postgresql-simple

postgresql-simple.hs

{-# LANGUAGE RecordWildCards #-}
{-# LANGUAGE OverloadedStrings #-}

import Control.Monad.State
import Control.Monad.Reader
import Data.Text
import Database.PostgreSQL.Simple
import Database.PostgreSQL.Simple.FromRow
import Database.PostgreSQL.Simple.ToRow
import Data.Maybe (fromJust)

data BoardGame = BoardGame
    { name :: Text
    , designer :: Text
    , year :: Maybe Int
    } deriving (Show, Eq)

instance FromRow BoardGame where
    fromRow = BoardGame <$> field <*> field <*> field

instance ToRow BoardGame where
    toRow BoardGame{..} = toRow (name, designer, year)

createGame :: BoardGame -> ReaderT Connection IO (Int, BoardGame)
createGame game = ask >>= \conn -> do
    [Only boardGameId] <- liftIO $ query
        conn 
        "INSERT INTO board_games (name, designer, year) VALUES (?,?,?) RETURNING id"
        game
    game' <- fromJust <$> readGame boardGameId
    pure (boardGameId, game')

readGame :: Int -> ReaderT Connection IO (Maybe BoardGame)
readGame boardGameId = ask >>= \conn -> do
    games <- liftIO $ query 
        conn
        "SELECT name, designer, year FROM board_games WHERE id = ?"
        (Only boardGameId)
    pure $ case games of
         [g] -> Just g
         _ -> Nothing

main :: IO ()
main = do
    conn <- connectPostgreSQL "host=localhost port=5432 connect_timeout=10"
    flip runReaderT conn $ do
        result <- createGame $ BoardGame
            "Cosmic Encounter"
            "Bill Eberle"
            (Just 2008)
        liftIO $ print result