Persistent issue #48

Entities.hs

{-# LANGUAGE TemplateHaskell, QuasiQuotes, EmptyDataDecls, TypeFamilies, FlexibleContexts, GADTs, OverloadedStrings #-}
module Entities where

import Database.Persist
import Database.Persist.TH
import Data.Text

share [mkPersist sqlSettings, mkMigrate "migrateAll"] [persist|
Group
  title Text
  UniqueTitle title
|]

test.hs

{-# LANGUAGE OverloadedStrings #-}

import Control.Monad
import Control.Monad.Trans
import Database.Persist
import Database.Persist.Postgresql

import Entities

type DB a = SqlPersist IO a

check :: (Show v, PersistEntity v) => v -> DB (Key SqlPersist v)
check v = do
  r <- insertBy v
  case r of
    Left e -> return (entityKey e)
    Right k -> return k

group = Group "UNKNOWN"

main = do
  withPostgresqlConn "port=5432dbname=this" $ runSqlConn $ do
    r <- check group
    liftIO $ print r