Database.Groundhog.Expression

This module provides mechanism for flexible and typesafe usage of plain data values and fields. The expressions can used in conditions and right part of Update statement. Example:

 StringField ==. "abc" &&. NumberField >. (0 :: Int) ||. MaybeField ==. (Nothing :: Maybe String) ||. MaybeField ==. Just "def"

Note that polymorphic values like numbers or Nothing must have a type annotation

Documentation

class Expression db r a where

Instances of this type can be converted to UntypedExpr. It is useful for uniform manipulation over fields, constant values, etc.

Methods

toExpr :: a -> UntypedExpr db r

Instances

PurePersistField a => Expression db r a

(PersistEntity v, IsUniqueKey k, ~ * k (Key v (Unique u)), ~ * (RestrictionHolder v c) r') => Expression db r' (u (UniqueMarker v))

(EntityConstr v c, ~ * (RestrictionHolder v c) r') => Expression db r' (AutoKeyField v c)

(EntityConstr v c, PersistField a, ~ * (RestrictionHolder v c) r') => Expression db r' (SubField v c a)

(EntityConstr v c, PersistField a, ~ * (RestrictionHolder v c) r') => Expression db r' (Field v c a)

(PersistField a, ~ * db' db, ~ * r' r) => Expression db' r' (Expr db r a)

class Unifiable a b

Instances

(Normalize bk a (ak, r), Normalize ak b (bk, r)) => Unifiable a b

Unifiable a a

class (Expression db r a, Unifiable a a') => ExpressionOf db r a a'

This helper class can make type signatures more concise

Instances

(Expression db r a, Unifiable a a') => ExpressionOf db r a a'

(=.) :: (FieldLike f db r a', Expression db r b, Unifiable f b) => f -> b -> Update db r

Update field

(&&.) :: Cond db r -> Cond db r -> Cond db r

Boolean "and" operator.

(||.) :: Cond db r -> Cond db r -> Cond db r

Boolean "or" operator.

(==.) :: (Expression db r a, Expression db r b, Unifiable a b) => a -> b -> Cond db r

(/=.) :: (Expression db r a, Expression db r b, Unifiable a b) => a -> b -> Cond db r

(<.) :: (Expression db r a, Expression db r b, Unifiable a b) => a -> b -> Cond db r

(<=.) :: (Expression db r a, Expression db r b, Unifiable a b) => a -> b -> Cond db r

(>.) :: (Expression db r a, Expression db r b, Unifiable a b) => a -> b -> Cond db r

(>=.) :: (Expression db r a, Expression db r b, Unifiable a b) => a -> b -> Cond db r