public enum Ability: String {
case newcomer = "Newcomer"
case beginner = "Beginner"
case intermediate = "Intermediate"
case advanced = "Advanced"
}
public enum Group: String {
case solo = "Solo"
case duo = "Duo"
case team = "Team"
}
我想找到符合以下条件的所有性能。
ability == "Beginner"
group == "Duo"
performers == "Jane Davies" && "Alice Evans"
The documentation表明不支持核心数据中的聚合操作,这令人惊讶。此类问题已asked before在这里并建议使用“任何”。
据我了解,“Any”会返回包含“Jane”或“Alice”或“Jane & Alice”的表演,对吗?我只想要包含“Jane & Alice”的表演。
如何为这个查询编写谓词?
谢谢
最佳答案
对于(不同的)Performer 对象的列表,以下谓词应该有效 找到与这些对象完全相关的所有 Performance 对象 表演者:
let perf1 = ... // Performer object for "Jane Davies"
let perf2 = ... // Performer object for "Alice Evans"
let list = [perf1, perf2]
let predicate = NSPredicate(format: "performers.@count = %ld AND ALL performers in %@", list.count, list)
但显然不是。解决方法是使用子查询:
let predicate = NSPredicate(format: "performers.@count = %ld AND SUBQUERY(performers, $p, $p in %@).@count = %ld",
list.count, list, list.count)
关于ios - 针对特定集合的多对多关系核心数据查询,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/47000763/