NSPredicate在NSFetchedResultsController中表现奇怪 [英] NSPredicate acting strange in NSFetchedResultsController

问题描述

我觉得这应该很简单，但它的行为很奇怪。

I feel as if this should be very simple, but it's behaving strangely.

我有3个实体，有这样的关系

I have 3 entities, with a relationship as such

实体A < - >>实体B <实体C

Entity A <-->> Entity B <<--> Entity C

我有一个NSFetchedResults控制器， m尝试使用以下谓词过滤实体A的结果。

I have an NSFetchedResults controller and I'm trying to filter the results of Entity A using the following predicate.

[NSPredicate predicateWithFormat:@"NONE entityB.entityC == %@", self.entityC];

当我尝试运行应用程序时，输出没有显示任何结果。我可以稍微改变谓词：

When I try and run the app, the output shows no results. I can alter the predicate slightly to:

[NSPredicate predicateWithFormat:@"ANY entityB.entityC == %@", self.entityC];

它只显示我想要过滤掉的结果。

And it shows me only the results that I want it to filter out.

为什么会发生这种情况？

Why is this happening?

推荐答案

我想你可能需要 SUBQUERY 表达式：

I think you may want a SUBQUERY expression:

@"SUBQUERY(entityB, $x, $x.entityC == %@).@count == 0"

虽然，它可能工作：

@"NOT (ANY entityB.entityC == %@)"

（注意：我没有测试第二个选项）

(note: I haven't tested the second option)

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