如何截断.NET DateTime的毫秒数

Question

我正在尝试将传入请求的时间戳与数据库存储值进行比较.SQL Server当然会保留一些毫秒的精度,当读入.NET DateTime时,它包括那些毫秒.但是,对系统的传入请求不提供该精度,因此我需要简单地删除毫秒.

我觉得我错过了一些明显的东西,但我还没有找到一种优雅的方法(C#).

Answer 1

以下内容适用于具有小数毫秒的DateTime,并且还保留Kind属性(Local,Utc或Undefined).

DateTime dateTime = ... anything ...
dateTime = new DateTime(
    dateTime.Ticks - (dateTime.Ticks % TimeSpan.TicksPerSecond), 
    dateTime.Kind
    );

或等同和更短的:

dateTime = dateTime.AddTicks( - (dateTime.Ticks % TimeSpan.TicksPerSecond));

这可以推广到扩展方法:

public static DateTime Truncate(this DateTime dateTime, TimeSpan timeSpan)
{
    if (timeSpan == TimeSpan.Zero) return dateTime; // Or could throw an ArgumentException
    if (dateTime == DateTime.MinValue || dateTime == DateTime.MaxValue) return dateTime; // do not modify "guard" values
    return dateTime.AddTicks(-(dateTime.Ticks % timeSpan.Ticks));
}

使用如下:

dateTime = dateTime.Truncate(TimeSpan.FromMilliseconds(1)); // Truncate to whole ms
dateTime = dateTime.Truncate(TimeSpan.FromSeconds(1)); // Truncate to whole second
dateTime = dateTime.Truncate(TimeSpan.FromMinutes(1)); // Truncate to whole minute
...

Answer 2

var date = DateTime.Now;

date = new DateTime(date.Year, date.Month, date.Day, date.Hour, date.Minute, date.Second, date.Kind);

Answer 3

这是一个基于前一个答案的扩展方法,可以让你截断到任何分辨率......

用法:

DateTime myDateSansMilliseconds = myDate.Truncate(TimeSpan.TicksPerSecond);
DateTime myDateSansSeconds = myDate.Truncate(TimeSpan.TicksPerMinute)

类:

public static class DateTimeUtils
{
    /// <summary>
    /// <para>Truncates a DateTime to a specified resolution.</para>
    /// <para>A convenient source for resolution is TimeSpan.TicksPerXXXX constants.</para>
    /// </summary>
    /// <param name="date">The DateTime object to truncate</param>
    /// <param name="resolution">e.g. to round to nearest second, TimeSpan.TicksPerSecond</param>
    /// <returns>Truncated DateTime</returns>
    public static DateTime Truncate(this DateTime date, long resolution)
    {
        return new DateTime(date.Ticks - (date.Ticks % resolution), date.Kind);
    }
}

Answer 4

DateTime d = DateTime.Now;
d = d.AddMilliseconds(-d.Millisecond);

Answer 5

而不是丢弃毫秒然后比较,为什么不比较差异？

DateTime x; DateTime y;
bool areEqual = (x-y).TotalSeconds == 0;

要么

TimeSpan precision = TimeSpan.FromSeconds(1);
bool areEqual = (x-y).Duration() < precision;

Answer 6

有时您希望截断为基于日历的内容,例如年份或月份.这是一种扩展方法,可让您选择任何分辨率.

public enum DateTimeResolution
{
    Year, Month, Day, Hour, Minute, Second, Millisecond, Tick
}

public static DateTime Truncate(this DateTime self, DateTimeResolution resolution = DateTimeResolution.Second)
{
    switch (resolution)
    {
        case DateTimeResolution.Year:
            return new DateTime(self.Year, 1, 1, 0, 0, 0, 0, self.Kind);
        case DateTimeResolution.Month:
            return new DateTime(self.Year, self.Month, 1, 0, 0, 0, self.Kind);
        case DateTimeResolution.Day:
            return new DateTime(self.Year, self.Month, self.Day, 0, 0, 0, self.Kind);
        case DateTimeResolution.Hour:
            return self.AddTicks(-(self.Ticks % TimeSpan.TicksPerHour));
        case DateTimeResolution.Minute:
            return self.AddTicks(-(self.Ticks % TimeSpan.TicksPerMinute));
        case DateTimeResolution.Second:
            return self.AddTicks(-(self.Ticks % TimeSpan.TicksPerSecond));
        case DateTimeResolution.Millisecond:
            return self.AddTicks(-(self.Ticks % TimeSpan.TicksPerMillisecond));
        case DateTimeResolution.Tick:
            return self.AddTicks(0);
        default:
            throw new ArgumentException("unrecognized resolution", "resolution");
    }
}

Answer 7

不太明显,但速度提高了2倍以上:

// 10000000 runs

DateTime d = DateTime.Now;

// 484,375ms
d = new DateTime((d.Ticks / TimeSpan.TicksPerSecond) * TimeSpan.TicksPerSecond);

// 1296,875ms
d = d.AddMilliseconds(-d.Millisecond);

Answer 8

向下舍入到第二个：

dateTime.AddTicks(-dateTime.Ticks % TimeSpan.TicksPerSecond)

替换TicksPerMinute为四舍五入到分钟。

如果您的代码对性能敏感，请谨慎使用

new DateTime(date.Year, date.Month, date.Day, date.Hour, date.Minute, date.Second)

我的应用程序在System.DateTime.GetDatePart 中花费了 12% 的 CPU 时间。

Answer 9

一种轻松阅读的方法是...

//Remove milliseconds
DateTime date = DateTime.Now;
date = DateTime.ParseExact(date.ToString("yyyy-MM-dd HH:mm:ss"), "yyyy-MM-dd HH:mm:ss", null);

和更多...

//Remove seconds
DateTime date = DateTime.Now;
date = DateTime.ParseExact(date.ToString("yyyy-MM-dd HH:mm"), "yyyy-MM-dd HH:mm", null);

//Remove minutes
DateTime date = DateTime.Now;
date = DateTime.ParseExact(date.ToString("yyyy-MM-dd HH"), "yyyy-MM-dd HH", null);

//and go on...

据我了解，它很容易理解，但缺乏性能。

Answer 10

不是最快的解决方案，但简单易懂：

DateTime d = DateTime.Now;
d = d.Date.AddHours(d.Hour).AddMinutes(d.Minute).AddSeconds(d.Second)