Connecting Non-Nested Relationships Using Foreign Keys

[Beniamiiin]

Hello.

FastEasyMapping support non-nested relationships using foreign keys like RestKit?

Connecting Non-Nested Relationships Using Foreign Keys

JSON attributes are sometimes foreign key identifiers to existing Core Data entities, such as entities obtained by a separate RKObjectRequestOperation. RestKit provides a method to map to an entity
using a foreign key identifier. Consider the following JSON:

{ "cities": [
      { "cityID": 1, "cityName": "Chicago" },
      { "cityID": 2, "cityName": "New York" }],
  "users": [
      { "userID":101, "userName": "Jeff", "cityID": 1 },
      { "userID":102, "userName": "Mary", "cityID": 2 },
      { "userID":103, "userName": "Sam",  "cityID": 1 }]
}

and the corresponding models where User has a Core Data relationship to City:

@interface City: NSManagedObject
    @property (nonatomic, retain) NSNumber* cityID;
    @property (nonatomic, retain) NSString* cityName;
@end

@interface User: NSManagedObject
    @property (nonatomic, retain) NSNumber* userID;
    @property (nonatomic, retain) NSString* userName;
    @property (nonatomic, retain) NSNumber* cityID;
    @property (nonatomic, retain) City* city;
@end

To connect the User entity to the City entity referenced by cityID property, you do the following after creating the RKEntityMapping for the User:

[userMapping addConnectionForRelationship:@"city" connectedBy:@{@"cityID": @"cityID"}];

The relationship value @"city" specifies the relationship object or name of the relationship object that is to be connected. The connectedBy: parameter is an NSDictionary mapping the User attribute to the City attribute. Since the attribute names are identical, the connectedBy: parameter can be also specified by an NSString, i.e. @"cityID".

[dimazen]

Hello, @BenjaminSarkisyan
In short: yes, it is possible.
All you need to do is: add relationship to the entity mapping. In entity mapping you should have only one Attribute Mapping for PK property and no key path.

[Beniamiiin]

@dimazen Thank you for your reply, but can you write example please.

[dimazen]

Sure:

FEMManagedObjectMapping *userMapping = [FEMManagedObjectMapping mappingForEntityName:@"User"];
[userMapping setPrimaryKey:@"userID"];
[userMapping addAttributeWithProperty:@"userID" keyPath:@"userID"];

FEMManagedObjectMapping *cityMapping = [FEMManagedObjectMapping mappingForEntityName:@"City"];
[cityMapping setPrimaryKey:@"cityID"];
[cityMapping addAttributeWithProperty:@"cityID" keyPath:nil];

[userMapping addRelationshipMapping:cityMapping forProperty:@"city" keyPath:@"cityID"];

[Beniamiiin]

Thank you very much.