我有一些使用Xcode生成的NSManagedObject的子类。 我为这些类编写了一些验证代码（ validateForInsert: :)，但每次更新数据模型并重新生成子类时，所有这些验证代码都会消失。 有些人建议我使用类别来扩展这些类而不是在其中编写代码，但根据苹果的文档，用类别覆盖方法是一种非常糟糕的做法，可能会导致未定义的行为。 
 
 我还尝试将这些生成的类子类化。 我有一个名为DBEntityOne的生成类，其子类称为EntityOne 。 EntityOne与EntityTwo具有一对一的关系，由DBEntityTwo （生成）和EntityTwo 。 但是，每当我尝试将EntityTwo与EntityOne实例关联时，我得到的是DBEntityTwo而不是EntityTwo 。 
 
 所以我该怎么做？ 我应该放弃自动代码生成并自己编写所有实体类吗？ 

I have some subclasses of NSManagedObject generated using Xcode. I wrote some validation codes (validateForInsert:) to those classes, but every time I update the data model and regenerate the subclasses, all those validation codes disappear. Some people suggest me to use categories to extend these classes instead of writing codes in it, but according to apple's document, overriding methods with categories is a very bad practice and can lead to undefined behaviour. 
 
I also tried to subclass those generated classes. I have a generated class called DBEntityOne and its subclass is called EntityOne. EntityOne has an one-to-one relationship with EntityTwo, which is represented by DBEntityTwo(generated) and EntityTwo. However, whenever I try to get the EntityTwo associated with an EntityOne instance, what I get is a DBEntityTwo instead of EntityTwo. 
 
So what should I do? Should I give up the automatic code generation and write all the entity classes by myself?

原文：https://stackoverflow.com/questions/28291182