RestKit：連接不在響應中的關係

Question

假設在我的數據模型中，我有Pages，其中有許多Comments。

我想連接模型中的一個關係，該關係從Comment返回到它所屬的Page，但Page對象不嵌套在響應中，也沒有任何可以標識父頁面的主鍵出現在回覆中。

當我撥打loadObjectsAtResourcePath時，加載的所有Comments都應該屬於固定的已知Page對象。我可以掛鉤的關係的一種方式是做：

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

但我希望有一個更好的辦法。請注意，我不能使用connectRelationship系列方法，因爲響應中沒有主鍵，可以讓我將每個Comment都掛鉤到Page。

Answer 1

您可以使用委託方法- (void)objectLoader:(RKObjectLoader *)loader willMapData:(inout id *)mappableData在映射步驟之前注入額外的參數。它確保在使用核心數據時，RestKit可以正確保存對象和關係（請注意，上面給出的解決方案不會保存關係）。

或者，看看this答案，我展示瞭如何覆蓋RKObjectLoader以從URL本身檢索頁面信息。

編輯：這是我在評論中提到的類別：

.H

#import <RestKit/RestKit.h> 

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

@interface RKObjectLoader (Extended) 

@property (nonatomic, copy) RKObjectLoaderWillMapDataBlock onWillMapData; 

@end 

與.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