RestKit - Hydrate array of foreign keys - objective-c

Question

I have the following JSON:
{
"users": [
{"id": "1", "name": "John Doe"},
{"id": "2", "name": "Bill Nye"}
],
"groups": [
{"id": "1", "name": "Group1", "users": ["1", "2"]},
{"id": "2", "name": "Group2", "users": ["1"]}
]
}
...and a Core Data model with User and Group objects. The group object has a to-many relationship (NSSet) to users.
I have found the following thread that seems to indicate that this is possible, but contains no explanation of how such a mapping is to be performed:
https://github.com/RestKit/RestKit/issues/284
How do I perform this mapping such that each Group's "users" relationship is properly connected?
Note: I have mappings set up that correctly map the JSON users and groups to their respective Core Data objects. However, each group's "users" NSSet is empty.

Answer 1

So, I figured this out using RestKit 0.20(pre2).
JSON needed to be changed to the following (note the attribute names in the group's users array):
{
"users": [
{"id": "1", "name": "John Doe"},
{"id": "2", "name": "Bill Nye"}
],
"groups": [
{"id": "1", "name": "Group1", "users": [{"id" : "1"}, {"id" : "2"}]},
{"id": "2", "name": "Group2", "users": [{"id" : "1"}]}
]
}
Then, the following mappings:
RKEntityMapping *userMapping = [RKEntityMapping mappingForEntityForName:#"User" inManagedObjectStore:managedObjectStore];
userMapping.identificationAttributes = #[#"id"];
[userMapping addAttributeMappingsFromArray:#[#"id", #"name"]];
RKEntityMapping *groupMapping = [RKEntityMapping mappingForEntityForName:#"Group" inManagedObjectStore:managedObjectStore];
groupMapping.identificationAttributes = #[#"id"];
[groupMapping addAttributeMappingsFromArray:#[#"id", #"name"]];
[groupMapping addRelationshipMappingWithSourceKeyPath:#"users" mapping:userMapping];
And finally, the following responseDescriptors:
RKResponseDescriptor *userResponseDescriptor = [RKResponseDescriptor responseDescriptorWithMapping:classMapping pathPattern:#"/api/allthejson" keyPath:#"users" statusCodes:RKStatusCodeIndexSetForClass(RKStatusCodeClassSuccessful)];
RKResponseDescriptor *groupResponseDescriptor = [RKResponseDescriptor responseDescriptorWithMapping:classMapping pathPattern:#"/api/allthejson" keyPath:#"groups" statusCodes:RKStatusCodeIndexSetForClass(RKStatusCodeClassSuccessful)];
[objectManager addResponseDescriptorsArray:#[userResponseDescriptor, groupResponseDescriptor]];
Then get your objects using RKObjectManager's getObjectsAtPath:parameters:success:failure method and your done!

Answer 2

RestKit has many issues especially when it comes to modeling relationships. Debugging the mappings can be daunting.
Here is some code that deals with what you describe without RestKit.
NSArray *userArray;
// an array populated with NSManagedObjects
// correctly converted from JSON to the User entity
NSArray *groups = [jsonObject objectForKey:#"groups"];
for (NSDictionary *d in groups) {
Group *g = [NSEntityDescription insertNewObjectForEntityForName:#"Group"
inManagedObjectContext:_managedObjectContext];
g.id = #([d[#"id"] intValue]);
g.name = d[#"name"];
NSArray *users = d[#"users"];
for (NSString *s in users) {
User *u = [[userArray filteredArrayUsingPredicate:
[NSPredicate predicateWithFormat:#"id = %#", #([s intValue])]]
objectAtIndex:0];
[g addUsersObject:u];
}
}
// save