我可以根据子 class 对象的属性创建谓词吗？

Question

我有两个 classes：Activity 和 Action。 Activity是parent class，Action是child，这是一对多的关系。在设置 NSFetchedResultsController 时，我想设置一个基于子 class 属性的谓词。这是一个例子...

fetchRequest.predicate = NSPredicate(format: "filter only activities that have actions which have their date property equalling today")

如果我要使用 for in 循环过滤活动，这就是它的样子...

for activity in activities
{
    if activity.actions != nil
    {
        for action in activity.actions
        {
            if action.date == today
            {
                // add activity to filtered array
            }
        }
    }
}

Answer 1

您可以在 NSPredicate 中使用 SUBQUERY。这里我用了一个NSArray作为示范。

let today = Date()

let array: NSArray = [
    Activity(actions: [
        Action(date: today)
        ]),
    Activity(actions: [
        Action(date: Date(timeIntervalSince1970: 0))
        ])
]

// here is your predicate
let result = array.filtered(using: NSPredicate(format: "SUBQUERY(actions, $action, $action.date == %@) .@count > 0", today as CVarArg))
print(result.count) // 1

请注意，我在这里使用 == 来比较日期，这意味着只有日期正好等于 today 时才会匹配。如果 "today" 你的意思是 "any time in the 24 hours"，那么你将不得不使用 this question:

中建议的答案

func getLastAndNextMidnight(date: Date) -> (Date, Date) {
    let dateComponents = Calendar.current.dateComponents([.year, .month, .day], from: date)
    var oneDay = DateComponents()
    oneDay.day = 1
    let lastMidnight = Calendar.current.date(from: dateComponents)!
    let nextMidnight = Calendar.current.date(byAdding: oneDay, to: lastMidnight)!
    return (lastMidnight, nextMidnight)
}
let midnights = getLastAndNextMidnight(date: today)
let result = array.filtered(using: NSPredicate(format: "SUBQUERY(actions, $action, ($action.date >= %@) AND ($action.date <= %@)) .@count > 0", midnights.0 as CVarArg, midnights.1 as CVarArg))
print(result.count)

Answer 2

今天有什么活动吗？谓词格式：

"ANY actions.date == today"

我可以根据子 class 对象的属性创建谓词吗？

Can I create a predicate based on the properties of child class objects?

core-data

nspredicate

nsfetchedresultscontroller

swift