Map a Objects to list of key/value

Question

I have a list of objects, which I would like to map to json as following:

"tags": {
    "f6a34fea-5d06-4fb2-a2c7-127e2b58165a": true,
    "39413ca6-b817-4ede-abd3-35822aec91b6": true
  },

What I currently have:

RKObjectMapping *tagRequestMapping = [RKObjectMapping mappingForClass:[NSMutableDictionary class]];
[tagRequestMapping addAttributeMappingToKeyOfRepresentationFromAttribute:@"id"];
[tagRequestMapping addAttributeMappingsFromDictionary:@{@"hasTasks" : @"(id)"}];
tagRequestMapping.forceCollectionMapping = NO;
[taskRequestMapping addPropertyMapping:[RKRelationshipMapping relationshipMappingFromKeyPath:@"tags"
                                                                                   toKeyPath:@"tags"
                                                                                 withMapping:tagRequestMapping]];

This results in the following json:

"tags": [
    {
      "f6a34fea-5d06-4fb2-a2c7-127e2b58165a": true
    },
    {
      "39413ca6-b817-4ede-abd3-35822aec91b6": true
    }
  ],

Unfortunately the webapp does not accept this as valid. I use the same rules to map the data from json to my core data objects, where it works just fine. But not for Core Data to json. How would I have to modify my mapping, to get one single object with all the values, just as specified?

Answer 1

Thanks to Wain I came up with a solution:

I added a new property to my Task class, that is readonly and has a custom getter. In that getter I create a dictionary from my NSSet of Tag objects. Then for the mapping part, I just added my new property as a normal attribute that should be mapped and it worked perfectly.

Custom Getter:

- (NSDictionary *)getTagDictionary {
    NSMutableDictionary *tagDictionary = [NSMutableDictionary dictionary];
    for (Tag *tag in self.tags) {
        [tagDictionary setObject:tag.hasTasks forKey:tag.id];
    }
    return tagDictionary;
}

Mapping:

[taskRequestMapping addAttributeMappingsFromDictionary:@{
        @"tagDictionary":@"tags"}];