如何复制或复制核心数据托管对象? [英] How can I duplicate, or copy a Core Data Managed Object?

问题描述

我有一个管理对象(A")，它包含各种属性和关系类型，它的关系也有自己的属性&关系.我想做的是复制"或复制"以对象A"为根的整个对象图，从而创建一个与A"非常相似的新对象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"(或其子项)包含的任何关系都不应指向与A"相关的对象.应该有一个全新的对象图，具有完整的相似关系，并且所有对象都具有相同的属性，但当然有不同的 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.

有明显的手动方法可以做到这一点，但我希望了解一种更简单的方法，这在 Core Data 文档中并不完全清楚.

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

这是我创建的一个类，用于执行托管对象的深度复制":属性和关系.请注意，这不会检查对象图中的循环.(感谢 Jaanus 的出发点...)

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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