tailing.hs

{-# LANGUAGE OverloadedStrings #-}

import Database.MongoDB
import Data.UString (u)
import Control.Monad.Trans (liftIO)

main = do
   ee <- runNet $ do
      conn <- connect (host "127.0.0.1")
      runConn run conn
   return ()

run = useDb "tailing" $ do
   createCollection [Capped, MaxByteSize (1024*1024)] "messages"
   insert "messages" ["by" =: u"me", "body" =: u"hello world!"]
   cur <- find (select [] "messages") {options = [TailableCursor, AwaitData, NoCursorTimeout]}
   monitor cur
   
monitor c = do
  doc <- next c
  liftIO (putStrLn . show $ doc)
  monitor c


-- $ runhaskell tailing.hs 
-- Just [ _id: Oid 4c8d42f3 7a23b03c35000000, by: "me", body: "hello world!"]
-- tailing.hs: server returned empty batch but says more results on server