Adding Authentication to existing Yesod project with Haskell - haskell

Question

I have been using this guide in order to add authentication and authorisation to my project. I am new to Yesod and have been running into some problems:
I am using the following foundation data:
data App = App (TChan Text)
For my authentication i need this data type:
data App = App SqlBackend
How can i combine the two? Do i then also have to change existing functions?
In the end i run everything like this:
main :: IO ()
main = runNoLoggingT $ withSqliteConn "email.db3" $ \conn -> liftIO $ do
runSqlConn (runMigration migrateAll) conn
chan <- newTChanIO
warp 3000 $ App chan
-- Backend SqlBackend needs to be initilized with conn (see below)
{- OLD
main = do
chan <- newTChanIO
warp 3000 $ App chan
-}
{- NEW
main = runNoLoggingT $ withSqliteConn "email.db3" $ \conn -> liftIO $ do
runSqlConn (runMigration migrateAll) conn
warp 3000 $ App conn
-}
I know that i have to combine the two. I read this article. How do i get chan and also conn together? It might sound trivial, but there is little documentation out there.
Please help me!

Answer 1

Typically people make their App datatype a record with multiple fields. For example, the scaffolded Yesod project uses this code:
data App = App
{ appSettings :: AppSettings
, appStatic :: Static -- ^ Settings for static file serving.
, appConnPool :: ConnectionPool -- ^ Database connection pool.
, appHttpManager :: Manager
, appLogger :: Logger
}
The example code you linked to does that as well:
data App = App
{ homepageContent :: Html
, visitorCount :: IORef Int
}
So what about something like this:
-- Small caveat: this is code untested
data App = App
{ backend :: SqlBackend
, chan :: TChan Text
}
main :: IO ()
main = do
chan <- newTChanIO
runNoLoggingT $ withSqliteConn "email.db3" $ \conn -> liftIO $ do
runSqlConn (runMigration migrateAll) conn
warp 3000 $ App { backend=conn, chan=chan}
You would have to change old code accessing your TChan, but once your App is a record, you can add more fields without making changes to the rest of your codebase.
As a side note, have you considered using the Yesod scaffolding? You'd start off with all this handled for you, with a bunch of other niceties and best practices already implemented for you.