src/Rel8/Table/Order.hs · rel8

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rel8/src/Rel8/Table/Order.hs

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1{-# language DataKinds #-}

2{-# language NamedFieldPuns #-}

3{-# language ScopedTypeVariables #-}

4{-# language TypeApplications #-}

5{-# language TypeFamilies #-}

7module Rel8.Table.Order

8 ( ascTable

9 , descTable

10 )

11where

13-- base

14import Data.Functor.Const ( Const( Const ), getConst )

15import Data.Functor.Contravariant ( (>$<), contramap )

16import Prelude

18-- rel8

19import Rel8.Expr.Order ( asc, desc, nullsFirst, nullsLast )

20import Rel8.Order ( Order )

21import Rel8.Schema.Dict ( Dict( Dict ) )

22import Rel8.Schema.HTable (htabulateA, hfield, hspecs)

23import Rel8.Schema.Null ( Nullity( Null, NotNull ) )

24import Rel8.Schema.Spec ( Spec( Spec, nullity ) )

25import Rel8.Table ( Columns, toColumns )

26import Rel8.Table.Ord ( OrdTable, ordTable )

29-- | Construct an 'Order' for a 'Table' by sorting all columns into ascending

30-- orders (any nullable columns will be sorted with @NULLS FIRST@).

31ascTable :: forall a. OrdTable a => Order a

32ascTable = contramap toColumns $ getConst $

33 htabulateA @(Columns a) $ \field -> case hfield hspecs field of

34 Spec {nullity} -> case hfield (ordTable @a) field of

35 Dict -> Const $ (`hfield` field) >$<

36 case nullity of

37 Null -> nullsFirst asc

38 NotNull -> asc

41-- | Construct an 'Order' for a 'Table' by sorting all columns into descending

42-- orders (any nullable columns will be sorted with @NULLS LAST@).

43descTable :: forall a. OrdTable a => Order a

44descTable = contramap toColumns $ getConst $

45 htabulateA @(Columns a) $ \field -> case hfield hspecs field of

46 Spec {nullity} -> case hfield (ordTable @a) field of

47 Dict -> Const $ (`hfield` field) >$<

48 case nullity of

49 Null -> nullsLast desc

50 NotNull -> desc