Database.Esqueleto.Internal.Language

Documentation

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

Finally tagless representation of esqueleto's EDSL.

Methods

fromStart :: (PersistEntity a, PersistEntityBackend a ~ backend) => query (expr (PreprocessedFrom (expr (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.

fromStartMaybe :: (PersistEntity a, PersistEntityBackend a ~ backend) => query (expr (PreprocessedFrom (expr (Maybe (Entity a)))))

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

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

(Internal) Do a JOIN.

fromFinish :: expr (PreprocessedFrom a) -> query a

(Internal) Finish a JOIN.

where_ :: expr (Single Bool) -> query ()

WHERE clause: restrict the query's result.

on :: expr (Single Bool) -> query ()

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 JOINs without ON clauses (either because you didn't do any JOIN, or because all JOINs already have their own ON clauses), a runtime exception OnClauseWithoutMatchingJoinException is thrown. ON clauses are optional when doing JOINs.

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 ons are applied on the reverse order that the JOINs 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.

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

ORDER BY clause. See also asc and desc.

asc :: PersistField a => expr (Single a) -> expr OrderBy

Ascending order of this field or expression.

desc :: PersistField a => expr (Single a) -> expr OrderBy

Descending order of this field or expression.

sub_select :: PersistField a => query (expr (Single a)) -> expr (Single a)

Execute a subquery SELECT in an expression.

sub_selectDistinct :: PersistField a => query (expr (Single a)) -> expr (Single a)

Execute a subquery SELECT_DISTINCT in an expression.

(^.) :: (PersistEntity val, PersistField typ) => expr (Entity val) -> EntityField val typ -> expr (Single typ)

Project a field of an entity.

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

Project a field of an entity that may be null.

val :: PersistField typ => typ -> expr (Single typ)

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

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

IS NULL comparison.

just :: expr (Single typ) -> expr (Single (Maybe typ))

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

nothing :: expr (Single (Maybe typ))

NULL value.

countRows :: Num a => expr (Single a)

COUNT(*) value.

not_ :: expr (Single Bool) -> expr (Single Bool)

(==.) :: PersistField typ => expr (Single typ) -> expr (Single typ) -> expr (Single Bool)

(>=.) :: PersistField typ => expr (Single typ) -> expr (Single typ) -> expr (Single Bool)

(>.) :: PersistField typ => expr (Single typ) -> expr (Single typ) -> expr (Single Bool)

(<=.) :: PersistField typ => expr (Single typ) -> expr (Single typ) -> expr (Single Bool)

(<.) :: PersistField typ => expr (Single typ) -> expr (Single typ) -> expr (Single Bool)

(!=.) :: PersistField typ => expr (Single typ) -> expr (Single typ) -> expr (Single Bool)

(&&.) :: expr (Single Bool) -> expr (Single Bool) -> expr (Single Bool)

(||.) :: expr (Single Bool) -> expr (Single Bool) -> expr (Single Bool)

(+.) :: PersistField a => expr (Single a) -> expr (Single a) -> expr (Single a)

(-.) :: PersistField a => expr (Single a) -> expr (Single a) -> expr (Single a)

(/.) :: PersistField a => expr (Single a) -> expr (Single a) -> expr (Single a)

(*.) :: PersistField a => expr (Single a) -> expr (Single a) -> expr (Single a)

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

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 -> expr (Single typ) -> expr (Update val)

(+=.) :: (PersistEntity val, PersistField a) => EntityField val a -> expr (Single a) -> expr (Update val)

(-=.) :: (PersistEntity val, PersistField a) => EntityField val a -> expr (Single a) -> expr (Update val)

(*=.) :: (PersistEntity val, PersistField a) => EntityField val a -> expr (Single a) -> expr (Update val)

(/=.) :: (PersistEntity val, PersistField a) => EntityField val a -> expr (Single a) -> expr (Update val)

Instances

Esqueleto SqlQuery SqlExpr SqlPersist

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

FROM clause: bring an entity into scope.

The following types implement from:

• Expr (Entity val), which brings a single entity into scope.
• Tuples of any other types supported by from. Calling from multiple times is the same as calling from a single time and using a tuple.

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 tuple.

data InnerJoin a b

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

Constructors

a InnerJoin b

Instances

IsJoinKind InnerJoin

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

data CrossJoin a b

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

Constructors

a CrossJoin b

Instances

IsJoinKind CrossJoin

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

data LeftOuterJoin a b

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

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

is translated into

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

Constructors

a LeftOuterJoin b

Instances

IsJoinKind LeftOuterJoin

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

data RightOuterJoin a b

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

Constructors

a RightOuterJoin b

Instances

IsJoinKind RightOuterJoin

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

data FullOuterJoin a b

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

Constructors

a FullOuterJoin b

Instances

IsJoinKind FullOuterJoin

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

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

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 FullOuterJoin

IsJoinKind RightOuterJoin

IsJoinKind LeftOuterJoin

IsJoinKind CrossJoin

IsJoinKind InnerJoin

data OnClauseWithoutMatchingJoinException

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

Constructors

OnClauseWithoutMatchingJoinException String

Instances

Eq OnClauseWithoutMatchingJoinException

Ord OnClauseWithoutMatchingJoinException

Show OnClauseWithoutMatchingJoinException

Typeable OnClauseWithoutMatchingJoinException

Exception OnClauseWithoutMatchingJoinException

data PreprocessedFrom a

(Internal) Phantom type used to process from (see fromStart).

data OrderBy

Phantom type used by orderBy, asc and desc.

data Update typ

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