CoreData - 复制现有对象 [英] CoreData - Duplicate existing object

问题描述

您好，希望从我的核心数据db复制对象。现在我正在使用

Hi would like to duplicate an object from my core data db. Right now I'm using

        movement2 = [NSEntityDescription
                                     insertNewObjectForEntityForName:@"Movement" 
                                     inManagedObjectContext:self.managedObjectContext];

        movement2.name = movement.name;
        movement2.value = movement.value;
        movement2.date = movement.date;
        ... 

但是...

有没有办法将 move 的所有值复制到 NSManagedObject与NSObject不同，它提供了一个API来迭代它的一个代码？

Is there any way to copy all the values of movement to movement2, in one line of code?

推荐答案

其属性和关系。或者，而是实体描述。

NSManagedObject, unlike NSObject, provides an API to iterate over its attributes and relationships. Or, rather, it's entity description does. It isn't a one-liner, though.

movement2 = [NSEntityDescription insertNewObjectForEntityForName:@"Movement" 
                                          inManagedObjectContext:self.managedObjectContext];
NSEntityDescription *entity = [movement entity];
for (NSString *propertyName in [entity propertiesByName]) {
    [movement2 setValue:[movement valueForKey:propertyName] forKey:propertyName];
}

查看文档。

这将足以克隆大多数对象。如果数据库结构正确，那么以这种方式复制关系，它们的反向关系也将被更新。所以，如果你的运动与MovementDirection有一个关系，而MovementDirection有一个反向的一对多关系 parentMovements ，这个 parentMovements set将在调用上述代码后同时具有运动和 movement2 。

This will be enough to clone most of the objects. If database structure is correct, then copying relationships this way, their inverse ones will be updated as well. So, if your Movement had a relationship with, say, MovementDirection, and MovementDirection has an inverse 1-to-many relation parentMovements, this parentMovements set will have both movement and movement2 inside after you call the code above.

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