出现错误是因为您的 JSON 将每个类别作为主键返回,即:一个 NSNumber。但是您的映射需要一个嵌套对象(将转换为 KVC 对象)。当您的地图尝试访问 KVC 对象(实际上是一个 NSNumber)上的属性“id”时,它会像这样崩溃。
我不确定它是否会起作用,但你可以尝试这样的事情:
RKManagedObjectMapping* categoryMapping = //something
categoryMapping.primaryKeyAttribute = @"categoryId";
[categoryMapping mapKeyPath: @"" toAttribute: @"categoryId"];
[..]
[postMapping mapKeyPath: @"categories" toRelationship: @"categories" withMapping: categoryMapping];
通常,您会使用 [RKManagedObjectMapping connectRelationship:withObjectForPrimaryKeyAttribute:] 方法,但我不知道这是否适用于多对多关系。您可能必须修改源代码才能执行此操作。要查看的代码在 [RKManagedObjectMappingOperation connectRelationship:] 内。
否则,如果可能的话,我建议您更改 JSON 源,使类别数组如下所示:“categories”:[{“categoryID:1},{“categoryID”:4}]。如果无法更改源,您可以使用委托方法或我在下面给出的 RKObjectLoader 扩展手动修改数据:
。H
typedef void(^RKObjectLoaderWillMapDataBlock)(id* mappableData);
@interface RKObjectLoader (Extended)
@property (nonatomic, copy) RKObjectLoaderWillMapDataBlock onWillMapData;
@end
.m
#import "RKObjectLoader+Extended.h"
#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 = AH_AUTORELEASE([parsedData mutableCopy]);
[(NSObject<RKObjectLoaderDelegate>*)self.delegate objectLoader:self willMapData:&parsedData];
}
if( self.onWillMapData ) {
parsedData = AH_AUTORELEASE([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