

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

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

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

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

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

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

(&&.) :: expr (Value Bool) -> expr (Value Bool) -> expr (Value Bool) infixr 3 Source

(||.) :: expr (Value Bool) -> expr (Value Bool) -> expr (Value Bool) infixr 2 Source

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

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

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

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

random_ :: (PersistField a, Num a) => expr (Value a) Source

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

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

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

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

min_ :: PersistField a => expr (Value a) -> expr (Value (Maybe a)) Source

max_ :: PersistField a => expr (Value a) -> expr (Value (Maybe a)) Source

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

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

`COALESCE`

function. Evaluates the arguments in order and
returns the value of the first non-NULL expression, 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 => [expr (Value (Maybe a))] -> expr (Value a) -> expr (Value a) Source

Like `coalesce`

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

*Since: 1.4.3*

like :: (PersistField s, IsString s) => expr (Value s) -> expr (Value s) -> expr (Value Bool) infixr 2 Source

`LIKE`

operator.

(%) :: (PersistField s, IsString s) => expr (Value s) Source

The string

. May be useful while using `%`

`like`

and
concatenation (`concat_`

or `++.`

, depending on your
database). Note that you always to type the parenthesis,
for example:

`name ````like'`

` (%) ++. val John ++. (%)

concat_ :: (PersistField s, IsString s) => [expr (Value s)] -> expr (Value s) Source

The `CONCAT`

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

(++.) :: (PersistField s, IsString s) => expr (Value s) -> expr (Value s) -> expr (Value s) infixr 5 Source

The `||`

string concatenation operator (named after
Haskell's `++`

in order to avoid naming clash with `||.`

).
Supported by SQLite and PostgreSQL.

subList_select :: PersistField a => query (expr (Value a)) -> expr (ValueList a) Source

Execute a subquery `SELECT`

in an expression. Returns a
list of values.

subList_selectDistinct :: PersistField a => query (expr (Value a)) -> expr (ValueList a) Source

Same as `sublist_select`

but using `SELECT DISTINCT`

.

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

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

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

`IN`

operator.

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

`NOT IN`

operator.

exists :: query () -> expr (Value Bool) Source

`EXISTS`

operator. For example:

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

notExists :: query () -> expr (Value Bool) Source

`NOT EXISTS`

operator.

set :: PersistEntity val => expr (Entity val) -> [expr (Update val)] -> query () Source

`SET`

clause used on `UPDATE`

s. 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 -> expr (Value typ) -> expr (Update val) infixr 3 Source

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

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

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

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

(<#) :: (a -> b) -> expr (Value a) -> expr (Insertion b) Source

Apply a `PersistField`

constructor to `expr Value`

arguments.

(<&>) :: expr (Insertion (a -> b)) -> expr (Value a) -> expr (Insertion b) Source

Apply extra `expr Value`

arguments to a `PersistField`

constructor

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

`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*

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

Syntax sugar for `case_`

.

*Since: 2.1.2*

from :: From query expr backend a => (a -> query b) -> query b Source

`FROM`

clause: bring entities into scope.

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 JOIN`

s.- 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 right fixity, the same as in SQL.

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 (expr (Entity Person)) (InnerJoin (expr (Entity Follow)) (expr (Entity Person))) ((p1 ``InnerJoin`` f) ``InnerJoin`` p2) :: :: (...) => InnerJoin (InnerJoin (expr (Entity Person)) (expr (Entity Follow))) (expr (Entity Person))

Note that some backends may not support all kinds of `JOIN`

s.
For example, when using the SQL backend with SQLite, it will
not accept the last example above (which is associated to the
left, instead of being to the right) and will not accept
`RightOuterJoin`

s or `FullOuterJoin`

s.

A single value (as opposed to a whole entity). You may use
`(`

or `^.`

)`(`

to get a `?.`

)`Value`

from an `Entity`

.

Value 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`

).

## Joins

data InnerJoin a b infixr 2 Source

Data type that represents an `INNER JOIN`

(see `LeftOuterJoin`

for an example).

a `InnerJoin` b infixr 2 |

IsJoinKind InnerJoin | |

(Esqueleto query expr backend, FromPreprocess query expr backend (InnerJoin a b)) => From query expr backend (InnerJoin a b) |

data CrossJoin a b infixr 2 Source

Data type that represents a `CROSS JOIN`

(see `LeftOuterJoin`

for an example).

a `CrossJoin` b infixr 2 |

IsJoinKind CrossJoin | |

(Esqueleto query expr backend, FromPreprocess query expr backend (CrossJoin a b)) => From query expr backend (CrossJoin a b) |

data LeftOuterJoin a b infixr 2 Source

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`

.

a `LeftOuterJoin` b infixr 2 |

IsJoinKind LeftOuterJoin | |

(Esqueleto query expr backend, FromPreprocess query expr backend (LeftOuterJoin a b)) => From query expr backend (LeftOuterJoin a b) |

data RightOuterJoin a b infixr 2 Source

Data type that represents a `RIGHT OUTER JOIN`

(see `LeftOuterJoin`

for an example).

a `RightOuterJoin` b infixr 2 |

IsJoinKind RightOuterJoin | |

(Esqueleto query expr backend, FromPreprocess query expr backend (RightOuterJoin a b)) => From query expr backend (RightOuterJoin a b) |

data FullOuterJoin a b infixr 2 Source

Data type that represents a `FULL OUTER JOIN`

(see `LeftOuterJoin`

for an example).

a `FullOuterJoin` b infixr 2 |

IsJoinKind FullOuterJoin | |

(Esqueleto query expr backend, FromPreprocess query expr backend (FullOuterJoin a b)) => From query expr backend (FullOuterJoin a b) |

data OnClauseWithoutMatchingJoinException Source

Exception thrown whenever `on`

is used to create an `ON`

clause but no matching `JOIN`

is found.

# SQL backend

SQL backend for `esqueleto`

using `SqlPersistT`

.

An expression on the SQL backend.

Esqueleto SqlQuery SqlExpr SqlBackend | |

ToSomeValues SqlExpr (SqlExpr (Value a)) | |

(~) * a (Value b) => UnsafeSqlFunctionArgument (SqlExpr a) | |

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

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

PersistField a => SqlSelect (SqlExpr (Value a)) (Value a) | You may return any single value (i.e. a single column) from
a |

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

Constraint synonym for `persistent`

entities whose backend
is `SqlPersistT`

.

select :: (SqlSelect a r, MonadIO m) => SqlQuery a -> SqlPersistT m [r] Source

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 (`

for an entity`Entity`

v)`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 JOIN`

s. - You may return a
`SqlExpr (`

for a value`Value`

t)`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`sub_select`

).

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)`

.

selectDistinct :: (SqlSelect a r, MonadIO m) => SqlQuery a -> SqlPersistT m [r] Source

Execute an `esqueleto`

`SELECT DISTINCT`

query inside
`persistent`

's `SqlPersistT`

monad and return a list of rows.

selectSource :: (SqlSelect a r, MonadResource m) => SqlQuery a -> Source (SqlPersistT m) r Source

Execute an `esqueleto`

`SELECT`

query inside `persistent`

's
`SqlPersistT`

monad and return a `Source`

of rows.

selectDistinctSource :: (SqlSelect a r, MonadResource m) => SqlQuery a -> Source (SqlPersistT m) r Source

Execute an `esqueleto`

`SELECT DISTINCT`

query inside
`persistent`

's `SqlPersistT`

monad and return a `Source`

of
rows.

delete :: MonadIO m => SqlQuery () -> SqlPersistT m () Source

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 ()

deleteCount :: MonadIO m => SqlQuery () -> SqlPersistT m Int64 Source

Same as `delete`

, but returns the number of rows affected.

update :: (MonadIO m, SqlEntity val) => (SqlExpr (Entity val) -> SqlQuery ()) -> SqlPersistT m () Source

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, SqlEntity val) => (SqlExpr (Entity val) -> SqlQuery ()) -> SqlPersistT m Int64 Source

Same as `update`

, but returns the number of rows affected.

insertSelect :: (MonadIO m, PersistEntity a) => SqlQuery (SqlExpr (Insertion a)) -> SqlPersistT m () Source

Insert a `PersistField`

for every selected value.

insertSelectDistinct :: (MonadIO m, PersistEntity a) => SqlQuery (SqlExpr (Insertion a)) -> SqlPersistT m () Source

Insert a `PersistField`

for every unique selected value.

# Helpers

valkey :: (Esqueleto query expr backend, ToBackendKey SqlBackend entity, PersistField (Key entity)) => Int64 -> expr (Value (Key entity)) Source

`valkey i = val (Key (PersistInt64 i))`

(https://github.com/meteficha/esqueleto/issues/9).

valJ :: (Esqueleto query expr backend, PersistField (Key entity)) => Value (Key entity) -> expr (Value (Key entity)) Source

`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*

# Re-exports

We re-export many symbols from `persistent`

for convenince:

- "Store functions" from Database.Persist.
- Everything from Database.Persist.Class except for
`PersistQuery`

and`delete`

(use`deleteKey`

instead). - Everything from Database.Persist.Types except for
`Update`

,`SelectOpt`

,`BackendSpecificFilter`

and`Filter`

. - Everything from Database.Persist.Sql except for
`deleteWhereCount`

and`updateWhereCount`

.

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

module Database.Persist.Sql