Mapping nested object with RESTKIT - ios

Question

I'm trying to map a object through the following JSON:
{
"main_email": {"id": 1, "address": "mainemail#email.com"},
"id": 1,
"first_name": "first name",
"last_name": "last name",
}
I have a object called User with the properties:
#property (nonatomic, assign) NSInteger userID;
#property (nonatomic, copy) NSString *firstName;
#property (nonatomic, copy) NSString *lastName;
#property (nonatomic, strong) Email *mainEmail;
And the object Email have the properties:
#property (nonatomic, assign) NSInteger emailID;
#property (nonatomic, copy) NSString *emailAddress;
Now i'm mapping in the User like bellow:
RKObjectMapping *userMapping = [RKObjectMapping mappingForClass:[User class]];
[userMapping addAttributeMappingsFromDictionary:#{#"id": #"userID",
#"first_name": #"firstName",
#"last_name": #"lastName"}];
RKObjectMapping *emailMapping = [RKObjectMapping mappingForClass:[Email class]];
[emailMapping addAttributeMappingsFromDictionary:#{#"main_email.id": #"emailID",
#"main_email.address": #"emailAddress"}];
[userMapping addPropertyMapping:[RKRelationshipMapping relationshipMappingFromKeyPath:#"mainEmail"
toKeyPath:#"mainEmail"
withMapping:emailMapping]];
This code keeps returning a empty Email object in User.mainEmail

Answer 1

First off your property mapping should be fromKeyPath:#"main_email" toKeyPath:#"mainEmail" the fromKeyPath is the key path in the JSON and the toKeyPath is the attribute/relationship in CoreData.
Second in your email mapping you don't need to prefix each key path with "main_email." when RestKit does nested mapping it will handle this for you (assuming your property mapping is set up properly)
Here is your example with those changes:
RKObjectMapping *userMapping = [RKObjectMapping mappingForClass:[User class];
[userMapping addAttributeMappingsFromDictionary:#{#"id": #"userID",
#"first_name": #"firstName",
#"last_name": #"lastName"}];
RKObjectMapping *emailMapping = [RKObjectMapping mappingForClass:[Email class]];
[emailMapping addAttributeMappingsFromDictionary:#{#"id": #"emailID",
#"address": #"emailAddress"}];
[userMapping addPropertyMapping:[RKRelationshipMapping relationshipMappingFromKeyPath:#"main_email"
toKeyPath:#"mainEmail"
withMapping:emailMapping]];