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我正在尝试通过 RestKit 将用户和组映射到 CoreData 对象，保持两者之间的关系。

用户的 JSON 类似于

{"users":
  [{"fullname": "John Doe", "_id": "1"}
   ...
  ]
}

组的 JSON 类似于

{"groups":
  [{"name": "John's group", "_id": "a",
    "members": ["1", "2"]
   ...
  ]
}

我也有相应的 Core Data 对象，User并且Group，在组和用户之间具有一对多的关系映射。中的关系属性Group被调用members，一个单独的NSArray被调用memberIDs保存所有成员用户的字符串 ID 数组。

我想在 RestKit 中完成的是加载这些对象并为我映射关系。加载用户的代码是直接的标准东西，加载组的代码类似于

RKObjectManager* objectManager = [RKObjectManager sharedManager];
RKManagedObjectMapping* groupMapping = [RKManagedObjectMapping mappingForClass:[Group class] inManagedObjectStore:objectManager.objectStore];
groupMapping.primaryKeyAttribute = @"identifier";
[groupMapping mapKeyPath:@"_id" toAttribute:@"identifier"];
[groupMapping mapKeyPath:@"name" toAttribute:@"name"];
[groupMapping mapKeyPath:@"members" toAttribute:@"memberIDs"];
[objectManager.mappingProvider setMapping:groupMapping forKeyPath:@"groups"];

// Create an empty user mapping to handle the relationship mapping
RKManagedObjectMapping* userMapping = [RKManagedObjectMapping mappingForClass:[User class] inManagedObjectStore:objectManager.objectStore];

[groupMapping hasMany:@"members" withMapping:userMapping];
[groupMapping connectRelationship:@"members" withObjectForPrimaryKeyAttribute:@"memberIDs"];

RKObjectRouter* router = objectManager.router;

[router routeClass:[Group class] toResourcePath:@"/rest/groups/:identifier"];
[router routeClass:[Group class] toResourcePath:@"/rest/groups/" forMethod:RKRequestMethodPOST];
// Assume url is properly defined to point to the right path...
[[RKObjectManager sharedManager] loadObjectsAtResourcePath:url usingBlock:^(RKObjectLoader *loader) {}];

当我运行此代码时，我多次收到以下警告（似乎每个关系大约两次）：

2012-10-24 08:55:10.170 Test[35023:18503] W restkit.core_data.cache:RKEntityByAttributeCache.m:205 Unable to add object with nil value for attribute 'identifier': <User: 0x86f7fc0> (entity: User; id: 0x8652400 <x-coredata:///User/t01A9EDBD-A523-4806-AFC2-9B06873D764E531> ; data: {
    fullname = nil;
    identifier = nil;
})

奇怪的是，关系设置正确（甚至查看了 sqlite 数据库，那里的一切看起来都很好）但我对 RestKit 代码中明显出错的地方不满意，它似乎与我在上面的代码中创建的虚假用户映射（它是空的，因为在 ID 数组中没有要映射的内容）。

我尝试了替代方案，例如当我添加键路径映射时：

[userMapping mapKeyPath:@"" toAttribute:@"identifier"];

它抱怨，显然是因为关键路径是空的

2012-10-24 09:24:11.735 Test[35399:14003] !! Uncaught exception !!
[<__NSCFString 0xa57f460> valueForUndefinedKey:]: this class is not key value coding-compliant for the key .

如果我尝试使用真实的User映射

[groupMapping hasMany:@"members" withMapping:[[RKObjectManager sharedManager].mappingProvider objectMappingForKeyPath:@"users"]];

我收到以下错误

2012-10-24 09:52:49.973 Test[35799:18403] !! Uncaught exception !!
[<__NSCFString 0xa56e9a0> valueForUndefinedKey:]: this class is not key value coding-compliant for the key _id.
2012-10-24 09:52:49.973 Test[35799:18403] *** Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[<__NSCFString 0xa56e9a0> valueForUndefinedKey:]: this class is not key value coding-compliant for the key _id.'

似乎 RestKit 正在尝试将 memberIDs 数组中的 ID 字符串本身映射到User对象，这没有任何意义。我见过一些例子，其中关系数组是一个带有键（例如称为id）的字典列表，其中包含另一个对象的引用 ID，例如：

{"groups":
  [{"name": "John's group", "_id": "a",
    "members": [
      {"_id": "1"},
      {"_id": "2"}
     ]
   ...
  ]
}

但我不想以这种方式更改我的 JSON（此外，我希望 RestKit 足够灵活以支持另一种方式。）

有谁知道在 RestKit 中进行这种关系映射的正确方法是什么？

更新

我最终修改了 REST 接口以发送包含用户对象 ID 的字典列表（就像上面的最后一个示例一样），并让它工作。仍然对设置不完全满意，但代码现在看起来像

RKObjectManager* objectManager = [RKObjectManager sharedManager];
RKManagedObjectMapping* groupMapping = [RKManagedObjectMapping mappingForClass:[Group class] inManagedObjectStore:objectManager.objectStore];
groupMapping.primaryKeyAttribute = @"identifier";
[groupMapping mapKeyPath:@"_id" toAttribute:@"identifier"];
[groupMapping mapKeyPath:@"name" toAttribute:@"name"];
[groupMapping mapKeyPath:@"members._id" toAttribute:@"memberIDs"];
[objectManager.mappingProvider setMapping:groupMapping forKeyPath:@"groups"];

// Create an empty user mapping to handle the relationship mapping
RKManagedObjectMapping* userMapping = [RKManagedObjectMapping mappingForClass:[User class] inManagedObjectStore:objectManager.objectStore];
userMapping.primaryKeyAttribute = @"identifier";
[userMapping mapKeyPath:@"_id" toAttribute:@"identifier"];

[groupMapping hasMany:@"members" withMapping:userMapping];
[groupMapping connectRelationship:@"members" withObjectForPrimaryKeyAttribute:@"memberIDs"];

RKObjectRouter* router = objectManager.router;

[router routeClass:[Group class] toResourcePath:@"/rest/groups/:identifier"];
[router routeClass:[Group class] toResourcePath:@"/rest/groups/" forMethod:RKRequestMethodPOST];
// Assume url is properly defined to point to the right path...
[[RKObjectManager sharedManager] loadObjectsAtResourcePath:url usingBlock:^(RKObjectLoader *loader) {}];

以防万一这对处于类似情况的其他人有所帮助。我采用的方法可能仍然存在一些问题，但到目前为止一切都很好（它甚至可以处理乱序加载，这很好） - 如果我的原始问题有答案，我仍然很乐意听取任何人的意见。

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1 回答 1

2

找到了一种方法来完成这项工作，并且还意识到我的问题中的更新方法只应该用于嵌套对象，而不是引用对象。这个线程让我走上了正确的轨道：https : //groups.google.com/forum/#!msg/restkit/swB1Akv2lT​​E/mnP2OMSqElwJ（如果你正在处理 RestKit 中的关系，值得一读）

假设 JSON 组仍然看​​起来像原始 JSON：

{"groups":
  [{"name": "John's group", "_id": "a",
    "members": ["1", "2"]
   ...
  ]
}

还假设用户被映射到一个键路径users（即类似的东西[objectManager.mappingProvider setMapping:userMapping forKeyPath:@"users"];）映射关系的正确方法如下所示：

RKObjectManager* objectManager = [RKObjectManager sharedManager];
RKManagedObjectMapping* groupMapping = [RKManagedObjectMapping mappingForClass:[Group class] inManagedObjectStore:objectManager.objectStore];
groupMapping.primaryKeyAttribute = @"identifier";
[groupMapping mapKeyPath:@"_id" toAttribute:@"identifier"];
[groupMapping mapKeyPath:@"name" toAttribute:@"name"];
[groupMapping mapKeyPath:@"members" toAttribute:@"memberIDs"];
[objectManager.mappingProvider setMapping:groupMapping forKeyPath:@"groups"];

[groupMapping mapKeyPath:@"users" toRelationship:@"members" withMapping:[[RKObjectManager sharedManager].mappingProvider objectMappingForKeyPath:@"users"] serialize:NO];
[groupMapping connectRelationship:@"members" withObjectForPrimaryKeyAttribute:@"memberIDs"];

RKObjectRouter* router = objectManager.router;
[router routeClass:[Group class] toResourcePath:@"/rest/groups/:identifier"];
[router routeClass:[Group class] toResourcePath:@"/rest/groups/" forMethod:RKRequestMethodPOST];
// Assume url is properly defined to point to the right path...
[[RKObjectManager sharedManager] loadObjectsAtResourcePath:url usingBlock:^(RKObjectLoader *loader) {}];

当我之前尝试过这种方法时，让我感到困惑的是这条线

[groupMapping mapKeyPath:@"users" toRelationship:@"members" withMapping:[[RKObjectManager sharedManager].mappingProvider objectMappingForKeyPath:@"users"] serialize:NO];

其中第一个键路径是指被引用对象的键路径映射（users在这种情况下），而不是group被映射对象内关系的键路径（members在这种情况下）。

随着这一变化，所有关系都按预期工作，我很高兴。

于 2012-10-27T20:13:17.010 回答