多对多NSPredicate

Question

I have a model with a couple of to-many relationships.

System ->> Item ->> Code

I'm trying to write a predicate on a fetchRequest for System.

I only want to show Systems that have Items that have at least one Code.

I have tried a SUBQUERY but I just can't get it to work.

This is what I've tried...

[NSPredicate predicateWithFormat:@"(SUBQUERY(items, $x, $x.codes.@count != 0) != 0)"];

I've tried other various permutations of this but they all throw similar errors.

Could someone let me know what the correct predicate format is?

Answer 1

我认为你必须添加其他@count子查询：

[NSPredicate predicateWithFormat:@"SUBQUERY(items, $x, $x.codes.@count != 0).@count != 0"];