streamSqlite.hs

streamSqlite.hs

#!/usr/bin/env stack
{-      stack
        script
        --resolver lts-18.28
        --package sqlite-simple
        --package async
        --package text
-}
{-
-- | the purpose of this code is to make sure sqlite maybe accessed concurrently
-- Requires stack and sqlite
-}
{-# LANGUAGE OverloadedStrings #-}

import System.IO
import           Control.Concurrent.Async       (concurrently, forConcurrently)
import Control.Monad ( void )
import Database.SQLite.Simple.FromRow
import           Database.SQLite.Simple


data TestField = TestField Int String deriving (Show)

q :: Query
q =  "SELECT * from test where str=:str"
dbAction1 :: Connection -> Int -> IO [TestField]
dbAction1 conn num = do
  let
    f :: [TestField] -> TestField -> IO [TestField]
    f ts t = appendFile "streamOut.txt" (show t) >> pure (t:ts)
  fold_ conn "select * from test" [] f
instance FromRow TestField where
  fromRow = TestField <$> field <*> field

instance ToRow TestField where
  toRow (TestField i s) =  toRow (i, s)

main :: IO ()
main = do
  conn <- open "/tmp/test.db"
  res <- (dbAction1 conn 1)
  print res

  close conn

  putStrLn "\n------ completed sqlite stuff ----\n"