iPhone RestKit是否可以将Core Data对象图转换为JSON？

Question

我正在为我的一个项目使用RestKit框架。 它包含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。 如果可能的话，我会徘徊 - 使用RestKit的Core Data实体是否可以转换回JSON表示？

我找到了RKObjectSerializer类，但我似乎无法使它工作 - 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]);
}

谢谢您的意见！

Answer 1

无法准确地告诉您有关RestKit的信息，但是如果您只是看看Marcus Zarra的这个绝对精彩的答案，您可以轻松地将所有Core Data图表转换为JSON并返回

iPhone上的JSON和核心数据

Answer 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，我需要定义一个不同的映射类：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;

}