iPhone RestKit 是否可以将核心数据对象图转换为 JSON？答案

【问题标题】：iPhone RestKit is it possible to convert a Core Data object graph into JSON?iPhone RestKit 是否可以将核心数据对象图转换为 JSON？
【发布时间】：2012-04-23 13:21:14
【问题描述】：

我正在为我的一个项目使用 RestKit 框架。它包括一个如何使用对象映射将 JSON 对象转换为核心数据图的示例。如果可能相反，我正在徘徊 - 可以将使用 RestKit 的核心数据实体转换回 JSON 表示形式吗？

我找到了 RKObjectSerializer 类，但我似乎无法让它工作 - 我得到的序列化对象是 nil

-(void)doCoreDataToJSONConversion
{
    Article* article = [_articles objectAtIndex:0];
    RKManagedObjectMapping* articleMapping = [RKManagedObjectMapping mappingForClass:[Article class]];
    NSAssert(articleMapping!=nil,@"article mapping is nil!");
    NSLog(@"%@",[article description]);

    RKObjectSerializer* serializer =[RKObjectSerializer serializerWithObject:article mapping:articleMapping];

    NSError* error = nil;
    NSMutableDictionary* serializedObject = [serializer serializedObject:&error];

    if(error!=nil)
    {
        NSLog(@"!!!!! Error: %@",[error localizedDescription]);
    }

    //prints nil
    NSLog(@"Serialized Object: %@", [serializedObject description]);
}

感谢您的意见！

【问题讨论】：

标签： iphone objective-c json core-data restkit

【解决方案1】：

无法准确地告诉您有关 RestKit 的信息，但您可以轻松地将所有核心数据图转换为 JSON 并返回，只要您看看 Marcus Zarra 的这个绝对精彩的答案

JSON and Core Data on the iPhone

【讨论】：

【解决方案2】：

我最终使用这些方法将核心数据对象转换为 JSON。要反序列化这些对象，我需要定义不同的映射类：RKManagedObjectMapping，它与常规对象映射略有不同。

-(void)setupObjectSerializationMapping
{
    RKObjectManager *objectManager = [RKObjectManager sharedManager ] ;
    RKObjectMapping *mapping = [RKObjectMapping mappingForClass:[Article class]];

    [mapping mapAttributes:@"articleID", @"title", @"body", nil];

    //********************************    

    RKObjectMapping *imageMapping = [RKObjectMapping mappingForClass:[EventImage class]];

    [imageMapping mapAttributes:@"createDate", @"localFilePath", nil];
    [objectManager.mappingProvider addObjectMapping:imageMapping];
    [objectManager.mappingProvider setSerializationMapping:[imageMapping inverseMapping] forClass:[EventImage class]];
    [objectManager.mappingProvider setMapping:imageMapping forKeyPath:@"eventImages"];

    //********************************    

    RKObjectMapping *eventMapping = [RKObjectMapping mappingForClass:[Event class]];

    [eventMapping mapAttributes:@"createDate", @"note", nil];
    [eventMapping mapRelationship:@"eventImages" withMapping:imageMapping];

    [objectManager.mappingProvider addObjectMapping:eventMapping];
    [objectManager.mappingProvider setSerializationMapping:[eventMapping inverseMapping] forClass:[Event class]];
    [objectManager.mappingProvider setMapping:eventMapping forKeyPath:@"events"];

    //******************************** 
    //setup App user mapping
    RKObjectMapping *userMapping = [RKObjectMapping mappingForClass:[AppUserSubclass class]];

    [userMapping mapAttributes:@"userID",@"firstName", @"lastName",@"localDataFilepath", nil];
    [userMapping mapRelationship:@"events" withMapping:eventMapping];
    [objectManager.mappingProvider addObjectMapping:userMapping];
    [objectManager.mappingProvider setSerializationMapping:[userMapping inverseMapping] forClass:[AppUserSubclass class]];
    [objectManager.mappingProvider setMapping:userMapping forKeyPath:@"appUser"];



}

-(NSString*)generateLocalJSONData
{

    NSString* folderPath = [self dataFolderPath];
    // remember what the file was called. This will not include the documents directory and will be the same on all machines.
    NSString* localFileName = [self fileName];

    NSString* dataFile = [self fullDocumentsFilePath];
    self.localDataFilepath = dataFile;

    NSAssert(self.localDataFilepath!=nil,@"failed to save local data path");
    //********************************


    NSError* error = nil;

    //app user subclass is the same as AppUser, but is used to differentiate between file based mapping and core data mapping
    RKObjectMapping *serMap = [[[RKObjectManager sharedManager] mappingProvider] serializationMappingForClass:[AppUserSubclass class]];
    NSDictionary *d = [[RKObjectSerializer serializerWithObject:self mapping:serMap] serializedObject:&error];


    if(error!=nil)
    {
        NSLog(@"!!!!! Error: %@",[error localizedDescription]);
    }


    NSString* dataContents = [d JSONString];
    BOOL success =  [dataContents writeToFile:dataFile atomically:YES encoding:NSUTF8StringEncoding error:nil];
    if(!success)
    {
        NSLog(@"Error writing to data file!");
    }
    [[AppUser managedObjectContext] save:nil];

    return dataFile;

}

【讨论】：