问题描述
我有核心数据实体人员和边界.他们之间存在多对多关系(每个人可以有很多边界，每个边界可以有很多人).
I have Core Data Entities Person and Boundary. They have a many-to-many relationship (each person can have many boundaries, and each boundary can have many persons).
我正在尝试创建一个列表，列出Fred Fred也没有任何关系.
I am trying to create a list of what boundaries Person Fred doesn't have a relationship too.
Person *person = [Person MR_findFirstByAttribute:@"name" withValue:@"Fred"];
DLog(@"person.boundaries.count: %d", person.boundaries.count);
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"ANY persons != %@", person];
DLog(@"testBoundaries.count: %d", [Boundary MR_countOfEntitiesWithPredicate:predicate]);
我在数据库中有47个边界，Fred可以看到所有47个边界.因此，我希望我的提取操作将返回0:
I have 47 boundaries in the database, and Fred can see all 47. So I expect my fetch to return 0:
DEBUG | -[LoginViewController viewDidLoad] | person.boundaries.count: 47
DEBUG | -[LoginViewController viewDidLoad] | testBoundaries.count: 47
我的谓词怎么了?
推荐答案
[NSPredicate predicateWithFormat:@"ANY persons != %@", fred]
查找与Fred以外的任何其他人相关的所有对象.您想要的是
finds all objects that are related to any person other that Fred. What you want is
[NSPredicate predicateWithFormat:@"NOT(ANY persons = %@)", fred]
，并且此应该返回与Fred无关的所有对象.
and this should return all objects that are not related to Fred.
但是，似乎有一个核心数据错误，"NOT ANY"或"NONE"无法正常工作在谓词中比较 NSPredicate聚合运算与无.解决方法是使用SUBQUERY:
However, there seems to be a Core Data bug that "NOT ANY" or "NONE" do not work correctlyin a predicate,compare NSPredicate Aggregate Operations with NONE. The workaround is to use a SUBQUERY:
[NSPredicate predicateWithFormat:@"SUBQUERY(persons, $p, $p == %@).@count == 0", fred]
这篇关于NSPredicate带有！=?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！