带有 NONE 的 NSPredicate 聚合操作 [英] NSPredicate Aggregate Operations with NONE

问题描述

如何创建可以获取的谓词:所有问题不包含 answer.correct = "1".

How do I create a predicate that can fetch: all questions does not contain answer.correct = "1".

如果返回的数组包含0"和1"，则以下谓词不起作用:

The following predicate doesn't work if the returned array contain "0" and "1":

[NSPredicate predicateWithFormat:@"NONE answers.correct IN %@", [NSArray arrayWithObject:@"1"]];

也尝试过 NOT (ANY ...) :相同的结果

Also tried with NOT (ANY ...) : same result

这是一个错误吗?

推荐答案

简短回答: 要获取所有没有任何正确 == 1"答案"的对象，请使用以下命令子查询:

Short answer: To get all objects that do not have any "answer" with "correct == 1", use the following SUBQUERY:

[NSPredicate predicateWithFormat:@"SUBQUERY(answers, $a, $a.correct == 1).@count == 0"]

解释:两个谓词

[NSPredicate predicateWithFormat:@"NONE answers.correct == 1"]
[NSPredicate predicateWithFormat:@"NOT (ANY answers.correct == 1)"]

应该有效(据我了解 NOT 和 ANY 关键字)，但它们无效.它们返回与

should work (as I understand the NOT and ANY keywords) but they don't. They return the same result set as

[NSPredicate predicateWithFormat:@"ANY answers.correct != 1"]

通过设置启动参数 -com.apple.CoreData.SQLDebug 3 并检查 SQL 选择语句可以看出.

as can be seen by setting the launch argument -com.apple.CoreData.SQLDebug 3 and inspecting the SQL select statements.

这对我来说似乎是一个 Core Data 错误.使用 SUBQUERY 可以解决该问题.

This seems like a Core Data bug to me. Using the SUBQUERY is a workaround for that problem.

这篇关于带有 NONE 的 NSPredicate 聚合操作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IT屋！