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sumTypes.hs
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sumTypes.hs
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{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE QuasiQuotes #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE TypeFamilies #-}
import Control.Monad.IO.Class (liftIO)
import Database.Groundhog.Sqlite
import Database.Groundhog.TH
data Shape
= Circle {radius :: Double}
| Triangle {side1 :: Double, side2 :: Double, angle :: Double}
deriving (Show)
mkPersist
defaultCodegenConfig
[groundhog|
- entity: Shape
constructors: # Any constructors can be adjusted in this list. The order is not important.
- name: Triangle # This declaration just repeats some of the default values and can be removed.
exprName: TriangleConstructor # Just as default.
- name: Circle
fields:
- name: radius
exprName: CircleRadius # The default value defined by naming style was RadiusField
|]
main = withSqliteConn ":memory:" $
runDbConn $ do
let circle = Circle 5
-- Both table for Circle and for Triangle of the Shape datatype are migrated.
runMigration $ migrate circle
k <- insert circle
insert (Circle 10)
let triangle = Triangle 3 4 (pi / 2)
replace k triangle
smallCirclesCount <- count (CircleRadius <. (11 :: Double))
liftIO $ putStrLn $ "Small circles: " ++ show smallCirclesCount
shapes <- selectAll
liftIO $ print (shapes :: [(AutoKey Shape, Shape)])