使用 RestKIt 在核心数据实体中映射 json 对象

Question

我正在使用 RestKit 开发一些待办事项列表应用程序。我在iOS中使用CoreData返回的json表单服务器面临一些映射问题。

情景

以下是我正在使用的列表和任务实体的图像。

当有人向服务器上的列表添加新任务时，我返回该特定列表的以下 Json：

`GET www.mydomain.com\api\list\1`

        [ { "list" : 

          { "listID" : "1",
            "listName" : "New List ",
            "listSyncStatus" : "1"
          },
        "tasks" : [ { "listID" : "1",
              "taskCompletionStatus" : "1",
              "taskID" : "24",
              "taskName" : "Server Added 2",
              "taskSyncStatus" : "1"
            },
            { "listID" : "1",
              "taskCompletionStatus" : "1",
              "taskID" : "25",
              "taskName" : "Server Added 3",
              "taskSyncStatus" : "1"
            },
            { "listID" : "1",
              "taskCompletionStatus" : "1",
              "taskID" : "23",
              "taskName" : "Server Added",
              "taskSyncStatus" : "1"
            }
          ]
      } 
    ]

我对上述 json 的响应描述符如下：

    RKResponseDescriptor *taskResponseDescriptor = [RKResponseDescriptor responseDescriptorWithMapping:taskEntityMapping
                                                                                            method:RKRequestMethodGET
                                                                                       pathPattern:@"/api/list/:id"
                                                                                           keyPath:@"tasks"
                                                                                       statusCodes:RKStatusCodeIndexSetForClass(RKStatusCodeClassSuccessful)];

对于我的核心数据映射，我使用以下关系映射：

    [taskEntityMapping addPropertyMapping:[RKRelationshipMapping relationshipMappingFromKeyPath:@"list"
                                                                                  toKeyPath:@"list"
                                                                                withMapping:listEntityMapping]];

我的taskEntityMapping如下：

    NSDictionary *taskObjectMapping = @{
                                    @"listID" : @"listID",
                                    @"taskID" : @"taskID",
                                    @"taskName" : @"taskName",
                                    @"taskCompletionStatus" : @"taskCompletionStatus",
                                    @"taskSyncStatus" : @"taskSyncStatus"
                                };

RKEntityMapping *taskEntityMapping = [RKEntityMapping mappingForEntityForName:@"Task" inManagedObjectStore:managedObjectStore];
[taskEntityMapping addAttributeMappingsFromDictionary:taskObjectMapping];
taskEntityMapping.identificationAttributes = @[ @"taskID" ];

而我的listEntityMapping如下：

    //ALL LISTS RELATED REQUESTS
NSDictionary *listObjectMapping = @{
                                      @"listID" : @"listID",
                                      @"listName" : @"listName",
                                      @"listSyncStatus" : @"listSyncStatus",

                                  };

RKEntityMapping *listEntityMapping = [RKEntityMapping mappingForEntityForName:@"List" inManagedObjectStore:managedObjectStore];
[listEntityMapping addAttributeMappingsFromDictionary:listObjectMapping];

listEntityMapping.identificationAttributes = @[ @"listID" ];

在执行时，我的应用程序崩溃并出现以下错误 Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Expected a dictionary representation'

请求日志如下：

2014-02-03 13:17:29.789 RKGist[984:70b] T restkit.network:RKObjectRequestOperation.m:178 GET 'http://mydomain.com/api/list/1':
request.headers={
    Accept = "application/json";
    "Accept-Language" = "en;q=1, fr;q=0.9, de;q=0.8, zh-Hans;q=0.7, zh-Hant;q=0.6, ja;q=0.5";
    "User-Agent" = "RKGist/1.0 (iPhone Simulator; iOS 7.0.3; Scale/2.00)";
}
request.body=(null)
2014-02-03 13:17:30.670 RKGist[984:f03] T restkit.network:RKResponseMapperOperation.m:451 Mapping HTTP response to nil target object...
2014-02-03 13:17:30.670 RKGist[984:f03] D restkit.object_mapping:RKMapperOperation.m:377 Executing mapping operation for representation: (
        {
        list =         {
            listID = 1;
            listName = "New List ";
            listSyncStatus = 1;
        };
        tasks =         (
                        {
                listID = 1;
                taskCompletionStatus = 1;
                taskID = 24;
                taskName = "Server Added 2";
                taskSyncStatus = 1;
            },
                        {
                listID = 1;
                taskCompletionStatus = 1;
                taskID = 25;
                taskName = "Server Added 3";
                taskSyncStatus = 1;
            },
                        {
                listID = 1;
                taskCompletionStatus = 1;
                taskID = 23;
                taskName = "Server Added";
                taskSyncStatus = 1;
            }
        );
    }
)
 and targetObject: (null)
2014-02-03 13:17:30.671 RKGist[984:f03] T restkit.object_mapping:RKMapperOperation.m:320 Examining keyPath 'tasks' for mappable content...
2014-02-03 13:17:30.671 RKGist[984:f03] D restkit.object_mapping:RKMapperOperation.m:297 Found mappable collection at keyPath 'tasks': (
        (
                {
            listID = 1;
            taskCompletionStatus = 1;
            taskID = 24;
            taskName = "Server Added 2";
            taskSyncStatus = 1;
        },
                {
            listID = 1;
            taskCompletionStatus = 1;
            taskID = 25;
            taskName = "Server Added 3";
            taskSyncStatus = 1;
        },
                {
            listID = 1;
            taskCompletionStatus = 1;
            taskID = 23;
            taskName = "Server Added";
            taskSyncStatus = 1;
        }
    )
)

日志说在 keypath tasks 找到了可映射的集合。

谁能指导我在这里做错了什么。是我返回的 json 格式错误还是我的映射代码错误？

Answer 1

您的响应描述符使用keyPath:@"tasks"。这有效地“挖掘”了响应并忽略了tasks 部分之外的任何内容。这意味着在映射期间您无法访问list 部分。

将addPropertyMapping: 与关系一起用于嵌套映射 - 这不是您所拥有的。实际上，您有 2 个单独的部分需要单独映射（因此，2 个响应描述符）以创建具有关联 ID（以及连接对象的 ID）的所有对象。然后，您需要使用外键映射来建立连接（使用RKConnectionDescription）。

要检查的一件事是返回的 JSON 是什么。看起来好像它可能是 1 个包含对象的大型数组，这没有任何意义。如果它是一个数组，那么您将需要更改整个方法。它应该是 1 个带有多个键的对象...