iOS - Reskit: deleting orphaned objects - ios

Question

I'm having an issue with ResKit for managing orphaned objects when, the JSON received from the same webService, must be mapped in multiple entities.
I've followed the example here http://restkit.org/api/latest/Classes/RKManagedObjectRequestOperation.html (under section "Deleting orphaned objects") and I can get orphaned objects deleted, but only for a single entity.
Let's see some code...
What follow is a (small part) JSON that I receive from webService.
{
"families": [
{
"id": "000",
"desc": "desc_1"
},
{
"id": "001",
"desc": "desc_2"
}
],
"categories": [
{
"id": "00000000",
"desc": "test"
....//others attributes
},
{
"id": "00000001",
"desc": "test"
....//others attributes
}
]
}
I'm mapping this JSON correctly to 2 different entities: Category and Family.
Now, for what I've understand, I can delete orphaned objects (objects no more received from server) by adding a FetchRequestBlock to my RKObjectManager.
Here is how I define it:
[objectManager addFetchRequestBlock:^NSFetchRequest *(NSURL *URL) {
RKPathMatcher* pathMatcher = [RKPathMatcher pathMatcherWithPattern:#"getData.asp"];
NSDictionary *dic = nil;
if ([pathMatcher matchesPath:[URL relativePath] tokenizeQueryStrings:YES parsedArguments:&dic]) {
NSFetchRequest *fetchRequest = [NSFetchRequest new];
NSEntityDescription *entity = [NSEntityDescription
entityForName:#"Family" inManagedObjectContext: managedObjectStore.mainQueueManagedObjectContext];
fetchRequest.entity = entity;
return fetchRequest;
} else
return nil;
}];
My questions: as you can see, in the FetchRequestBlock, I'm defining only the entity "Family", but I want to delete orphaned objects of "Category" entity inside the same block...is this possible ? Or I have to create another similar block that differs only for the entity name ?
And is there a method to add a "keyPath" (like "categories" or "families" in this example) to the FetchRequestBlock so I can be sure to delete the correct NSManagedObject? Or is this unnecessary?
EDIT:
For completion I add some more code, so I think you can understand better what I'm doing (and, in case, correct me if I'm doing something wrong...)
Here is how I define RKResponseDescriptor, where I can correctly associate it to a "KeyPath":
//Categories
RKResponseDescriptor *categoriesDescriptor = [RKResponseDescriptor responseDescriptorWithMapping:categoriesMapping
method:RKRequestMethodGET
pathPattern:#"getData.asp" keyPath:#"categories"
statusCodes:RKStatusCodeIndexSetForClass(RKStatusCodeClassSuccessful)];
//Families
RKResponseDescriptor *familiesDescriptor = [RKResponseDescriptor responseDescriptorWithMapping:familiesMapping
method:RKRequestMethodGET
pathPattern:#"getData.asp" keyPath:#"families"
statusCodes:RKStatusCodeIndexSetForClass(RKStatusCodeClassSuccessful)];
And I retrieve data from webService using the following code:
[[RKObjectManager sharedManager] getObjectsAtPath:#"getData.asp" parameters:#{kAuthKeyName : kAuthKeyValue} success:^(RKObjectRequestOperation *operation, RKMappingResult *mappingResult) {
//Success block
//Before entering in this block, I can see with debug that ResKit try to
//automatically delete objects that return from the "FetchRequestBlock" defined in above code...
}failure:^(RKObjectRequestOperation *operation, NSError *error) {
//Failure Block
}];