RestKit 0.20: Map relational data from local file - iphone

Question

I'm taking a local JSON file and trying to map it into a relational mapping. It works fine without the relationship, but once I add the relationship, I get an error.
JSON:
https://gist.github.com/4675414
Code:
// Get json from destination
NSString *myJSON = [[NSString alloc] initWithContentsOfFile:contentPath encoding:NSUTF8StringEncoding error:NULL];
NSString* MIMEType = #"application/json";
NSError* parseError;
NSData *data = [myJSON dataUsingEncoding:NSUTF8StringEncoding];
id parsedData = [RKMIMETypeSerialization objectFromData:data MIMEType:MIMEType error:&parseError];
if (parsedData == nil && parseError) {
NSLog(#"Cannot parse data: %#", parseError);
}
// 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 alloc] init];
RKMappingOperation* mapper = [[RKMappingOperation alloc] initWithSourceObject:[parsedData objectForKey:#"issue"] destinationObject:issue mapping:issueMapping];
RKManagedObjectMappingOperationDataSource *mappingDS = [RKManagedObjectMappingOperationDataSource new];
mapper.dataSource = mappingDS;
[mapper performMapping:&parseError];
NSLog(#"Parse error: %#", parseError);
NSLog(#"Issue title: %#", issue.title);
Error:
2013-01-30 13:07:42.486 uninkd[13722:907] *** Assertion failure in -[RKManagedObjectMappingOperationDataSource mappingOperation:targetObjectForRepresentation:withMapping:inRelationship:], /Users/holgersindbaek/Projects/Uninkd/Uninkd_IOS/Pods/RestKit/Code/CoreData/RKManagedObjectMappingOperationDataSource.m:232
2013-01-30 13:07:42.487 uninkd[13722:907] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'RKManagedObjectMappingOperationDataSource must be initialized with a managed object context.'
Error if I take away the data source:
2013-01-30 13:27:32.601 uninkd[13754:907] *** Assertion failure in -[RKMappingOperation applyRelationshipMappings], /Users/holgersindbaek/Projects/Uninkd/Uninkd_IOS/Pods/RestKit/Code/ObjectMapping/RKMappingOperation.m:699
2013-01-30 13:27:32.603 uninkd[13754:907] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Cannot perform relationship mapping without a data source'
Hope you can help.

Answer 1

This is because RKManagedObjectMappingOperationDataSource is expecting a managed object context, this is specifically for Core Data. Are you using core data?
Forget everything I previously said and use:
#import "RKObjectMappingOperationDataSource.h"
RKObjectMappingOperationDataSource *mappingDS = [RKObjectMappingOperationDataSource new];
mapper.dataSource = mappingDS;
instead of:
RKManagedObjectMappingOperationDataSource *mappingDS = [RKManagedObjectMappingOperationDataSource new];
mapper.dataSource = mappingDS;
A hint, don't use any classes that say ManagedObject if you're not using CoreData. This is referring to a ManagedObject in a ManagedObjectContext which is unique to CoreData. That being said, core data + restkit is awesome and you should check it out.