Use of `get` and `toSqlKey` in persistent - haskell

Question

I'm trying to use persistent-postgresql with servant.
I have a User model.
I want to have an endpoint that takes an id and returns the user with that id.
According to other answers I can use toSqlKey to turn an Int64 into a Key to feed to get.
My function looks like:
oneUser :: Int64 -> App (Entity User)
oneUser userId = do
maybeUser <- runDb $ get $ toSqlKey userId
case maybeUser of
Nothing ->
throwError err404
Just user ->
return user
When I try to compile I get the error Couldn't match expected type ‘PersistEntityBackend (Entity User)’ with actual type ‘SqlBackend’
Use of selectList works fine.
allUsers :: App [Entity User]
allUsers = runDb $ selectList [] []
Please tell me what I'm doing wrong and where I should look in the future for stuff like this. I couldn't find get on hackage/the right version of the library on stackage etc.
runDb looks like:
runDb :: (MonadReader Config m, MonadIO m) => SqlPersistT IO b -> m b
runDb query = do
pool <- asks getPool
liftIO $ runSqlPool query pool
taken from this github project.

Answer 1

The difference is that get ... returns a plain User not an Entity User, so this will work:
altSingleUser :: Int64 -> App User
altSingleUser userid = do
let foo = get (toSqlKey userid) :: SqlPersistT IO (Maybe User)
maybeUser <- runDb $ foo
case maybeUser of
Nothing ->
throwError err404
Just person ->
return person
If you want to return an Entity User, just change the last return statement to:
return $ Entity { entityKey = toSqlKey userid, entityVal = person }