try_postgresql_simple.hs

{-# LANGUAGE DeriveAnyClass    #-}
{-# LANGUAGE DeriveGeneric     #-}
{-# LANGUAGE OverloadedStrings #-}
module Main where

import           Control.Applicative
import           Control.Monad
import           Database.PostgreSQL.Simple
import           GHC.Generics               (Generic)

data User = User { uid :: Int, login :: String}
   deriving (Generic, FromRow, Show)

main :: IO ()
main = do
  conn <- connect defaultConnectInfo {
    connectDatabase = "haskell",
    connectUser = "rabbit"
  }
  putStrLn "2 + 2"
  mapM_ print =<< ( query_ conn "select 2 + 2" :: IO [Only Int] )
  mapM_ print =<< ( query_ conn "select uid, login from users" :: IO [(Int, String)])
  mapM_ print =<< ( query_ conn "select * from users" :: IO [User])
  res <- query_ conn "select u1.*, u2.* from users as u1, users as u2"
  void $ forM res $ \case
    (User uid1 login1) :. (User uid2 login2) -> putStrLn (login1 ++ "-" ++ login2)

-- resolver: lts-14.5

-- packages:
-- - .

-- nix:
  -- pure: false
  -- enable: true
  -- packages: [ postgresql ]