src/Rel8/Schema/Column.hs · rel8

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rel8/src/Rel8/Schema/Column.hs

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1{-# language DataKinds #-}

2{-# language TypeFamilies #-}

3{-# language StandaloneKindSignatures #-}

5module Rel8.Schema.Column

6 ( Column, Default

7 )

8where

10-- base

11import Data.Kind ( Type )

12import Prelude ()

14-- rel8

15import Rel8.Kind.Necessity ( Necessity( Required, Optional ) )

16import Rel8.Schema.Field ( Field )

17import qualified Rel8.Schema.Kind as K

20type Default :: Type -> Type

21data Default a

24type GetNecessity :: Type -> Necessity

25type family GetNecessity a where

26 GetNecessity (Default _) = 'Optional

27 GetNecessity _ = 'Required

30type UnwrapDefault :: Type -> Type

31type family UnwrapDefault a where

32 UnwrapDefault (Default a) = a

33 UnwrapDefault a = a

36-- | The @Column@ type family should be used to indicate which fields of your

37-- data types are single columns in queries. This type family has special

38-- support when a query is executed, allowing you to use a single data type for

39-- both query data and rows decoded to Haskell.

40type Column :: K.Context -> Type -> Type

41type Column context a =

42 Field context (GetNecessity a) (UnwrapDefault a)