如何使用NSPredicate使用今天的NSDate获取对象? [英] How fetch objects with NSDate of today using NSPredicate?

问题描述

我的核心数据模型和涉及日期的提取请求陷入了困境.

I'm stuck in a problem with my Core Data model and a fetch request that involves dates.

我在具有NSDate属性的实体中有一些对象；我需要提取日期为今天的对象，但是我总是从以下代码中得到零:

I have some objects in a entity with a NSDate attribute; I need to extract the objects with the date of today but I always get nil from this code:

public func getObjectsOfToday() -> Array<myObject>?
{
    let entityDescription = NSEntityDescription.entityForName("Objects", inManagedObjectContext: DataAccess.sharedInstance.managedObjectContext)

    let request = NSFetchRequest()
    request.entity = entityDescription
    request.returnsObjectsAsFaults = false

    let today = NSDate()
    request.predicate = NSPredicate(format: "(dateStart => %@) AND (dateStart <= %@)", today, today)

    var objects: [AnyObject]?
    do
    {
        objects = try DataAccess.sharedInstance.managedObjectContext.executeFetchRequest(request)
    }
    catch let error as NSError
    {
        print(error)
        objects = nil
    }

    return objects as? Array<Objects>
}

我认为这是NSPredicate的问题，因为它还考虑了小时，分钟和秒.如果我今天打印的话是这样的:

the problem I think it's the NSPredicate because it considers also hours, minute and seconds. If I print today is something like:

今天的印刷说明:2016-02-28 22:02:01 +0000

Printing description of today: 2016-02-28 22:02:01 +0000

但是我想获取日期相同的对象，而忽略小时，分钟和秒.我该怎么办?

我还尝试使用组件创建另一个NSDate:

I also tried to create another NSDate using components:

let components = cal.components([.Day , .Month, .Year ], fromDate: today)
let newDate = cal.dateFromComponents(components)

但是结果是一样的.我在做什么错了?

but the result it's the same. What am I doing wrong?

推荐答案

我要做的是将它与一天的开始和结束时间进行比较，并具有几个辅助函数来计算它们:

What I do is compare it to the start and end of the day and have a couple helper functions to calculate them:

class DateHelper{
    internal class func startOfDay(day: NSDate) -> NSDate {
        let gregorian = NSCalendar(calendarIdentifier: NSCalendarIdentifierGregorian)
        let unitFlags: NSCalendarUnit = [.Minute, .Hour, .Day, .Month, .Year]
        let todayComponents = gregorian!.components(unitFlags, fromDate: day)
        todayComponents.hour = 0
        todayComponents.minute = 0
        return (gregorian?.dateFromComponents(todayComponents))!
    }

    internal class func endOfDay(day: NSDate) -> NSDate {
        let gregorian = NSCalendar(calendarIdentifier: NSCalendarIdentifierGregorian)
        let unitFlags: NSCalendarUnit = [.Minute, .Hour, .Day, .Month, .Year]
        let todayComponents = gregorian!.components(unitFlags, fromDate: day)
        todayComponents.hour = 23
        todayComponents.minute = 59
        return (gregorian?.dateFromComponents(todayComponents))!
    }
}

因此，在您的代码中，您将调用:

So in your code, you would call:

request.predicate = NSPredicate(format: "(dateStart => %@) AND (dateStart <= %@)", DateHelper.startOfDay(today), DateHelper.endOfDay(today))

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