If I map this with only the issue mapping and leave out the article relationship, then everything is fine. If I include the article relationship, then I get the error: Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'RKManagedObjectMappingOperationDataSource must be initialized with a managed object context.'

Mapping Local File

        //Setting up objectmapping for issue
        RKObjectMapping *issueMapping = [RKObjectMapping mappingForClass:[Issue class]];
        [issueMapping addAttributeMappingsFromDictionary:@{
         @"title":                      @"title",
         @"description":                @"description",
         @"cover_url":                  @"cover_url",
         @"published_at":               @"published_at",
         @"issue_number":               @"issue_number"
         }];
        
        //Setting up objectmapping for article
        RKObjectMapping *articleMapping = [RKObjectMapping mappingForClass:[Article class]];
        [articleMapping addAttributeMappingsFromDictionary:@{
         @"title":                      @"title",
         @"main_text":                  @"main_text",
         @"article_image_url":          @"article_image_url"
         }];
        [issueMapping addPropertyMapping:[RKRelationshipMapping relationshipMappingFromKeyPath:@"articles" toKeyPath:@"articles" withMapping:articleMapping]];
        
        Issue *issue = [Issue new];
        RKMappingOperation *operation = [[RKMappingOperation alloc] initWithSourceObject:[parsedData objectForKey:@"issue"] destinationObject:issue mapping:issueMapping];
        RKManagedObjectMappingOperationDataSource *dataSource = [RKManagedObjectMappingOperationDataSource new];
        operation.dataSource = dataSource;
        [operation start];
        NSLog(@"Parse error: %@", parseError);
        NSLog(@"Issue title: %@", issue.title);

Its hard for me to tell exactly what you are doing wrong here, but there are 2 possibilities:

1. If your Issue and Article classes are backed by Core Data, then you need to use RKEntityMapping and call the designated initializer on RKManagedObjectMappingOperationDataSource -- i.e.

NSManagedObjectContext *context = [RKManagedObjectStore defaultStore].mainQueueManagedObjectContext;
RKFetchRequestManagedObjectCache *cache = [RKFetchRequestManagedObjectCache new];
RKManagedObjectMappingOperationDataSource *dataSource = [[RKManagedObjectMappingOperationDataSource alloc] initWithManagedObjectContext:context cache:cache];

or

1. You are mapping to non-Core Data backed classes and using the wrong data source. Just replace your data source initialization with this:

RKObjectMappingOperationDataSource *dataSource = [RKObjectMappingOperationDataSource new];

Hi Blake
I am having exactly the same issue.
Is there any recommended way to parse a local json string with RestKit?