Question

我有两节课：活动和动作。活动是父类，动作是孩子，这是一对多的关系。在设置NSFetchedResultsController时，我想基于子类的属性设置一个谓词。这是一个例子...

PHP

如果我要使用for in循环过滤活动，那将是这样...

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

Answer 1

您可以在SUBQUERY中使用NSPredicate。在这里，我以NSArray为例。

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，这意味着只有在日期完全等于today的情况下，它才会匹配。如果“今天”是指“ 24小时内的任何时间”，那么您将不得不使用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

今天有采取任何行动吗？谓词格式：

"ANY actions.date == today"

我可以基于子类对象的属性创建谓词吗？

2 个答案: