src/Rel8/Query/Aggregate.hs · rel8

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rel8/src/Rel8/Query/Aggregate.hs

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1{-# language FlexibleContexts #-}

2{-# language MonoLocalBinds #-}

4module Rel8.Query.Aggregate

5 ( aggregate

6 , countRows

7 )

8where

10-- base

11import Data.Int ( Int64 )

12import Prelude

14-- opaleye

15import qualified Opaleye.Aggregate as Opaleye

17-- rel8

18import Rel8.Aggregate ( Aggregates )

19import Rel8.Expr ( Expr )

20import Rel8.Expr.Aggregate ( countStar )

21import Rel8.Query ( Query )

22import Rel8.Query.Maybe ( optional )

23import Rel8.Query.Opaleye ( mapOpaleye )

24import Rel8.Table.Opaleye ( aggregator )

25import Rel8.Table.Maybe ( maybeTable )

28-- | Apply an aggregation to all rows returned by a 'Query'.

29aggregate :: Aggregates aggregates exprs => Query aggregates -> Query exprs

30aggregate = mapOpaleye (Opaleye.aggregate aggregator)

33-- | Count the number of rows returned by a query. Note that this is different

34-- from @countStar@, as even if the given query yields no rows, @countRows@

35-- will return @0@.

36countRows :: Query a -> Query (Expr Int64)

37countRows = fmap (maybeTable 0 id) . optional . aggregate . fmap (const countStar)