从Parse获取关系用户

Question

I am attempting to determine if the current user is in a relationship with my event.

In other words, I have events that users can join. I store a PFRelation of User in the Event Table.

I have tried

self.event.users.query().getObjectInBackground(withId: currentUser.objectId!, block: { (object, error) in
    if let error = error {
        //The query returned an error
        print(error.localizedDescription)
    } else {
        //The object has been retrieved
        print(object)
    }
})

and

do {
    let user = try self.event.users.query().getObjectWithId(currentUser.objectId!)

    if user == nil {
        currentUser.saveInBackground { (success: Bool, error: Error?) in
            eventsRelation.add(object)
        }

        usersRelation.add(currentUser)
        object.saveInBackground()


    }
} catch {
    print("Unexpected error: \(error).")
}

But these each return the user no matter what. Even if they are not in the relation.

It is as if they are running the query on the whole user table.

How can I run it on just my subset?

Answer 1

The answer is to use the relationship to query on.

See here for more documentation

So the code would look like this:

let usersRelation = event.relation(forKey: "users")

let usersRelationQuery = usersRelation.query()

usersRelationQuery.whereKey("objectId", equalTo: currentUser.objectId!)
usersRelationQuery.findObjectsInBackground(block: { (objects: [PFObject]?, error: Error?) in
    if let error = error {
        print(error.localizedDescription)
    } else if let objects = objects {
        // The find succeeded.
        print("Successfully retrieved \(objects.count) scores.")
        // Do something with the found objects
        for object in objects {
            print(object.objectId as Any)
        }
    }
})

Note that the event variable above is from the database.

If we did not include the whereKey portion, then it would just get the ones in that relationship.