过滤一对多的导航属性

Question

我有一个模型类别，关系属性文章是一个NSOrderedSet。 现在我想用满足某个条件的文章获取所有类别，在SQL中我会写：

SELECT * 
FROM Category AS cat
JOIN Article AS art ON art.categoryId = cat.categoryId AND art.gender='m';

我尝试过：

NSPredicate(format: "articles.gender like %@ OR articles.gender = %@", gender.lowercased(), "n")

我收到以下错误：

  

***由于未捕获的异常'NSInvalidArgumentException'终止应用，原因：'此处不允许使用多对键'

完整代码：

    let ctx = self.Context()

    var gender = UserDefaults.standard.string(forKey: "gender_preference") ?? "*"
    if gender.uppercased() == "N" { gender = "*" }

    // Create Fetch Request
    let fetchRequest: NSFetchRequest = ArticleCategory.fetchRequest()
    let predicate = NSPredicate(format: "articles.gender like %@ or articles.gender = %@", gender, "n")
    fetchRequest.predicate = predicate

    // sort by name
    let sort = NSSortDescriptor(key: "name", ascending: true)
    fetchRequest.sortDescriptors = [sort]

    do {

        let result = try ctx.fetch(fetchRequest)
        return result

    } catch {

        print(error)

    }

    return []

亲切的问候

编辑：

Answer 1

我发现使用SUBQUERY更可靠，而不是ANY，ALL，NONE或SOME，尤其是复合条款。如果符合条件的文章计数大于零，则获取其中任何文章满足条件的类别等同于获取：

let predicate = NSPredicate(format: "SUBQUERY(articles, $a, $a.gender like %@ OR $a.gender == %@).@count > 0", gender, "n")