iosobjective-ccore-datanspredicate

NSPredicate Aggregate Operations with NONE

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

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

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

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

Is this a Bug?

DataModel

Solution

  • 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"]

    Explanation: Both predicates

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

    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"]

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

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