RestKit：连接不在响应中的关系

Question

假设在我的数据模型中，我有Pages，其中有许多Comments。

我想连接模型中的一个关系，该关系从Comment返回到它所属的Page，但Page对象不嵌套在响应中，也没有任何可以标识父页面的主键出现在回复中。

当我拨打loadObjectsAtResourcePath时，加载的所有Comments都应该属于固定的已知Page对象。我可以挂钩的关系的一种方式是做：

loader.onDidLoadObjects = ^(NSArray* objs) { 
    for (Comment* comment in objs) comment.page = self.page; 
    ... 
} 

但我希望有一个更好的办法。请注意，我不能使用connectRelationship系列方法，因为响应中没有主键，可以让我将每个Comment都挂钩到Page。

Answer 1

您可以使用委托方法- (void)objectLoader:(RKObjectLoader *)loader willMapData:(inout id *)mappableData在映射步骤之前注入额外的参数。它确保在使用核心数据时，RestKit可以正确保存对象和关系（请注意，上面给出的解决方案不会保存关系）。

或者，看看this答案，我展示了如何覆盖RKObjectLoader以从URL本身检索页面信息。

编辑：这是我在评论中提到的类别：

.H

#import <RestKit/RestKit.h> 

typedef void(^RKObjectLoaderWillMapDataBlock)(id* mappableData); 

@interface RKObjectLoader (Extended) 

@property (nonatomic, copy) RKObjectLoaderWillMapDataBlock onWillMapData; 

@end 

与.m：

#import <objc/runtime.h> 

NSString* kOnWillMapDataKey = @"onWillMapData"; 

@implementation RKObjectLoader (Extended) 

- (RKObjectLoaderWillMapDataBlock) onWillMapData { 
    return objc_getAssociatedObject(self, &kOnWillMapDataKey); 
} 

- (void) setOnWillMapData:(RKObjectLoaderWillMapDataBlock) block { 
    objc_setAssociatedObject(self, &kOnWillMapDataKey, block, OBJC_ASSOCIATION_COPY); 
} 

- (RKObjectMappingResult*)mapResponseWithMappingProvider:(RKObjectMappingProvider*)mappingProvider toObject:(id)targetObject inContext:(RKObjectMappingProviderContext)context error:(NSError**)error { 
    id<RKParser> parser = [[RKParserRegistry sharedRegistry] parserForMIMEType:self.response.MIMEType]; 
    NSAssert1(parser, @"Cannot perform object load without a parser for MIME Type '%@'", self.response.MIMEType); 

    // Check that there is actually content in the response body for mapping. It is possible to get back a 200 response 
    // with the appropriate MIME Type with no content (such as for a successful PUT or DELETE). Make sure we don't generate an error 
    // in these cases 
    id bodyAsString = [self.response bodyAsString]; 
    RKLogTrace(@"bodyAsString: %@", bodyAsString); 
    if (bodyAsString == nil || [[bodyAsString stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]] length] == 0) { 
     RKLogDebug(@"Mapping attempted on empty response body..."); 
     if (self.targetObject) { 
      return [RKObjectMappingResult mappingResultWithDictionary:[NSDictionary dictionaryWithObject:self.targetObject forKey:@""]]; 
     } 

     return [RKObjectMappingResult mappingResultWithDictionary:[NSDictionary dictionary]]; 
    } 

    id parsedData = [parser objectFromString:bodyAsString error:error]; 
    if (parsedData == nil && error) { 
     return nil; 
    } 

    // Allow the delegate to manipulate the data 
    if ([self.delegate respondsToSelector:@selector(objectLoader:willMapData:)]) { 
     parsedData = [parsedData mutableCopy]; 
     [(NSObject<RKObjectLoaderDelegate>*)self.delegate objectLoader:self willMapData:&parsedData]; 
    } 

    if(self.onWillMapData) { 
     parsedData = [parsedData mutableCopy]; 
     self.onWillMapData(&parsedData); 
    } 

    RKObjectMapper* mapper = [RKObjectMapper mapperWithObject:parsedData mappingProvider:mappingProvider]; 
    mapper.targetObject = targetObject; 
    mapper.delegate = (id<RKObjectMapperDelegate>)self; 
    mapper.context = context; 
    RKObjectMappingResult* result = [mapper performMapping]; 

    // Log any mapping errors 
    if (mapper.errorCount > 0) { 
     RKLogError(@"Encountered errors during mapping: %@", [[mapper.errors valueForKey:@"localizedDescription"] componentsJoinedByString:@", "]); 
    } 

    // The object mapper will return a nil result if mapping failed 
    if (nil == result) { 
     // TODO: Construct a composite error that wraps up all the other errors. Should probably make it performMapping:&error when we have this? 
     if (error) *error = [mapper.errors lastObject]; 
     return nil; 
    } 

    return result; 
} 

@end