practice: Database.Persist

test_persist_mysql.hs

{-# LANGUAGE QuasiQuotes, TemplateHaskell, TypeFamilies, OverloadedStrings #-}
{-# LANGUAGE GADTs, FlexibleContexts #-}
import Database.Persist
import Database.Persist.MySQL
import Database.Persist.TH
import Control.Monad.IO.Class (liftIO)

import Data.Conduit
import qualified Data.Conduit.List as CL

import Data.ByteString (ByteString)
import qualified Data.ByteString as BS
import Data.ByteString.Char8 as BC (pack)

share [mkPersist sqlSettings, mkMigrate "migrateAll"] [persist|
Person
  name  String
  age   Int Maybe
  deriving Show
|]

main :: IO ()
main = withMySQLConn defaultConnectInfo $ runSqlConn $ do
  runMigration migrateAll

  insert $ Person "AAA" $ Just 35
  insert $ Person "BBB" $ Just 20
  insert $ Person "CCC" $ Just 40

  runResourceT $ do
    selectSource [] [Asc PersonAge, LimitTo 10] $$ showEntity

showEntity :: Sink (Entity Person) (ResourceT (SqlPersist IO)) ()
showEntity = do
  entity <- CL.head
  case entity of
    Just p  -> do
      liftIO $ BS.putStrLn . BC.pack . show $ p
      showEntity
    Nothing -> return ()