There are excellent libraries that I want to make interoperable with MFlow one of them is Persistent. It allows to define backend-independent data layers. In the previous post I mentioned an example of direct integration of TCache -the cache of MFlow- with Amazon web services. In this example I will show how MFlow and Persistent directly interact.
Since in this case, the database is a in memory instance of sqlite, It does not make sense to cache data. But since Persistent can interact with remote SQL and nonSQL databases, I need to integrate TCache with Persistent for caching in the near future.
But first, this example illustrates the use of MFlow with Persistent. The example is at:
The code is taken from http://www.yesodweb.com/book/persistent by modifying the first example and making some guesses by looking at the prostgresSQL version , both are console-oriented programs.
Note how little additions are necessary to change a console application of the sample to a MFlow application.
The example has a navigation of four pages and you can go forward and backward. While the flow looks like an ordinary imperative program, yo can go back and fort and to introduce any bookmark without producing navigation errors.
Additionally you can press the back button, change the form input and see how the responses match the register values.
This is the code:
{-# LANGUAGE EmptyDataDecls #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE QuasiQuotes #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE NoMonomorphismRestriction #-}
module MFlowPersistent
where
import MFlow.Wai.Blaze.Html.All
import Control.Monad.IO.Class (liftIO)
import Database.Persist
import Database.Persist.Sqlite
import Database.Persist.TH
import System.IO.Unsafe
import Menu
share [mkPersist sqlSettings, mkMigrate "migrateAll"] [persistLowerCase|
Person
name String
age Int Maybe
deriving Show
BlogPost
title String
authorId PersonId
deriving Show
|]
-- Uncomment this to run the example alone
--main= do
-- migratesqlite
-- runNavigation "" . transientNav $ mFlowPersistent
--
--askm= ask
pool= unsafePerformIO $ createSqlitePool ":memory:" 10
runSQL sql= liftIO $ runSqlPersistMPool sql pool
migratesqlite= runSQL $ runMigration migrateAll
mFlowPersistent ∷ FlowM Html IO ()
mFlowPersistent = do
(name, age) ← askm $ (,)
<$> getString Nothing <! hint "your name"
<++ br
<*> getInt Nothing <! hint "your age"
<** br
++> submitButton "enter"
userId ← runSQL $ insert $ Person name $ Just age
post ← askm $ getString Nothing <! hint "your post" <** submitButton "enter"
runSQL $ insert $ BlogPost post userId
oneUserPost ← runSQL $ selectList [BlogPostAuthorId ==. userId] [LimitTo 1]
askm $ b << show (oneUserPost ∷ [Entity BlogPost])
++> br
++> wlink () << b "click here"
user ← runSQL $ get userId
askm $ b << show (user ∷ Maybe Person)
++> br ++> wlink () << b "click here"
where
hint h= [("placeholder",h)]
