“找不到给定内容的任何映射，keyPath=null”RestKit 0.2

Question

所以我转而使用 RestKit 0.2 和 CoreData，但在尝试正确映射时遇到了很多麻烦……我不明白为什么。我的服务器的 JSON 响应是这样的：

{
"meta": 
   {
   "limit": 20, 
   "next": null, 
   "offset": 0, 
   "previous": null, 
   "total_count": 2
   }, 
   "objects": 
   [{
       "creation_date": "2012-10-15T20:16:47", 
       "description": "", 
       "id": 1, 
       "last_modified": 
       "2012-10-15T20:16:47", 
       "order": 1, 
       "other_names": "", 
       "primary_name": "Mixing",
       "production_line": "/api/rest/productionlines/1/", 
       "resource_uri": "/api/rest/cells/1/"
   }, 
   {
       "creation_date": "2012-10-15T20:16:47", 
       "description": "",
       "id": 2, 
       "last_modified": "2012-10-15T20:16:47",
       "order": 2, "other_names": "", 
       "primary_name": "Packaging", 
       "production_line": "/api/rest/productionlines/1/",
       "resource_uri": "/api/rest/cells/2/"
   }]
}

然后在 XCode 中我有：

RKObjectManager *objectManager = [RKObjectManager sharedManager];

[AFNetworkActivityIndicatorManager sharedManager].enabled = YES;

NSManagedObjectModel *managedObjectModel = [NSManagedObjectModel mergedModelFromBundles:nil];
RKManagedObjectStore *managedObjectStore = [[RKManagedObjectStore alloc] initWithManagedObjectModel:managedObjectModel];
objectManager.managedObjectStore = managedObjectStore;


RKEntityMapping *cellMapping = [RKEntityMapping mappingForEntityForName:@"Cell" inManagedObjectStore:managedObjectStore];
cellMapping.primaryKeyAttribute = @"identifier";
[cellMapping addAttributeMappingsFromDictionary:@{
 @"id": @"identifier",
 @"primary_name": @"primaryName",
 }];



RKResponseDescriptor *responseCell = [RKResponseDescriptor responseDescriptorWithMapping:cellMapping
                                                                             pathPattern:@"/api/rest/cells/?format=json"
                                                                                 keyPath:@"objects"
                                                                             statusCodes:RKStatusCodeIndexSetForClass(RKStatusCodeClassSuccessful)];


[objectManager addResponseDescriptorsFromArray:@[responseCell, responseUser, responseCompany]];


[managedObjectStore createPersistentStoreCoordinator];
NSString *storePath = [RKApplicationDataDirectory() stringByAppendingPathComponent:@"AppDB.sqlite"];
NSString *seedPath = [[NSBundle mainBundle] pathForResource:@"SeedDatabase" ofType:@"sqlite"];
NSError *error;
NSPersistentStore *persistentStore = [managedObjectStore addSQLitePersistentStoreAtPath:storePath fromSeedDatabaseAtPath:seedPath withConfiguration:nil options:nil error:&error];
NSAssert(persistentStore, @"Failed to add persistent store with error: %@", error);

// Create the managed object contexts
[managedObjectStore createManagedObjectContexts];

// Configure a managed object cache to ensure we do not create duplicate objects
managedObjectStore.managedObjectCache = [[RKInMemoryManagedObjectCache alloc] initWithManagedObjectContext:managedObjectStore.persistentStoreManagedObjectContext];

我的要求是：

    [[RKObjectManager sharedManager] getObjectsAtPath:@"/api/rest/cells/?format=json" parameters:nil success:^(RKObjectRequestOperation *operation, RKMappingResult *mappingResult) {
        RKLogInfo(@"Load complete: Table should refresh...");

        [[NSUserDefaults standardUserDefaults] setObject:[NSDate date] forKey:@"LastUpdatedAt"];
        [[NSUserDefaults standardUserDefaults] synchronize];
    } failure:^(RKObjectRequestOperation *operation, NSError *error) {
        RKLogError(@"Load failed with error: %@", error);
    }];

而且我总是收到以下错误：

**Error Domain=org.restkit.RestKit.ErrorDomain Code=1001 "Unable to find any mappings for the given content" UserInfo=0x1102d500 {DetailedErrors=(), NSLocalizedDescription=Unable to find any mappings for the given content, keyPath=null}**

非常感谢！

更新：我添加了 cellMapping.forceCollectionMapping = YES; 但仍然没有运气:(！

更新 #2：按照 Blake 的建议，我尝试更改路径并且成功了！我做了 /api/rest/cells/ 而不是 /api/rest/cells/?format=json 并且我的服务器返回了所有内容并且映射成功！

现在我得到的唯一问题是以下错误：

2012-11-21 14:48:49.414 App[3125:617] W restkit.object_mapping:RKMapperOperation.m:176 强制集合映射但可映射对象的类型为“__NSCFArray”而不是 NSDictionary

Answer 1

听起来响应描述符与请求的 URL 不匹配。两个想法：

1. 尝试完全删除路径模式（传入 nil）并仅在“单元格”上使用基于键路径的匹配
2. 尝试使用“/api/rest/cells”的路径模式

接下来我会尝试使用调试器来逐步完成匹配。在RKObjectManager 中，候选响应映射列表由RKFilteredArrayOfResponseDescriptorsMatchingPath 函数构建。如果那里没有返回您预期的响应映射，则路径模式的请求路径无法评估。

如果那里看起来不错，下一个可能发生不匹配的地方是RKResponseMapperOperation 中的buildResponseMappingsDictionary 方法。此方法根据每个响应描述符评估响应。如果响应未能与您的响应描述符匹配，那么您将在这里得到意想不到的结果。

最后检查的地方是 RKResponseMapperOperation。这从匹配的描述符中获取映射并应用它们。 RKMapperOperation main 方法应该包含您期望的反序列化响应和mappingsDictionary 属性上的适当映射。

Answer 2

即使设置看起来正确，映射也是错误的。您的映射调用的信息嵌套在给定的对象中，因此您必须告诉映射查找对象内部的值。

RKEntityMapping *cellMapping = [RKEntityMapping mappingForEntityForName:@"Cell" inManagedObjectStore:managedObjectStore];
cellMapping.primaryKeyAttribute = @"identifier";

[cellMapping mapKeyOfNestedDictionaryToAttribute:@"objects"];
[cellMapping mapFromKeyPath:@".id" toAttribute:"identifier"];
[cellMapping mapFromKeyPath:@"primary_name" toAttribute:"primaryName"];

更多信息请查看RKObjectMapping Reference。