RestKit 嵌套关系

Question

使用 RestKit，我正在尝试映射以下 JSON。

{
  "userID": 1,
  "collections": [
    {
      "collectionID": 120,
      "friends": [
        {
          "friendID": 6,
          "orders": [
            {
              "orderID": 1,
              "name": "Small"
            }
          ]
        }
      ]
    },
    {
      "collectionID": 123,
      "friends": [
        {
          "friendID": 6,
          "orders": [
            {
              "orderID": 2,
              "name": "Medium"
            }
          ]
        }
      ]
    }
  ]
}

我正在使用 RestKit 和 MagicalRecord - 设置代码、映射和关系如下

NSURL *modelURL = [NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:@"Model" ofType:@"momd"]];
NSManagedObjectModel *managedObjectModel = [[[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL] mutableCopy];
RKManagedObjectStore *managedObjectStore = [[RKManagedObjectStore alloc] initWithManagedObjectModel:managedObjectModel];
NSString *storePath = [RKApplicationDataDirectory() stringByAppendingPathComponent:@"db.sqlite"];

[managedObjectStore addSQLitePersistentStoreAtPath:storePath fromSeedDatabaseAtPath:nil withConfiguration:nil options:nil error:nil];
[managedObjectStore createManagedObjectContexts];

// Configure MagicalRecord to use RestKit's Core Data stack
[NSPersistentStoreCoordinator MR_setDefaultStoreCoordinator:managedObjectStore.persistentStoreCoordinator];
[NSManagedObjectContext MR_setRootSavingContext:managedObjectStore.persistentStoreManagedObjectContext];
[NSManagedObjectContext MR_setDefaultContext:managedObjectStore.mainQueueManagedObjectContext];

RKObjectManager *objectManager = [RKObjectManager managerWithBaseURL:[NSURL URLWithString:@"http://127.0.0.1:3500"]];
objectManager.managedObjectStore = managedObjectStore;

RKEntityMapping *appMapping = [RKEntityMapping mappingForEntityForName:@"App" inManagedObjectStore:managedObjectStore];
appMapping.identificationAttributes = @[ @"userID" ];

RKEntityMapping *collectionMapping = [RKEntityMapping mappingForEntityForName:@"Collection" inManagedObjectStore:managedObjectStore];
collectionMapping.identificationAttributes = @[ @"collectionID" ];
[collectionMapping addAttributeMappingsFromArray:@[@"collectionID"]];

RKEntityMapping *friendMapping = [RKEntityMapping mappingForEntityForName:@"Friend" inManagedObjectStore:managedObjectStore];
friendMapping.identificationAttributes = @[ @"friendID" ];
[friendMapping addAttributeMappingsFromArray:@[@"friendID"]];

RKEntityMapping *orderMapping = [RKEntityMapping mappingForEntityForName:@"Order" inManagedObjectStore:managedObjectStore];
orderMapping.identificationAttributes = @[ @"orderID" ];
[orderMapping addAttributeMappingsFromArray:@[@"orderID", @"name"]];


RKRelationshipMapping *appCollectionRelationship = [RKRelationshipMapping relationshipMappingFromKeyPath:@"collections" toKeyPath:@"collections" withMapping:collectionMapping];
[appMapping addPropertyMapping:appCollectionRelationship];

RKRelationshipMapping *collectionFriendRelationship = [RKRelationshipMapping relationshipMappingFromKeyPath:@"friends" toKeyPath:@"friends" withMapping:friendMapping];
[collectionMapping addPropertyMapping:collectionFriendRelationship];

RKRelationshipMapping *friendsOrderRelationship = [RKRelationshipMapping relationshipMappingFromKeyPath:@"orders" toKeyPath:@"orders" withMapping:orderMapping];
[friendsOrderRelationship setAssignmentPolicy:RKUnionAssignmentPolicy];
[friendMapping addPropertyMapping:friendsOrderRelationship];

然后，使用下面的控制台查询我的 API 上的 /test 路由（输出上面的 JSON 块）...

RKResponseDescriptor *responseDescriptor = [RKResponseDescriptor responseDescriptorWithMapping:appMapping method:RKRequestMethodAny pathPattern:nil keyPath:nil statusCodes:RKStatusCodeIndexSetForClass(RKStatusCodeClassSuccessful)];
[objectManager addResponseDescriptor:responseDescriptor];

[objectManager getObjectsAtPath:@"/test" parameters:nil success:^(RKObjectRequestOperation *operation, RKMappingResult *mappingResult) {

    App *app = [mappingResult firstObject];
    for (Collection *collection in app.collections) {
        NSLog(@"collectionID = %@", collection.collectionID);
        for (Friend *friend in collection.friends) {
            NSLog(@"friendID = %@", friend.friendID);
            for (Order *order in friend.orders) {
                NSLog(@"Name = %@", order.name);
            }
        }
    }
} failure:^(RKObjectRequestOperation *operation, NSError *error) {}];

提供以下输出 - 注意两个名称都是中型，而不是一个小而另一个中型。

collectionID = 120
friendID = 6
Name = Medium
Name = Small
collectionID = 123
friendID = 6
Name = Medium
Name = Small

为什么会发生这种情况？我猜这是因为两个好友 ID 相同，即使他们在不同的收藏夹下...

Answer 1

这是因为您有identificationAttributes = @[ @"friendID" ]; 和关系的默认关系连接规则而不是替换。所以，第二个映射找到第一个映射创建的好友，替换订单关系内容。

您实际上无法根据您显示的 JSON 更改唯一标识符，但您可能需要检查它（根据您的对象图要求）。

另外/或者，请参阅this answer，了解如何更改关系分配策略以不丢失原始关系内容的详细信息。