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 a v c where

Instances of this type can be converted to Expr. It is useful for uniform manipulation over fields and plain values

Methods

toExpression :: a -> Expr v c a

Instances

PurePersistField a => Expression a v c

(PersistEntity v, Constructor c, FieldLike (u (UniqueMarker v)) (RestrictionHolder v c) a', ~ ((* -> *) -> *) c' (UniqueConstr (Key v' (Unique u))), ~ * v v', IsUniqueKey (Key v' (Unique u)), ~ ((* -> *) -> *) c c') => Expression (u (UniqueMarker v)) v' c'

(PersistEntity v, Constructor c, PersistField (Key v' BackendSpecific), FieldLike (AutoKeyField v c) (RestrictionHolder v c) a', ~ * v v', ~ ((* -> *) -> *) c c') => Expression (AutoKeyField v c) v' c'

(PersistEntity v, Constructor c, PersistField a, ~ * v v', ~ ((* -> *) -> *) c c') => Expression (Arith v c a) v' c'

(PersistEntity v, Constructor c, PersistField a, ~ * v v', ~ ((* -> *) -> *) c c') => Expression (SubField v c a) v' c'

(PersistEntity v, Constructor c, PersistField a, ~ * v v', ~ ((* -> *) -> *) c c') => Expression (Field v c a) v' c'

(=.) :: (Expression b v c, FieldLike f (RestrictionHolder v c) a', Unifiable f b) => f -> b -> Update v c

Update field

(&&.) :: Cond v c -> Cond v c -> Cond v c

Boolean "and" operator.

(||.) :: Cond v c -> Cond v c -> Cond v c

Boolean "or" operator.

(==.) :: (Expression a v c, Expression b v c, Unifiable a b) => a -> b -> Cond v c

(/=.) :: (Expression a v c, Expression b v c, Unifiable a b) => a -> b -> Cond v c

(<.) :: (Expression a v c, Expression b v c, Unifiable a b) => a -> b -> Cond v c

(<=.) :: (Expression a v c, Expression b v c, Unifiable a b) => a -> b -> Cond v c

(>.) :: (Expression a v c, Expression b v c, Unifiable a b) => a -> b -> Cond v c

(>=.) :: (Expression a v c, Expression b v c, Unifiable a b) => a -> b -> Cond v c