问题描述
假设变量A和B在同一个托管对象上下文中保存托管对象的实例。我需要确保它们与持久存储中相同的记录相关联。核心数据编程中的部分指南说：
Let's say variable A and B hold instances of managed objects in the same managed object context. I need to make sure that they are associated with the same "record" in the persistent store. The section on Faulting and Uniquing in the Core Data Programming Guide says that:
从这里，似乎指针比较足以满足我的目的。
From this, it seems that a pointer comparison is sufficient for my purpose. Or does it ever make sense to use isEqual: to compare managed objects in the same context?
推荐答案
使用 == 来确定两个指针是否指向同一个对象。使用 -isEqual 来确定两个对象是否为等于，其中相等的概念取决于被比较的对象。 -isEqual：通常会比较 -hash 方法返回的值。我之前写过，如果两个托管对象包含相同的值，则 -isEqual：可能会返回true。这显然是不对的。文档中有一些注意事项，确保可变对象的哈希值在集合中不会改变，并且知道给定对象是否在集合中可能很困难。看起来，管理对象的哈希不依赖于该对象包含的数据，并且更有可能它连接到关于对象的不可变的东西;对象的 -objectID 值似乎是一个可能的候选人。
Use == to determine if two pointers point to the same object. Use -isEqual to determine if two objects are "equal", where the notion of equality depends on the objects being compared. -isEqual: normally compares the values returned by the -hash method. I wrote previously that it seemed possible that -isEqual: might return true if two managed objects contain the same values. That's clearly not right. There are some caveats in the docs about making sure that the hash value for a mutable object doesn't change while it's in a collection, and that knowing whether a given object is in a collection can be difficult. It seems certain that the hash for a managed object doesn't depend on the data that that object contains, and much more likely that it's connected to something immutable about the object; the object's -objectID value seems a likely candidate.
鉴于这一切，我改变了我的意见; ）。每个记录只在给定的上下文中表示一次，因此 == 可能是安全的，但 -isEqual：更好地表达你的意图。
Given all that, I'm changing my opinion ;-). Each record is only represented once in a given context, so == is probably safe, but -isEqual: seems to better express your intention.
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