Nested to-many relationships with RestKit - ios

Question

I'm trying to map relationships for the following JSON to a CoreData backed model.
Here's the JSON:
{
"photos": [
{
"id": 1,
"thumb": "http://localhost/test_1_thumb.png",
"image": "http://localhost/test_1.png",
"date": "2011-07-02T06:06:16Z",
"likes": 0,
"user": {
"id": 1,
"username": "User1",
"avatar": "http://cdn.domain.com/avatar.jpg"
},
"comments": [
{
"date": "2011-07-02T06:06:16Z",
"text": "This is the only comment",
"id": 1,
"author": {
"username": "User1",
"id": 1,
"avatar": "http://cdn.domain.com/avatar.jpg"
}
}
]
}
]
}
My CoreData models which I've mapped with RestKit's OM2 classes.
The Photo class.
#interface Photo : NSManagedObject
#property (nonatomic, retain) NSString * thumbnailUrl;
#property (nonatomic, retain) NSString * imageUrl;
#property (nonatomic, retain) NSDate * date;
#property (nonatomic, retain) NSNumber * likes;
#property (nonatomic, retain) NSNumber * photoID;
#property (nonatomic, retain) User *owner;
#property (nonatomic, retain) NSSet *comments;
#end
#interface Photo (CoreDataGeneratedAccessors)
- (void)addCommentsObject:(Comment *)value;
- (void)removeCommentsObject:(Comment *)value;
- (void)addComments:(NSSet *)values;
- (void)removeComments:(NSSet *)values;
#end
#implementation Photo
#dynamic thumbnailUrl;
#dynamic imageUrl;
#dynamic date;
#dynamic likes;
#dynamic photoID;
#dynamic owner;
#dynamic comments;
#end
Now the part I'm not completely sure on is the relationships:
// Map relationships between entities.
[commentMapping mapKeyPath:#"author" toRelationship:#"author" withMapping:userMapping];
[photoMapping mapKeyPath:#"user" toRelationship:#"owner" withMapping:userMapping];
[photoMapping mapKeyPath:#"comments" toRelationship:#"comments" withMapping:commentMapping];
With this I'm able to access all but the comments attribute of a photo, with this error: Comments = Relationship 'comments' fault on managed object. I have a feeling this is to do with the Photo model having comments defined as an NSSet or I'm doing something wrong with the relationship mapping but I'm not sure.

Answer 1

So turns out that the problem was nothing to do with RestKit or the mapping but my understanding of how CoreData functions.
I was accessing the mapped JSON objects in my delgate as follows:
- (void)objectLoader:(RKObjectLoader*)objectLoader didLoadObjects:(NSArray*)objects {
NSLog(#"Loaded photos: %#", objects);
for (id object in objects) {
Photo *photo = object;
// Print other photo attributes...
NSLog(#"Comments = %#", photo.comments );
}
}
The problem was in trying to print the collection object directly. CoreData would not fire a fault on the data store. Simply replacing with a fast iteration as follows and accessing the properties allowed me to access the comments object.
for (Photo *photo in objects) {
for (Comment *comment in photo.comments) NSLog(#"Comment = %#", comment.text);
}

Answer 2

You need something like:
[objectManager.mappingProvider setMapping:commentMapping forKeyPath:#"comments"];
Also checkout
https://github.com/RestKit/RestKit/wiki/Object-mapping