[web-devel] [ Newbie ] [ MongoDB ] Using MongoDB Persistent backend

[Greg Weber]

The latest version of persistent-mongoDB on hackage works now. After we get
some more usage it will be added as a scaffolding option. Here is some basic
runner code:

import Database.Persist.MongoDB
import Database.MongoDB.Connection
import qualified Database.MongoDB as DB

runMongo :: MongoDBReader (GGHandler M M IO) a -> GHandler M M a
runMongo x = liftIOHandler $
  withMongoDBConn (DB.Database "test") "127.0.0.1" $ runMongoDBConn x
DB.safe DB.Master

On Thu, Jun 30, 2011 at 11:26 AM, Michael Snoyman <michael at snoyman.com>wrote:

> OK, simple question: why can't we use a type of MongoDBReader of:
>
> newtype MongoDBReader m a = MongoDBReader (Action m a)
>    deriving (Monad, Trans.MonadIO, Functor, Applicative)
>
> Michael
>
> On Thu, Jun 30, 2011 at 6:55 PM, Greg Weber <greg at gregweber.info> wrote:
> > I think it is about time to finally fix this. I am probably the least
> > knowledgeable about Monad mashing, but seems like a good time to learn!
> > Here is a simple app we can use:
> > https://gist.github.com/1056520
> > But maybe it is best to use the test suite. Here are all the hacks to get
> > the tests to run right now that need to be removed:
> > instance Context DB.MasterOrSlaveOk IO where
> >   context = undefined
> >   push = undefined
> > instance Context DB.Database IO where
> >   context = undefined
> >   push = undefined
> > instance Context DB.WriteMode IO where
> >   context = undefined
> >   push = undefined
> > instance Context DB.Pipe IO where
> >   context = undefined
> >   push = undefined
> > instance Control.Monad.Throw.Throw DB.Failure IO where
> >   throw = undefined
> >   catch = undefined
> >
> > On Wed, Jun 29, 2011 at 1:25 AM, Michael Snoyman <michael at snoyman.com>
> > wrote:
> >>
> >> On Wed, Jun 29, 2011 at 11:17 AM, Kamil Ciemniewski
> >> <ciemniewski.kamil at gmail.com> wrote:
> >> > Hi all,
> >> >
> >> > I've got some "newbie" problems using MongoDB as backend
> >> > in Persistent.
> >> >
> >> > Basically I've got my app type defined as:
> >> > data MyApp = MyApp
> >> >     { getStatic :: Static -- ^ Settings for static file serving.
> >> >     , connPool :: ConnPool Host
> >> >     }
> >> >
> >> > And I made it an instance of YesodPersist by:
> >> > instance YesodPersist MyApp where
> >> >   type YesodDB MyApp = MongoDBReader Host
> >> >   runDB db = liftIOHandler
> >> >            $ fmap connPool getYesod >>= (\p -> return (p,
> "localhost"))
> >> > >>=
> >> > runMongoDBConn db
> >> >
> >> > And I made it an instance of YesodAuth as well by:
> >> > instance YesodAuth MyApp where
> >> >   type AuthId MyApp = UserId
> >> >
> >> >   loginDest _ = RootR
> >> >   logoutDest _ = RootR
> >> >
> >> >   getAuthId creds = runDB $ do
> >> >       x <- getBy $ UniqueUser $ credsIdent creds
> >> >       case x of
> >> >       Just (uid, _) -> return $ Just uid
> >> >       Nothing -> do
> >> >           fmap Just $ insert $ User (credsIdent creds) Nothing
> >> >
> >> >   authPlugins = [ authEmail ]
> >> >
> >> > I've defined User model as yesod scaffold tool defines it.
> >> >
> >> > Now, when I try to compile it i get:
> >> >
> >> > No instances for (Control.Monad.Context.Context
> >> >                         Database.MongoDB.Connection.MasterOrSlaveOk
> >> >                         (GGHandler s MyApp IO),
> >> >                       Control.Monad.Context.Context
> >> >                         Database.MongoDB.Query.Database (GGHandler s
> >> > MyApp
> >> > IO),
> >> >                       Control.Monad.Context.Context
> >> >                         Database.MongoDB.Internal.Protocol.Pipe
> >> > (GGHandler s
> >> > MyApp IO),
> >> >                       Control.Monad.Context.Context
> >> >                         Database.MongoDB.Query.WriteMode (GGHandler s
> >> > MyApp
> >> > IO),
> >> >                       Control.Monad.Throw.Throw
> >> >                         Database.MongoDB.Query.Failure (GGHandler s
> >> > MyApp
> >> > IO))
> >> >       arising from a use of `insert'
> >> >     Possible fix:
> >> >       add instance declarations for
> >> >       (Control.Monad.Context.Context
> >> >          Database.MongoDB.Connection.MasterOrSlaveOk
> >> >          (GGHandler s MyApp IO),
> >> >        Control.Monad.Context.Context
> >> >          Database.MongoDB.Query.Database (GGHandler s MyApp IO),
> >> >        Control.Monad.Context.Context
> >> >          Database.MongoDB.Internal.Protocol.Pipe (GGHandler s MyApp
> IO),
> >> >        Control.Monad.Context.Context
> >> >          Database.MongoDB.Query.WriteMode (GGHandler s MyApp IO),
> >> >        Control.Monad.Throw.Throw
> >> >          Database.MongoDB.Query.Failure (GGHandler s MyApp IO))
> >> >     In the expression: insert
> >> >     In the second argument of `($)', namely
> >> >       `insert $ User (credsIdent creds) Nothing'
> >> >     In the expression:
> >> >         fmap Just $ insert $ User (credsIdent creds) Nothing
> >> >
> >> > The problem is probably very trivial.. But I've got no ideas how to
> fix
> >> > it.
> >> >
> >> > Best regards
> >> > Kamil Ciemniewski
> >> >
> >> > _______________________________________________
> >> > web-devel mailing list
> >> > web-devel at haskell.org
> >> > http://www.haskell.org/mailman/listinfo/web-devel
> >> >
> >> >
> >>
> >> I don't have direct experience with the MongoDB backend, but I can
> >> give this a shot if I saw some code. I think one possibility would be
> >> to wrap everything in a liftIO, but then you won't have access to the
> >> Handler monad features. This would prevent you from doing things like
> >> setting messages and sending redirects from the database access
> >> itself, but should otherwise be fine.
> >>
> >> Michael
> >>
> >> _______________________________________________
> >> web-devel mailing list
> >> web-devel at haskell.org
> >> http://www.haskell.org/mailman/listinfo/web-devel
> >
> >
>
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