ios - NSPredicate 过滤器对多与子对象属性

Question

我有一个我认为很简单的问题。我正在尝试过滤一些核心数据，其中我有一个父对象，该对象与子对象具有一对多关系，并且该子对象具有字符串 id。我想获取所有没有子对象具有特定 id 的父对象。

我尝试过 !(ANY... LIKE) 以及 !(ANY..==) 和 NONE 等和 == 和 ALL Children.id != otherid

我的查询如下所示:

NSFetchRequest* fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Parent"];

NSPredicate* predicate = [NSPredicate predicateWithFormat:@"NONE children.id LIKE %@",otherID];
[fetchRequest setPredicate: predicate];
NSError* error;
NSArray* allParents = [[DataManager context] executeFetchRequest:fetchRequest error:&error];
//sanity check the predicate
for (Parent* p in allParents) {
    for (Child* c in p.children) {
        if([c.id isEqualToString:otherID]){
            NSLog(@"PREDICATE FAIL!");
        }
    }
}

我是否遗漏了 NSPredicate 的某些内容？ CoreData 是否允许这种类型的过滤？更好的解决方案？

Answer 1

我发现了一个类似的问题，尽管不太明显。事实证明，答案是棘手的 SUBQUERY。以下是我追寻的原因:

NSPredicate Aggregate Operations with NONE

这里还有关于 SUBQUERY 的更开放的解释:

http://funwithobjc.tumblr.com/post/2726166818/what-the-heck-is-subquery

结果谓词是:

//in children get a $child and group all the $child objects together
//where the ids match, if that groups count is 0 we know 
//the parent has no child with that id
[NSPredicate predicateWithFormat:
   @"SUBQUERY(children, $child, $child.id == %@).@count == 0",objectId];