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Document distinctOn and distinctOnBy

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This commit is contained in:
Ollie Charles 2021-03-24 13:08:37 +00:00
parent f137cd0dac
commit b76ed4d111
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6
src/Rel8/Query/Distinct.hs
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@ -32,11 +32,17 @@ distinct :: EqTable a => Query a -> Query a
distinct = mapOpaleye (Opaleye.distinctExplicit distinctspec)
-- | Select all distinct rows from a query, where rows are equivalent according
-- to a projection. If multiple rows have the same projection, it is
-- unspecified which row will be returned. If this matters, use 'distinctOnBy'.
distinctOn :: EqTable b => (a -> b) -> Query a -> Query a
distinctOn proj =
mapOpaleye (\q -> Opaleye.productQueryArr (Opaleye.distinctOn unpackspec proj . Opaleye.runSimpleQueryArr q))
-- | Select all distinct rows from a query, where rows are equivalent according
-- to a projection. If there are multiple rows with the same projection, the
-- first row according to the specified 'Order' will be returned.
distinctOnBy :: EqTable b => (a -> b) -> Order a -> Query a -> Query a
distinctOnBy proj (Order order) =
mapOpaleye (\q -> Opaleye.productQueryArr (Opaleye.distinctOnBy unpackspec proj order . Opaleye.runSimpleQueryArr q))