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( E ) )

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

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

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

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 {} -> I $ case hfield exprs field of

32 E expr -> Value expr

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

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

37-- override whatever is in the input expression.

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

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

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

42-- with a call to @DEFAULT@.

43toInsertDefaults :: Inserts exprs inserts => exprs -> inserts

44toInsertDefaults (toColumns -> exprs) = fromColumns $ htabulate $ \field ->

45 case hfield hspecs field of

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

47 E expr -> I $ case necessity of

48 SRequired -> Value expr

49 SOptional -> Default