RestKit 0.20 mapping string array - objective-c

Question

So after reading this answer, I do not see how my case is any different, but the proposed solution just doesn't seem to work in RestKit 0.20.3
For the following json:
{
"photos": [
"872ac577-3f31-47a0-966e-6f2ed2fbabcd"
],
"imageUrl": [
"http://domain/WebAPI/FileUpload/10232013629_21382571406.439790.jpeg"
]
}
Mapping into the following object:
#class Picture, Site, Survey;
#interface Job : NSManagedObject
#property (nonatomic, retain) NSString * jobId;
#property (nonatomic, retain) NSString * jobName;
#property (nonatomic, retain) NSString * jobStatusId;
#property (nonatomic, retain) NSString * jobStatus;
#property (nonatomic, retain) NSString * projectId;
#property (nonatomic, retain) NSString * projectType;
#property (nonatomic, retain) NSString * siteId;
#property (nonatomic, retain) NSSet *surveys;
#property (nonatomic, retain) NSSet *photos;
#property (nonatomic, retain) NSDate *createdDate;
#property (nonatomic, retain) Site *site;
#end
Where photos is a Picture object that looks like this:
#interface Picture : NSManagedObject
#property (nonatomic, retain) NSData * data;
#property (nonatomic, retain) NSString * photoId;
#property (nonatomic, retain) NSString * pictureLoc;
#property (nonatomic, retain) NSString * imageUrl;
#property (nonatomic, retain) Job *job;
#property (nonatomic, retain) QuestionAnswer *question;
#end
I want to map the photos and imageUrl into the Picture's photoId and imageUrl, respectively. I thought I could use the following in my Job's mapping:
RKEntityMapping *ret = [RKEntityMapping mappingForEntityForName:#"Job" inManagedObjectStore:[RKObjectManager sharedManager].managedObjectStore ];
[ret addAttributeMappingsFromDictionary: #{
#"photos": #"photos.photoId",
#"imageUrl": #"photos.imageUrl",
}];
However, the mapped Job always ends up with nothing in the photos property.
I know that I am doing all the in-between steps correctly (like actually using ret for the mapping), as the JSON is a snippet that contains many other keys I am able to map with no problem. What am I doing wrong? please tell me
EDIT
Changed the mapping code as per Wain's answer:
RKEntityMapping *ret = [RKEntityMapping mappingForEntityForName:#"Job" inManagedObjectStore:[RKObjectManager sharedManager].managedObjectStore ];
RKEntityMapping *subMapping = [RKEntityMapping mappingForEntityForName:#"Picture" inManagedObjectStore:[RKObjectManager sharedManager].managedObjectStore ];
[subMapping addAttributeMappingsFromDictionary: #{
#"photos":#"photoId",
#"imageUrl":#"imageUrl"
}];
[ret addPropertyMapping:[RKRelationshipMapping
relationshipMappingFromKeyPath:nil
toKeyPath:#"photos"
withMapping:subMapping]];
And now I get a Picture object added, but with nil for photoId and imageUrl (and yes, I checked to make sure I have the spelling and capitalization correct for the JSON keys)

Answer 1

The reason photos never has anything in it is that your mapping doesn't tell it to create a new object.
The problem is how you could tell it to create a single object and set both of the parameters into it. The problem is because you have 2 different arrays. The JSON I would expect you to have is 1 array which contains dictionaries with all of the details for that particular entry. RestKit can process both of the arrays but it would result in 2 distinct photo objects being created. To do this you need a second mapping with a nil key path and a relationship from ret to that new mapping.
An alternative could be to change the Job object so that it has 2 transformable (or transient) properties which are NSArrays. If you set ret to just map #"photos" : #"photos" and #"imageUrl" : #"imageUrl" then RestKit will map all of the data, just not into a photo object. You can then mutate this data after the mapping has completed if you want to...