Question

I am using parse for the backend part of my iPhone App.

We can have a one to many relation in Parse which described in Relational Data.

This code works fine to retrive the data:

PFQuery *query = [PFQuery queryWithClassName:@"Comment"];
PFObject *fetchedComment = [query getObjectWithId:@"0PprArjYi3"];

NSString *content = [fetchedComment objectForKey:@"content"];
printf("%s", [content UTF8String]);

But when I use their codes provided in the Link, it returns null:

PFObject *post = [fetchedComment objectForKey:@"parent"];
[post fetchIfNeededInBackgroundWithBlock:^(PFObject *object, NSError *error) {
          title = [post objectForKey:@"title"];
}];
printf("%s", [title UTF8String]);     // RETURN NULL

Can anybody tell me what is wrong in this code? The problem could be fetchedcomment.

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Addenda

This one also got an exception:

PFQuery *query = [PFQuery queryWithClassName:@"Comment"];
PFObject *fetchedComment = [query getObjectWithId:@"0PprArjYi3"];

PFObject *post = [fetchedComment objectForKey:@"parent"];
NSString *title = [post objectForKey:@"title"];
printf("%s", [title UTF8String]);

Answer 1

The method fetchIfNeededInBackgroundWithBlock is, as the name suggests, performed in background. Your code asks for a fetch and then immediately continues to the printf. At that point in time, the data hasn’t been fetched yet, so title is probably still nil.

You have two options –

1. Use a synchronous method, such as [post fetch]: instead of [parent fetchInBackground…].

   [post fetch];
   title1 = [post objectForKey:@"title"];
   

2. Print the title inside the block that gets executed when the fetchInBackground... method finishes.