RestKit 0.20 — CoreData：错误：无法调用 NSManagedObject 类上的指定初始化程序（再次）

Question

这个错误似乎已经出现过很多次了。这个问题最突出的答案似乎是 RestKit 0.20 — CoreData: error: Failed to call designated initializer on NSManagedObject class

但是，发布的解决方案对我不起作用。但是让我们从头开始：

我想将文件上传到服务器。我想解析响应以确保它已成功上传。如果没有，我稍后再试。为此，我的模型有一个名为 NSNumber *sentToServer 的布尔变量（在 CoreData 中，BOOL 保存为 NSNumber）。

因为我不知道发送是否会成功，所以我总是先将实体保存到我的 CoreData 模型中，然后再通过 RestKit 发送。

当 POST 请求成功时，服务器返回一个 JSON 字符串，如下所示：

{"id":14,"created":true}

请注意，当然，尚未在 CoreData 模型上设置 ID，因此 id 和 created 都是我的模型的新信息。

这是我的模型：

@interface Recording : NSManagedObject

@property (nonatomic, retain) NSString * audioFilePath;
@property (nonatomic, retain) NSDate * createdAt;
@property (nonatomic, retain) NSString * deviceId;
@property (nonatomic, retain) NSString * deviceType;
@property (nonatomic, retain) NSNumber * recordingId;
@property (nonatomic, retain) NSNumber * sentToServer;

@end

我是这样设置的：

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

NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
                         [NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption,
                         [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil];

if (![managedObjectStore addSQLitePersistentStoreAtPath:storePath
                                 fromSeedDatabaseAtPath: nil
                                      withConfiguration:nil
                                                options:options
                                                  error:&error]) {
    NSAssert(NO, @"Managed object store failed to create persistent store coordinator: %@", error);
}
[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];

NSString *databaseUrl = @"http://localhost:3000";
RKObjectManager *objectManager = [RKObjectManager managerWithBaseURL:[NSURL URLWithString:databaseUrl]];
objectManager.managedObjectStore = managedObjectStore;
objectManager.requestSerializationMIMEType = RKMIMETypeJSON;

// Setup mapping
RKEntityMapping* recordingRequestMapping = [RKEntityMapping mappingForEntityForName:@"Recording" inManagedObjectStore:managedObjectStore];
[recordingRequestMapping addAttributeMappingsFromDictionary:@{
 @"device_id": @"deviceId",
 @"device_type": @"deviceType"     }];

RKRequestDescriptor *requestDescriptor = [RKRequestDescriptor requestDescriptorWithMapping:[recordingRequestMapping inverseMapping]
                                                                               objectClass:[Recording class]
                                                                               rootKeyPath:@"recording"];
[objectManager addRequestDescriptor:requestDescriptor];

RKEntityMapping* recordingResponseMapping = [RKEntityMapping mappingForEntityForName:@"Recording" inManagedObjectStore:managedObjectStore];
[recordingResponseMapping addAttributeMappingsFromDictionary:@{
 @"created": @"sentToServer",
 @"id": @"recordingId"}];
recordingResponseMapping.identificationAttributes = @[@"recordingId"];

RKResponseDescriptor *responseDescriptor = [RKResponseDescriptor responseDescriptorWithMapping:recordingResponseMapping
                                                                                   pathPattern:@"/audio.json"
                                                                                       keyPath:nil
                                                                                   statusCodes:RKStatusCodeIndexSetForClass(RKStatusCodeClassSuccessful)];

[objectManager addResponseDescriptor:responseDescriptor];

首先，对于应该很常见的东西（只需初始化 RestKit 和 MagicalRecord），这是一个令人惊讶的冗长设置代码。但我离题了...

整个上传过程运行良好。请求映射很好，所有内容都存储在服务器上，包括附件。请注意，请求映射不包含文件，因为它们是通过多部分 post 方法发送的。同样，该部分工作正常。下面是上传文件的代码：

RKObjectManager *manager = [RKObjectManager sharedManager];
NSMutableURLRequest *request;

request = [manager multipartFormRequestWithObject:recording
                                           method:RKRequestMethodPOST
                                             path:@"audio.json" 
                                       parameters:nil
                        constructingBodyWithBlock:^(id<AFMultipartFormData> formData) {
        [formData appendPartWithFileData:[[NSFileManager defaultManager] contentsAtPath:recording.audioFilePath]
                                    name:@"recording[audio]"
                                fileName:[recording.audioFilePath lastPathComponent]
                                mimeType:@"audio/m4a"];
    }];

RKObjectRequestOperation *operation = [manager objectRequestOperationWithRequest:request
                                                                         success:^(RKObjectRequestOperation *op, RKMappingResult *mapping) {
                                                                             NSLog(@"successfully saved file on the server");
                                                                         }
                                                                         failure:^(RKObjectRequestOperation *op, NSError *error){
                                                                             NSLog(@"some weird error");
                                                                         }];


[manager enqueueObjectRequestOperation:operation];

将响应映射到对象变得很困难。如果没有匹配的响应映射，日志输出会包含无法处理响应的错误（惊喜）。 使用匹配的响应映射，但是，应用程序崩溃。这是堆栈跟踪：

#11 0x2f6482d6 in -[NSObject(NSKeyValueCoding) valueForKeyPath:] ()
#12 0x00113b9a in -[RKMappingOperation shouldSetValue:forKeyPath:usingMapping:] at /Users/earthnail/development/RestkitFileUpload/Pods/RestKit/Code/ObjectMapping/RKMappingOperation.m:436
#13 0x00114e40 in -[RKMappingOperation applyAttributeMapping:withValue:] at /Users/earthnail/development/RestkitFileUpload/Pods/RestKit/Code/ObjectMapping/RKMappingOperation.m:536
#14 0x00115fd4 in -[RKMappingOperation applyAttributeMappings:] at /Users/earthnail/development/RestkitFileUpload/Pods/RestKit/Code/ObjectMapping/RKMappingOperation.m:577
#15 0x0011c988 in -[RKMappingOperation main] at /Users/earthnail/development/RestkitFileUpload/Pods/RestKit/Code/ObjectMapping/RKMappingOperation.m:948
#16 0x2f655d0a in -[__NSOperationInternal _start:] ()
#17 0x0010cd5a in -[RKMapperOperation mapRepresentation:toObject:atKeyPath:usingMapping:metadata:] at /Users/earthnail/development/RestkitFileUpload/Pods/RestKit/Code/ObjectMapping/RKMapperOperation.m:256
#18 0x0010b6aa in -[RKMapperOperation mapRepresentation:atKeyPath:usingMapping:] at /Users/earthnail/development/RestkitFileUpload/Pods/RestKit/Code/ObjectMapping/RKMapperOperation.m:176
#19 0x0010ddc8 in -[RKMapperOperation mapRepresentationOrRepresentations:atKeyPath:usingMapping:] at /Users/earthnail/development/RestkitFileUpload/Pods/RestKit/Code/ObjectMapping/RKMapperOperation.m:314
#20 0x0010e552 in -[RKMapperOperation mapSourceRepresentationWithMappingsDictionary:] at /Users/earthnail/development/RestkitFileUpload/Pods/RestKit/Code/ObjectMapping/RKMapperOperation.m:359
#21 0x0010ee72 in -[RKMapperOperation main] at /Users/earthnail/development/RestkitFileUpload/Pods/RestKit/Code/ObjectMapping/RKMapperOperation.m:398
#22 0x2f655d0a in -[__NSOperationInternal _start:] ()
#23 0x00100e70 in -[RKObjectResponseMapperOperation performMappingWithObject:error:] at /Users/earthnail/development/RestkitFileUpload/Pods/RestKit/Code/Network/RKResponseMapperOperation.m:345
#24 0x000ff4e6 in -[RKResponseMapperOperation main] at /Users/earthnail/development/RestkitFileUpload/Pods/RestKit/Code/Network/RKResponseMapperOperation.m:297
#25 0x2f655d0a in -[__NSOperationInternal _start:] ()

调试器在[RKMappingOperation shouldSetValue:forKeyPath:usingMapping:] 中以SIGABRT 停止的行是：

id currentValue = [self.destinationObject valueForKeyPath:keyPath];

请注意，当我按照https://stackoverflow.com/a/13734348/487556 中的建议设置断点时，永远不会到达该断点。这意味着响应映射的路径没有问题。

我可以想象这里有几件事会出错：

1. RestKit 假设还没有 CoreData 实体并想要创建一个。这会导致重复的实体（这会很糟糕！），但它仍然不应该崩溃，因为模型的所有字段都是可选。
2. RestKit 尝试根据 ID 查找 CoreData 实体（因为这是标识符变量），但当然 ID 尚未设置。
3. 别的东西...

有什么建议吗？

Answer 1

我知道你已经有一段时间没有问过了，也许你已经找到了自己的方式，但我只是遇到了同样的情况并找到了解决方案。

问题在于您在使用 NSManagedObjects 时使用了objectRequestOperationWithRequest:success:failure: 方法。因此，RestKit 在映射操作过程中尝试实例化一个常规的 NSObject，从而导致崩溃。

尝试改用managedObjectRequestOperationWithRequest:managedObjectContext:success:failure:，情况应该会更好。

Answer 2

问题在于响应描述和请求中的匹配路径。为了使它起作用，它们中的斜线应该是相同的，@"/audio.json" 或 @"audio.json" 否则 RestKit 看不到一个匹配另一个。