cocoacore-datansmanagedobject

How can I duplicate, or copy a Core Data Managed Object?


I have a managed object ("A") that contains various attributes and types of relationships, and its relationships also have their own attributes & relationships. What I would like to do is to "copy" or "duplicate" the entire object graph rooted at object "A", and thus creating a new object "B" that is very similar to "A".

To be more specific, none of the relationships contained by "B" (or its children) should point to objects related to "A". There should be an entirely new object graph with similar relationships intact, and all objects having the same attributes, but of course different id's.

There is the obvious manual way to do this, but I was hoping to learn of a simpler means of doing so which was not totally apparent from the Core Data documentation.

TIA!


Solution

  • Here's a class I created to perform a "deep copy" of managed objects: attributes and relationships. Note that this does not check against loops in the object graph. (Thanks Jaanus for the starting off point...)

    @interface ManagedObjectCloner : NSObject {
    }
    +(NSManagedObject *)clone:(NSManagedObject *)source inContext:(NSManagedObjectContext *)context;
    @end
    
    @implementation ManagedObjectCloner
    
    +(NSManagedObject *) clone:(NSManagedObject *)source inContext:(NSManagedObjectContext *)context{
        NSString *entityName = [[source entity] name];
    
        //create new object in data store
        NSManagedObject *cloned = [NSEntityDescription
                                   insertNewObjectForEntityForName:entityName
                                   inManagedObjectContext:context];
    
        //loop through all attributes and assign then to the clone
        NSDictionary *attributes = [[NSEntityDescription
                                     entityForName:entityName
                                     inManagedObjectContext:context] attributesByName];
    
        for (NSString *attr in attributes) {
            [cloned setValue:[source valueForKey:attr] forKey:attr];
        }
    
        //Loop through all relationships, and clone them.
        NSDictionary *relationships = [[NSEntityDescription
                                       entityForName:entityName
                                       inManagedObjectContext:context] relationshipsByName];
        for (NSRelationshipDescription *rel in relationships){
            NSString *keyName = [NSString stringWithFormat:@"%@",rel];
            //get a set of all objects in the relationship
            NSMutableSet *sourceSet = [source mutableSetValueForKey:keyName];
            NSMutableSet *clonedSet = [cloned mutableSetValueForKey:keyName];
            NSEnumerator *e = [sourceSet objectEnumerator];
            NSManagedObject *relatedObject;
            while ( relatedObject = [e nextObject]){
                //Clone it, and add clone to set
                NSManagedObject *clonedRelatedObject = [ManagedObjectCloner clone:relatedObject 
                                                              inContext:context];
                [clonedSet addObject:clonedRelatedObject];
            }
    
        }
    
        return cloned;
    }
    
    
    @end