Using Mantle with Core Data - NSSet and NSArray

Question

I need your help with something, as I can't get my head around this. I'm using Mantle together with CoreData in iOS.

I have relationships defined that look as follows:

Post 1:N Comment

When I pull the data from my REST Service, I create a Mantle Object Post that has a NSMutableArray of Comments in it. This works flawlessly.

I then store this in Core Data, and this is where I don't know whether I am doing things right.

[MTLManagedObjectAdapter managedObjectFromModel:post insertingIntoContext:[self getManagedObjectContext] error:&error];

So I'm doing this to store my post object into Core Data. The Core Data Model has a relationship called "post_has_comments" which is a cascading One-to-Many relationship. So on the object Post I have "posts_has_comments" -> cascading, on my object "Comment" I have a one-to-one relationship with "Nullify".

Afaik, Core Data treats this as a NSSet. What I'm trying to put in is a NSMutableArray though, as Mantle will take care of this (at least thats what a quick look in its source told me).

Unfortunately, when I get the object back from Core Data with

Post* post = [MTLManagedObjectAdapter modelOfClass:Post.class fromManagedObject:[[self fetchedResultsController] objectAtIndexPath:indexPath] error:nil];

The property comments on the post object is a empty NSSet, and I get quite some errors upon inserting the thing beforehand. The errors I get:

Core Data: annotation: repairing missing delete propagation for to-many relationship post_has_comments on object [...]

I am stuck - Maybe I am missing something huge here?

My Post Class implements the following static methods:

+ (NSDictionary *)managedObjectKeysByPropertyKey {
return @{
         @"post_id" : @"id",
         @"comments" : @"post_has_comments"
         };
}

+ (NSDictionary *)JSONKeyPathsByPropertyKey {
    return @{
             @"post_id" : @"id",
             };
}

+ (NSDictionary *)relationshipModelClassesByPropertyKey {
    return @{
             @"comments" : IHComment.class
             };
}

Answer 1

From the Mantle documentation:

Mantle makes it easy to write a simple model layer for your Cocoa or Cocoa Touch application.

This is simply an unproven statement. Looking at the framework, I do not see where the evidence is. You should get your objects, and insert them into Core Data using Apple's APIs.

Post *cdPost = [NSEntityDescription insertNewObjectForEntityForName:@"Post"
   inManagedObjectContext:self.managedObjectContext];
// configure the cdPost object with the data from the web service
for (id commentObject in commentArrayFromPostObject) {
   Comment *cdComment = 
       [NSEntityDescription insertNewObjectForEntityForName:@"Comment"
       inManagedObjectContext:self.managedObjectContext];
   // configure the cdComment object with the data from the web service
   cdComment.post = cdPost;
}

That's all there is to it.