核心数据谓词按今天的日期过滤

Question

我有这方面的问题,我没有找到一个正确的答案所以我会在这里留下一个小教程.

目标是在今天的日期过滤提取的对象.

注意:它与Swift 3兼容.

Answer 1

您不能简单地使用您的日期与今天的日期进行比较:

let today = Date()
let datePredicate = NSPredicate(format: "%K == %@", #keyPath(ModelType.date), today)

它不会显示任何内容,因为您的日期不太可能是完全比较日期(它也包括秒和毫秒)

解决方案是这样的:

// Get the current calendar with local time zone
var calendar = Calendar.current
calendar.timeZone = NSTimeZone.local

// Get today's beginning & end
let dateFrom = calendar.startOfDay(for: Date()) // eg. 2016-10-10 00:00:00
let dateTo = calendar.date(byAdding: .day, value: 1, to: dateFrom)
// Note: Times are printed in UTC. Depending on where you live it won't print 00:00:00 but it will work with UTC times which can be converted to local time

// Set predicate as date being today's date
let fromPredicate = NSPredicate(format: "%@ >= %@", date as NSDate, dateFrom as NSDate)
let toPredicate = NSPredicate(format: "%@ < %@", date as NSDate, dateTo as NSDate)
let datePredicate = NSCompoundPredicate(andPredicateWithSubpredicates: [fromPredicate, toPredicate])
fetchRequest.predicate = datePredicate

它是迄今为止仅显示具有今天日期的对象的最简单和最短的方式.

Answer 2

在 swift4 中，Lawrence413 的可以简化一点：

//Get today's beginning & end
let dateFrom = calendar.startOfDay(for: Date()) // eg. 2016-10-10 00:00:00
let dateTo = calendar.date(byAdding: .day, value: 1, to: dateFrom)

它去掉了component部分，使代码具有更好的可读性。

Answer 3

添加到 Lawrence413 的答案中可能会有所帮助，即要过滤具有保存今天日期的属性的记录列表，您可以使用：

let fromPredicate = NSPredicate(format: "datetime >= %@", dateFrom as NSDate)
let toPredicate   = NSPredicate(format: "datetime < %@",  dateToUnwrapped as NSDate)

...其中“日期时间是属性的名称”