src/Rel8/Table/Insert.hs · rel8

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rel8/src/Rel8/Table/Insert.hs

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1{-# language FlexibleContexts #-}

2{-# language NamedFieldPuns #-}

3{-# language TypeFamilies #-}

4{-# language ViewPatterns #-}

6module Rel8.Table.Insert

7 ( toInsert

8 , toInsertDefaults

9 )

10where

12-- base

13import Prelude

15-- rel8

16import Rel8.Expr ( Col(..) )

17import Rel8.Kind.Necessity ( SNecessity( SOptional, SRequired ) )

18import Rel8.Schema.HTable ( hfield, htabulate, hspecs )

19import Rel8.Schema.Insert ( Inserts, Col(..) )

20import Rel8.Schema.Spec ( SSpec(..) )

21import Rel8.Table ( fromColumns, toColumns )

24-- | @toInsert@ converts a 'Table' of 'Expr's into a 'Table' that can be used

25-- with 'Rel8.insert'. This will override any columns that have default values

26-- to use exactly what is given. If you want to use default values, you can

27-- either override the result of @toInsert@, or use 'toInsertDefaults'.

28toInsert :: Inserts exprs inserts => exprs -> inserts

29toInsert (toColumns -> exprs) = fromColumns $ htabulate $ \field ->

30 case hfield hspecs field of

31 SSpec {necessity} -> case hfield exprs field of

32 DB expr -> case necessity of

33 SRequired -> RequiredInsert expr

34 SOptional -> OptionalInsert (Just expr)

37-- | @toInsertDefaults@ converts a 'Table' of 'Expr's into a 'Table' that can

38-- be used with 'Rel8.insert'. Any columns that have a default value will

39-- override whatever is in the input expression.

41-- One example where this is useful is for any table that has a special @id@

42-- column, which has a default value to draw a new value from a sequence. If we

43-- use 'toInsertDefaults', we can provide a dummy value that will be replaced

44-- with a call to @DEFAULT@.

45toInsertDefaults :: Inserts exprs inserts => exprs -> inserts

46toInsertDefaults (toColumns -> exprs) = fromColumns $ htabulate $ \field ->

47 case hfield hspecs field of

48 SSpec {necessity} -> case hfield exprs field of

49 DB expr -> case necessity of

50 SRequired -> RequiredInsert expr

51 SOptional -> OptionalInsert Nothing