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Add EXTRACT function to Rel8.Expr.Time #237

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Add EXTRACT function to Rel8.Expr.Time #237

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26 changes: 24 additions & 2 deletions src/Rel8/Expr/Time.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,7 @@ module Rel8.Expr.Time
, addTime
, diffTime
, subtractTime
, unsafeExtractFromTime

-- * Working with @CalendarDiffTime@
, scaleInterval
Expand All @@ -24,6 +25,7 @@ module Rel8.Expr.Time
, week, weeks
, month, months
, year, years
, unsafeExtractFromInterval
) where

-- base
Expand All @@ -32,8 +34,10 @@ import Prelude

-- rel8
import Rel8.Expr ( Expr )
import Rel8.Expr.Function (binaryOperator, function)
import Rel8.Expr.Opaleye ( castExpr, unsafeCastExpr, unsafeLiteral )
import Rel8.Expr.Function ( binaryOperator, function )
import Rel8.Expr.Opaleye ( castExpr, unsafeCastExpr, unsafeLiteral, fromPrimExpr, toPrimExpr )
import Rel8.Type ( DBType )
import qualified Opaleye.Internal.HaskellDB.PrimQuery as Opaleye

-- time
import Data.Time.Calendar ( Day )
Expand Down Expand Up @@ -90,6 +94,14 @@ diffTime = binaryOperator "-"
subtractTime :: Expr CalendarDiffTime -> Expr UTCTime -> Expr UTCTime
subtractTime = flip (binaryOperator "-")

-- | Extract a part of a point in time. See possibilities
-- [here](https://www.postgresqltutorial.com/postgresql-date-functions/postgresql-extract/).
-- This function is unsafe because you must decide yourself the output type.
unsafeExtractFromTime :: DBType a => String -> Expr UTCTime -> Expr a
unsafeExtractFromTime name expr =
castExpr $
fromPrimExpr $
Opaleye.FunExpr "EXTRACT" [Opaleye.FunExpr (name <> " FROM") [toPrimExpr expr]]

scaleInterval :: Expr Double -> Expr CalendarDiffTime -> Expr CalendarDiffTime
scaleInterval = binaryOperator "*"
Expand Down Expand Up @@ -167,3 +179,13 @@ years = (`scaleInterval` year)

singleton :: String -> Expr CalendarDiffTime
singleton unit = castExpr $ unsafeLiteral $ "'1 " ++ unit ++ "'"

-- | Extract a part of an interval. See possibilities
-- [here](https://www.postgresqltutorial.com/postgresql-date-functions/postgresql-extract/).
-- This function is unsafe because you must decide yourself the output type.
unsafeExtractFromInterval :: DBType a => String -> Expr CalendarDiffTime -> Expr a
unsafeExtractFromInterval name expr =
castExpr $
fromPrimExpr $
Opaleye.FunExpr "EXTRACT" [Opaleye.FunExpr (name <> " FROM") [toPrimExpr expr]]