是否可以在“NSFetchRequest”中按子类排序而不添加其他属性？
我想按实体对 NSFetchRequest 的结果进行分组。这些实体都共享相同的抽象父级。例如：
animal
|
|-cat
|
|-dog
NSFetchRequest 将 includesSubentities 设置为 TRUE，将 entity 设置为 animal。可以将 NSFetchedResultsController 的 sectionNameKeyPath 设置为 entity.name，但不可能对 的 因为 sortDescriptors 执行相同的操作NSFetchRequestsortDescriptors 应用于存储的属性（即数据库中的数据，而不是类上的方法）。因此，按实体类型分组的唯一方法是向超类添加一个属性，子类可以使用该属性来标识自己。
这看起来很疯狂，因为它破坏了继承的用处。我查看了 SQLite 数据库，实体类型与属性存储在同一个表中，因此所需的数据已经就位。
总之：是否可以在不添加其他属性的情况下按 NSFetchRequest 中的子类进行排序？
I want to group the results of a NSFetchRequest by entity. The entities all share the same abstract parent. For example:
animal
|
|-cat
|
|-dog
The NSFetchRequest has includesSubentities set TRUE and entity set to animal. It is possible to set sectionNameKeyPath of NSFetchedResultsController to entity.name but it is not possible to do the same with the sortDescriptors of the NSFetchRequest due to the fact that the sortDescriptors are applied to the stored attributes (i.e. data in the database, not methods on the classes). Therefore the only way to group by entity type is to add an attribute to the superclass that subclasses can use to identify themselves.
This seems crazy as it undermines the usefulness of inheritance. I had a look in the SQLite database and the entity type is stored in the same table as the attributes so the required data is already in place.
In summary: Is it possible to sort by subclasses in an NSFetchRequest without adding additional attributes?
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我想答案是否定的。
获取和排序发生在存储中（对于 SQLLite 存储），因此属性需要成为数据模型的一部分。来自核心数据编程指南（持久存储功能）：
还
I think the answer is no.
Fetched and Sorting happens in the Store (for SQLLite store), so the attributes need to be part of the data model. From the core data programming guide (Persistent Store Features):
also