Copy and deep copy for NSManagedObject graphs.

NSManagedObject+DeepCopying.m

/*
This makes some assumptions about your code, for example that you’ve got ownership rules set up properly. If a relationship to another entity uses the cascade deletion rule, it’s considered to be owned by the receiver, and thus will be copied by -deepCopyWithZone:.
*/

#import <Foundation/Foundation.h>
#import <CoreData/CoreData.h>

@interface NSManagedObject (RXCopying) <NSCopying>

-(void)setRelationshipsToObjectsByIDs:(id)objects;

-(id)deepCopyWithZone:(NSZone *)zone;
-(NSDictionary *)ownedIDs;

@end


@implementation NSManagedObject (RXCopying)

// copying
-(id)deepCopyWithZone:(NSZone *)zone {
	NSMutableDictionary *ownedIDs = [[self ownedIDs] mutableCopy];
	NSManagedObjectContext *context = [self managedObjectContext];
	id copied = [self copyWithZone: zone]; // -copyWithZone: copies the attributes for us

	for(NSManagedObjectID *key in [ownedIDs allKeys]) { // deep copy relationships
		id copiedObject = [[context objectWithID: key] copyWithZone: zone];
		[ownedIDs setObject: copiedObject forKey: key];
		[copiedObject release];
	}

	[copied setRelationshipsToObjectsByIDs: ownedIDs];
	for(NSManagedObjectID *key in [ownedIDs allKeys]) {
		[[ownedIDs objectForKey: key] setRelationshipsToObjectsByIDs: ownedIDs];
	}
	return copied;
}

-(id)copyWithZone:(NSZone *)zone { // shallow copy
	NSManagedObjectContext *context = [self managedObjectContext];
	id copied = [[[self class] allocWithZone: zone] initWithEntity: [self entity] insertIntoManagedObjectContext: context];

	for(NSString *key in [[[self entity] attributesByName] allKeys]) {
		[copied setValue: [self valueForKey: key] forKey: key];
	}

	for(NSString *key in [[[self entity] relationshipsByName] allKeys]) {
		[copied setValue: [self valueForKey: key] forKey: key];
	}
	return copied;
}

-(void)setRelationshipsToObjectsByIDs:(id)objects {
	id newReference = nil;
	NSDictionary *relationships = [[self entity] relationshipsByName];
	for(NSString *key in [relationships allKeys]) {
		if([[relationships objectForKey: key] isToMany]) {
			id references = [NSMutableSet set];
			for(id reference in [self valueForKey: key]) {
				if(newReference = [objects objectForKey: [reference objectID]]) {
					[references addObject: newReference];
				} else {
					[references addObject: reference];
				}
			}
			[self setValue: references forKey: key];
		} else {
			if(newReference = [objects objectForKey: [[self valueForKey: key] objectID]]) {
				[self setValue: newReference forKey: key];
			}
		}
	}
}

-(NSDictionary *)ownedIDs {
	NSDictionary *relationships = [[self entity] relationshipsByName];
	NSMutableDictionary *ownedIDs = [NSMutableDictionary dictionary];
	for(NSString *key in [relationships allKeys]) {
		id relationship = [relationships objectForKey: key];
		if([relationship deleteRule] == NSCascadeDeleteRule) { // ownership
			if([relationship isToMany]) {
				for(id child in [self valueForKey: key]) {
					[ownedIDs setObject: child forKey: [child objectID]];
					[ownedIDs addEntriesFromDictionary: [child ownedIDs]];
				}
			} else {
				id reference = [self valueForKey: key];
				[ownedIDs setObject: reference forKey: [reference objectID]];
			}
		}
	}
	return ownedIDs;
}

@end