NSPredicate字符串中的isSubsetOfSet [英] isSubsetOfSet in NSPredicate string

问题描述

我很难检查nsorderedset是否是NSPredicate字符串中另一个nsorderedset的子集.

I have difficulties checking if a nsorderedset is a subset of another nsorderedset in a NSPredicate string.

我可以通过以下代码块实现结果:

I can achieve the result with the block below:

request.predicate = [NSPredicate predicateWithBlock:^BOOL(id object, NSDictionary *bindings) {
    NSOrderedSet *biggerSet = [object valueForKey:@"attributeName"];
    return [smallerSet isSubsetOfOrderedSet:biggerSet];
}];

但是我相信字符串格式的性能可能更高(我错了吗?).

but I believe that in string format could be more performant (am I wrong?).

尝试了诸如@属性CONTAINS％@"和@％@ IN属性"之类的东西，但是没有运气.

tried things like @"attribute CONTAINS %@" and @"%@ IN attribute" but with no luck.

感谢您的帮助.

推荐答案

类似的方法应该起作用:

Something like this should work:

NS(Ordered)Set *smallerSet = …
request.predicate =
  [NSPredicate predicateWithFormat:@"SUBQUERY(attribute, $a, $a IN %@).@count == %lu",
         smallerSet, (unsigned long)[smallerSet count]];

谓词检查 smallerSet 中包含的属性"值的数量是否为等于 smallerSet 中的元素数.如果是，则 smallerSet 必须是属性"集的子集.

The predicate checks if the number of "attribute" values contained in smallerSet is equal to the number of elements in smallerSet. If yes, then smallerSet must be a subset of the "attribute" set.

基于字符串的谓词通常不会比基于块的谓词快(比较 https://stackoverflow.com/a/21158730/1187415 ).但是核心数据获取请求(带有SQlite存储文件)不能使用基于块的谓词.

A string based predicate is not generally faster than a block based (compare https://stackoverflow.com/a/21158730/1187415). But a Core Data fetch request (with a SQlite store file) cannot use block based predicates.

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