persistent page. Couldn't match type `BaseBackend backend0' with `SqlBackend'

[ghost]

Hello,

When I run the first code from the persistent page I see this error appear,

* Couldn't match type `BaseBackend backend0' with `SqlBackend'
        arising from a use of `runSqlite'
      The type variable `backend0' is ambiguous
    * In the expression: runSqlite ":memory:"
      In the expression:
        runSqlite ":memory:"
          $ do michaelId <- insert $ Person "Michael" $ Just 26
               michael <- get michaelId
               liftIO $ print michael
      In an equation for `main':
          main
            = runSqlite ":memory:"
                $ do michaelId <- insert $ Person "Michael" $ Just 26
                     michael <- get michaelId
                     liftIO $ print michael
   |
24 | main = runSqlite ":memory:" $ do

I can make a PR how to solve this but I need to know where this page can be found.

[snoyberg]

It looks like this line has a type signature that doesn't belong:

runMigration migrateAll :: IO () Do you want to try PRing a fix?

On Wed, Jul 18, 2018 at 11:23 PM RoelofWobben notifications@github.com wrote:

Hello,

When I run the first code from the persistent page I see this error appear,

• Couldn't match type BaseBackend backend0' withSqlBackend' arising from a use of runSqlite' The type variablebackend0' is ambiguous
  • In the expression: runSqlite ":memory:" In the expression: runSqlite ":memory:" $ do michaelId <- insert $ Person "Michael" $ Just 26 michael <- get michaelId liftIO $ print michael In an equation for `main': main = runSqlite ":memory:" $ do michaelId <- insert $ Person "Michael" $ Just 26 michael <- get michaelId liftIO $ print michael | 24 | main = runSqlite ":memory:" $ do

I can make a PR how to solve this but I need to know where this page can be found.

— You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub https://github.com/yesodweb/yesodweb.com-content/issues/213, or mute the thread https://github.com/notifications/unsubscribe-auth/AADBBzzYNzHJEcpDo5uUWxb4nL-jGtQfks5uH5kjgaJpZM4VVTcI .

[ghost]

Moment, this is the code just before the migration is added. Im talking about this one :

{-# LANGUAGE EmptyDataDecls             #-}
{-# LANGUAGE FlexibleContexts           #-}
{-# LANGUAGE GADTs                      #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE MultiParamTypeClasses      #-}
{-# LANGUAGE OverloadedStrings          #-}
{-# LANGUAGE QuasiQuotes                #-}
{-# LANGUAGE TemplateHaskell            #-}
{-# LANGUAGE TypeFamilies               #-}
import           Control.Monad.IO.Class  (liftIO)
import           Database.Persist
import           Database.Persist.Sqlite
import           Database.Persist.TH

share [mkPersist sqlSettings, mkMigrate "migrateAll"] [persistLowerCase|
Person
    name String
    age Int Maybe
    deriving Show
|]

main :: IO ()
main = runSqlite ":memory:" $ do
    michaelId <- insert $ Person "Michael" $ Just 26
    michael <- get michaelId
    liftIO $ print michael

and I solved it with a little help of the slack channel this way :

runSqlite' :: (MonadUnliftIO m) => Text -> ReaderT SqlBackend (NoLoggingT (ResourceT m)) a -> m a
runSqlite' = runSqlite

main :: IO ()
main = runSqlite' ":memory:" $ do
    michaelId <- insert $ Person "Michael" $ Just 26
    michael <- get michaelId
    liftIO $ print michael

[ghost]

and yes, I can try to make a PR but as I said earlier have to know which file this exactly is.

[snoyberg]

The source is available here:

https://github.com/yesodweb/yesodweb.com-content/blob/master/book/asciidoc/persistent.asciidoc

For future reference, each chapter in the book has a (relatively small) link at the top that says "View source on Github".