gistfile1.m

NSEntityDescription *activityTypeEntity = [NSEntityDescription entityForName:@"ActivityType" inManagedObjectContext:managedObjectStore.persistentStoreManagedObjectContext];
NSRelationshipDescription *customerRelationship = [activityTypeEntity relationshipsByName][@"customer"];
RKConnectionDescription *connection = [[RKConnectionDescription alloc] initWithRelationship:customerRelationship attributes:@{ @"customerID": @"customerID" }];
[activityTypeMapping addConnection:connection];