xcode iOS：一对一和多对多关系的“@count == 0”的 NSPredicate
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iOS: NSPredicate for "@count == 0" for both to-one and to-many relationships
提问by powertoold
I'd like to write a single NSPredicatethat would work for both to-one and to-many relationships:
我想写一首NSPredicate既适用于一对多关系又适用于多对多关系的单曲：
1) I have an NSMutableArraythat will run the filterUsingPredicatemethod
2) The NSPredicate will filter out a selected relationship that contain any objects in the relationship (again, for both to-one and to-many relationships).
1) 我有一个NSMutableArray将运行该filterUsingPredicate方法
2) NSPredicate 将过滤掉包含关系中任何对象的选定关系（同样，对于一对一和对多关系）。
I've tried something like predicateWithFormat:@"relationshipObjects.@count == 0", but this only seems to work for to-many relationships. Is there a similar predicate format that will work for both to-one and to-many relationships?
我试过类似的东西predicateWithFormat:@"relationshipObjects.@count == 0"，但这似乎只适用于多对多关系。是否有类似的谓词格式适用于一对一和多对多关系？
采纳答案by Nikita Pestrov
I think, you can use check for nilhere.
我想，你可以在这里使用 check for nil。
predicateWithFormat:@"relationshipOject != nil"
