Persist an entity with a user reference in Yesod? - json

Question

I'm changing my existing Yesod application to run on a SQL backend instead of mongo. The generated table structure is more strict then the mongo backend. Foreign key references should be created correctly on insert.
postFeedingsR :: Handler RepJson
postFeedingsR = do
muser <- maybeAuth
parsedFeeding <- parseJsonBody_ --get content as JSON
let userId = getUserId muser
let feedingWithUser = Feeding (feedingDate parsedFeeding) (feedingSide parsedFeeding) (feedingTime parsedFeeding) (feedingExcrements parsedFeeding) (feedingRemarks parsedFeeding) userId --should be linked to user..
fid <- runDB $ insert feedingWithUser --store in database
--runDB $ update fid [ FeedingUserId =. userId ] --Old mongo style of linking the feeding to the user
sendResponseCreated $ FeedingR fid --return the id
I try to update the Entity I get from parseJsonBody with the user UID from the maybeAuth. However this gives me the following error:
No instance for (aeson-0.6.0.2:Data.Aeson.Types.Class.FromJSON
(FeedingGeneric backend0))
arising from a use of `parseJsonBody_'
Possible fix:
add an instance declaration for
(aeson-0.6.0.2:Data.Aeson.Types.Class.FromJSON
(FeedingGeneric backend0))
In a stmt of a 'do' block: parsedFeeding <- parseJsonBody_
In the expression:
do { muser <- maybeAuth;
parsedFeeding <- parseJsonBody_;
let userId = getUserId muser;
let feedingWithUser
= Feeding
(feedingDate parsedFeeding)
(feedingSide parsedFeeding)
(feedingTime parsedFeeding)
(feedingExcrements parsedFeeding)
(feedingRemarks parsedFeeding)
userId;
.... }
In an equation for `postFeedingsR':
postFeedingsR
= do { muser <- maybeAuth;
parsedFeeding <- parseJsonBody_;
let userId = ...;
.... }
I'm not sure why this happens. Could anyone put me in the right direction to solve this?

Answer 1

Solved by changing the auth line to:
Entity uid u <- requireAuth
and by adding the function:
addUserToFeeding :: UserId -> Feeding -> Feeding
addUserToFeeding uid Feeding {feedingDate=date, feedingSide=side, feedingTime=time, feedingExcrements=ex, feedingRemarks=remarks} = Feeding date side time ex remarks uid
to create a new Feeding with associated user. This Feeding can then be stored in the normal way in Yesod:
let feedingWithUser = addUserToFeeding uid parsedFeeding
fid <- runDB $ insert feedingWithUser --store in database