核心数据多对多谓词 [英] Core Data many-to-many predicate

问题描述

我有两个实体通过多对多关系相关：

I have two entities which are related by a many-to-many relationship:

数据库< >>类别

换句话说，数据库可以有多个类别，一个类别可以与许多数据库相关联。

In other words, a database can have many categories and a category can be associated with many databases.

我需要一个 NSPredicate ，它将返回与给定数据库对象相关联的所有类别对象。任何帮助将不胜感激。

I need an NSPredicate that will return all Category objects associated with a given database object. Any help would be appreciated.

推荐答案

您不需要一个谓词。假设您有一个称为类别的关系，这是与您的类别实体的对多关系，则

You don't need a predicate. Given that you have a relationship called categories that is the to-many relationship to your Category entities, then

NSSet *categoriesForDatabase = database.categories;

如果你真的想使用谓词，那么它将是：

If you really want to use a predicate then it would be:

[NSPredicate predicateWithFormat:@"ANY databases = %@", database];

其中databases是Category实体上的多对多关系的名称，数据库是一个实例的数据库实体。

where "databases" is the name of the to many relationship on the Category entity and database is an instance of a Database entity.

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