如何复制或复制Core Data Managed Object？ [英] How can I duplicate, or copy a Core Data Managed Object?

问题描述

我有一个包含各种属性和关系类型的托管对象（A），它的关系也有自己的属性&关系。我想要做的是复制或复制以对象A为根的整个对象图，从而创建一个非常类似于A的新对象B。

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".

更具体地说，B（或其子代）包含的关系都不应指向与A相关的对象。应该有一个完全相似的关系完整的新对象图，所有对象具有相同的属性，但当然不同的id。

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.

有明显的手动方式这是，但我希望学习一个更简单的方法这是不完全明显从核心数据文档。

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！

推荐答案

以下是我创建的一个类，用于对托管对象执行深度复制：属性和关系。请注意，这不会检查对象图中的循环。 （感谢Jaanus的起点...）

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

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