问题描述
抱歉，如果这是重复，20分钟的搜索没有产生这种确切的情况或解决方案。
Apologies if this is a duplicate, 20 minutes of searching didn't yield this exact situation or a solution.
我有一个Core数据堆栈， code> XClass ， YClass 和 ZClass 。 XClass 与 YClass 具有一对多的关系。 YClass 与 ZClass 有一对多的关系。
I have a Core Data stack with three classes XClass, YClass, and ZClass. XClass has a one-to-many relationship with YClass. YClass has a one-to-many relationship with ZClass.
使用 NSFetchedResultsController 的实例，我试图获取所有 XClass 的实例，其中至少有1个 YClass 至少有一个 ZClass 。
Using an instance of NSFetchedResultsController, I'm trying to fetch all instances of XClass for which at least 1 YClass has at least 1 ZClass.
定义如下：
// ...stuff
NSFetchRequest * fetchRequest = [NSFetchRequest new];
NSEntityDescription * entity = [NSEntityDescription entityForName:NSStringFromClass([XClass class])
inManagedObjectContext:managedObjectContext];
fetchRequest.entity = entity;
fetchRequest.predicate =
[NSPredicate predicateWithFormat:@"0 < SUBQUERY(yObjects, $y, $y.zObjects.@count > 0).@count"];
// ..instantiate NSFetchedResultsController and perform fetch
异常与消息：终止应用程序由于未捕获异常'NSInvalidArgumentException'，原因：包含KVC的键集合聚合其中不应该有一个;未能处理$ y.zObjects。@ count'
在其他地方，我已成功获取 YObject 实例与谓词 [NSPredicate predicateWithFormat：@zObjects。@ count> 0];
Elsewhere, I've successfully fetched YObject instances with the predicate [NSPredicate predicateWithFormat:@"zObjects.@count > 0"];
有人可以指点我的错误吗？非常感谢。
Can someone point me to what I'm doing wrong? Thank you much.
推荐答案
在SUBQUERY的谓词字符串中使用集合运算符时，NSPredicate对象此外，您似乎无法对子查询谓词中的集合进行操作。这是除非变量表示谓词中的集合。
It seems that NSPredicate objects violently when you use collection operators in the predicate string for the SUBQUERY. It also appears that you cannot operate on a collection in the subquery predicate. That is unless the variable represents a collection in the predicate.
BAD： SUBQUERY（yObjects，$ y，$ y.zObjects == NIL）> 0
OK： SUBQUERY（yObjects，$ y，SUBQUERY（$ y.zObjects $ z，$ z = = NIL）> 0） 0
以下表达式将所有非nil对象添加到SUBQUERY返回的过滤集合。换句话说，返回的集合将包含具有ZClass实例化的XClass的所有实例。
The following expression will add all non-nil objects to the filtered collection returned by the SUBQUERY. In other words, the returned collection will contain all instances of XClass with instantiations of ZClass.
[NSPredicate predicateWithFormat:@"yObjects.@count > 0 AND (SUBQUERY(yObjects, $y, (SUBQUERY($y.zObjects, $z, $z != NIL).@count > 0)).count > 0)"];
这篇关于Core Data SUBQUERY和NSFetchedResultsController的Keypath错误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！