src/Rel8/Query/Rebind.hs · rel8

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rel8/src/Rel8/Query/Rebind.hs

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1{-# language FlexibleContexts #-}

3module Rel8.Query.Rebind

4 ( rebind

5 )

6where

8-- base

9import Prelude

11-- opaleye

12import qualified Opaleye.Internal.PackMap as Opaleye

13import qualified Opaleye.Internal.PrimQuery as Opaleye

14import qualified Opaleye.Internal.QueryArr as Opaleye

15import qualified Opaleye.Internal.Tag as Opaleye

16import qualified Opaleye.Internal.Unpackspec as Opaleye

18-- rel8

19import Rel8.Expr ( Expr )

20import Rel8.Query ( Query( Query ) )

21import Rel8.Table ( Table )

22import Rel8.Table.Opaleye ( unpackspec )

25-- | 'rebind' takes a variable name, some expressions, and binds each of them

26-- to a new variable in the SQL. The @a@ returned consists only of these

27-- variables. It's essentially a @let@ binding for Postgres expressions.

28rebind :: Table Expr a => String -> a -> Query a

29rebind prefix a = Query $ \_ -> Opaleye.QueryArr $ \(_, tag) ->

30 let

31 tag' = Opaleye.next tag

32 (a', bindings) = Opaleye.run $

33 Opaleye.runUnpackspec unpackspec (Opaleye.extractAttr prefix tag) a

34 in

35 ((mempty, a'), \_ -> Opaleye.Rebind True bindings, tag')