Why PFRelation does not support fromLocalDataStore

问题:

I have a PFUser object with several PFRelation pointing to other objects. When I run the following code:

PFRelation *relation = [[PFUser currentUser] relationForKey:@"Relation"];
PFQuery *query = [relation query];
[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error){
    NSLog(@"%@", objects);
}];

it works fine. However, when I want to do the same from the local data store:

PFRelation *relation = [[PFUser currentUser] relationForKey:@"Relation"];
PFQuery *query = [[relation query] fromLocalDataStore]; // !!!
[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error){
    NSLog(@"%@", objects);
}];

it returns nothing, despite the fact I've pinned both my user and related objects with [myObject pinInBackground].

Why PFRelation queries does not support fromLocalDataStore? What I'm doing wrong?

回答1:

I've created a bug report for this issue which is

escalated to the engineering team to investigate further

So it looks like it's a bug

In the meanwhile, I've converted all my PFRelations to arrays of pointers to related PFObjects. Not as fancy as PFRelation, but works fine with local data storage.

Update: parse solved the issue in Parse SDK v.1.7.3

回答2:

It's a Parse bug. It can be also reproduced with Android SDK. I'm not sure on iOS, but on Android I have found a way how to make it work.

You need to have a Pointer in "related" classes to the ParseObject which has Relations.

In your case, you have a PFUser which has several PFRelations. If you add a PFPointer to your PFUser in "related" classes, query from the local datastore would work just fine.

Or for the case from my link above - If Comment class would have a Pointer to a Post class everything would work fine.

回答3:

Have the same problem in parse 1.7.5 (release notes mentions that they fixed this bug, but still not working for me)

You can make it working with executing separate query for relation you have for each pinning object (maybe there is a way to do it with all objects at once?). And then pin results of relation query.

After that querying from local datastore starts working fine.