[web-devel] [yesod] using presistance in sub sites

[Michael Snoyman]

On Fri, Jul 1, 2011 at 7:27 PM, Markus Barenhoff <mb at niulabs.com> wrote:
> Hi there!
>
> I'm a bit confused on how to use persistence in a sub site...
>
> I've written this here, which fails to compile:
> https://gist.github.com/1058863
>
> Is it possible at all to define persistence functionality on subsite
> level and then use the masters runDB ?
> Whats best practice here?
>
> I've seen yesod-auth let implement the persistance related stuff over
> a type class in the master ... But I'd like to keep that stuff with
> the subsite...
>
> Ideas, comments anyone?
>
> Thanks
> Markus
>
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It's a good question. The answer is far from intuitive; I played
around with type errors until I got something to work. Hope this
helps:


{-# LANGUAGE MultiParamTypeClasses, TypeFamilies, GeneralizedNewtypeDeriving #-}
{-# LANGUAGE QuasiQuotes, TemplateHaskell, OverloadedStrings #-}
{-# LANGUAGE DeriveDataTypeable, NoMonomorphismRestriction,
FlexibleInstances #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE UndecidableInstances #-}

import Data.Text (Text)
import Language.Haskell.TH.Syntax hiding (lift)
import Yesod


share2 mkPersist (mkMigrate "migrateTest") [persist|
    Test
        foo Text
|]

data TestSite = TestSite

mkYesodSub "TestSite"
    [ ClassP ''YesodPersist [VarT $ mkName "master"]
    , ClassP ''PersistBackend
        [ ConT ''YesodDB
            `AppT` VarT (mkName "master")
            `AppT` (ConT ''GGHandler `AppT` ConT ''TestSite `AppT`
VarT (mkName "master") `AppT` ConT ''IO)
        ]
    ]
  [parseRoutes|
    /insert InsertR POST
  |]


postInsertR :: (YesodPersist master, PersistBackend (YesodDB master
(GGHandler sub master IO))) => GHandler sub master ()
postInsertR = do
  runDB $ insert $ Test "bar"
  return ()

Michael