c# - 考虑时区的夏令时，将 UTC 日期时间转换为 future 时间

Question

我们有一个代表星期的系统，UTC 时间代表美国/芝加哥时区的开始和结束日期时间。星期从中部时间星期六早上的午夜开始，到中部时间星期五晚上的 23:59:59 结束，因此它们在数据库中的 UTC 条目是:

Week 1 - begin: 2015-10-24 05:00:00, end 2015-10-31 04:59:59
Week 2 - begin: 2015-10-31 05:00:00, end 2015-11-07 05:59:59
Week 3 - begin: 2015-11-07 06:00:00, end 2015-11-14 05:59:59
Week 4 - begin: 2015-11-14 06:00:00, end 2015-11-21 05:59:59
Week 5 - begin: 2015-11-21 06:00:00, end 2015-11-28 05:59:59

所以从上面的星期示例中，您可以看到从夏令时到标准时间的时间变化反射(reflect)在 10/31 和 11/7 之间。

我需要从给定的一周返回 N 周。我们的系统是 C# Azure worker 和网络角色，并在 Azure 云中运行(所有计算节点均为 UTC)。我的逻辑是，开始一周，将 N 周的工作日添加到一周的开始日期/时间，并要求开始日期大于原始开始日期且小于或等于计算 future 的日期。

var weeks = repository.Fetch(x => x.BeginDate <= nWeeksAheadUtc && x.BeginDate > week.BeginDate)l=;

除非结果答案中发生夏令时更改，否则此方法有效。由于时间的变化，基于将 21 天添加到第 1 周的开始日期来请求从第 1 周开始的接下来的 3 周只会返回第 2 周和第 3 周，因为计算的 future 值为 2015-11-14 05:00: 00，不包括第 4 周。

我已经通过以下方式使用 Nodatime 解决了这个问题:

LocalDateTime localDateTime = LocalDateTime.FromDateTime(week.BeginDate);
ZonedDateTime zonedDateTime = localDateTime.InZoneStrictly(DateTimeZoneProviders.Tzdb["UTC"]);
zonedDateTime = zonedDateTime.WithZone(DateTimeZoneProviders.Tzdb["America/Chicago"]);
DateTime centralDateTime = zonedDateTime.ToDateTimeUnspecified();
DateTime futureDateTime = centralDateTime.Add(TimeSpan.FromDays(weekCount*7));
localDateTime = LocalDateTime.FromDateTime(futureDateTime);
zonedDateTime = localDateTime.InZoneStrictly(DateTimeZoneProviders.Tzdb["America/Chicago"]);
DateTime nWeeksAheadUtc = zonedDateTime.ToDateTimeUtc();

var weeks = repository.Fetch(x => x.BeginDate <= nWeeksAheadUtc && x.BeginDate > week.BeginDate).OrderBy(x => x.RetailerWeekNumber).ToList();

虽然它起作用了，但对于跟随我维护此代码的开发人员来说，它似乎很麻烦而且不是很直观。是否有更简洁的方法通过我缺少的 Nodatime API 或(基本 C# 日期/时间)来执行此操作？

添加请求的示例 - 我刚刚为此类和这三个类创建了一个 UnitTest 项目:

Week.cs

using System;

namespace NodaTimeTest
{
    public class Week
    {
        public int Id { get; set; }
        public DateTime BeginDate { get; set; }
        public DateTime EndDate { get; set; }
    }
}

WeekService.cs

using NodaTime;
using System;
using System.Collections.Generic;
using System.Linq;

namespace NodaTimeTest
{
    public class WeekService
    {
        private readonly List<Week> repository;

        public WeekService()
        {
            this.repository = this.InitWeeks();
        }

        public List<Week> GetNextWeeks(int weekId, int weekCount)
        {
            Week week = this.repository.First(x => x.Id == weekId);

            // the meat - how to do this the right way?
            LocalDateTime localDateTime = LocalDateTime.FromDateTime(week.BeginDate);
            ZonedDateTime zonedDateTime = localDateTime.InZoneStrictly(DateTimeZoneProviders.Tzdb["UTC"]);
            zonedDateTime = zonedDateTime.WithZone(DateTimeZoneProviders.Tzdb["America/Chicago"]);
            DateTime centralDateTime = zonedDateTime.ToDateTimeUnspecified();
            DateTime futureDateTime = centralDateTime.Add(TimeSpan.FromDays(weekCount * 7));
            localDateTime = LocalDateTime.FromDateTime(futureDateTime);
            zonedDateTime = localDateTime.InZoneStrictly(DateTimeZoneProviders.Tzdb["America/Chicago"]);
            DateTime nWeeksAheadUtc = zonedDateTime.ToDateTimeUtc();

            var weeks = repository.Where(x => x.BeginDate <= nWeeksAheadUtc && x.BeginDate > week.BeginDate).OrderBy(x => x.Id).ToList();

            return weeks;
        }

        private List<Week> InitWeeks()
        {
            // sets up our list of 10 example dates in UTC encompassing America/Chicago daylight savings time change on 11/1
            // this means that all weeks are 168 hours long, except week "4", which is 169 hours long.
            var weeks = new List<Week>();
            DateTime beginDate = new DateTime(2015, 10, 10, 5, 0, 0, DateTimeKind.Utc);

            for (int i = 1; i <= 10; i++)
            {
                DateTime endDate = beginDate.AddDays(7).AddSeconds(-1);

                if (endDate.Date == new DateTime(2015, 11, 7, 0, 0, 0, DateTimeKind.Utc))
                {
                    endDate = endDate.AddHours(1);
                }

                weeks.Add(new Week { Id = i, BeginDate = beginDate, EndDate = endDate });

                beginDate = endDate.AddSeconds(1);
            }

            return weeks;
        }
    }
}

WeekServiceTest:

using Microsoft.VisualStudio.TestTools.UnitTesting;
using System.Linq;

namespace NodaTimeTest
{
    [TestClass]
    public class WeekServiceTest
    {
        private readonly WeekService weekService = new WeekService();

        [TestMethod]
        public void TestGetNextThreeWeeksOverDaylightTimeChange()
        {
            var result = this.weekService.GetNextWeeks(2, 3);

            Assert.AreEqual(3, result.ElementAt(0).Id);
            Assert.AreEqual(4, result.ElementAt(1).Id);
            Assert.AreEqual(5, result.ElementAt(2).Id);
        }

        [TestMethod]
        public void TestGetNextThreeWeeksWithNoDaylightTimeChange()
        {
            var result = this.weekService.GetNextWeeks(5, 3);

            Assert.AreEqual(6, result.ElementAt(0).Id);
            Assert.AreEqual(7, result.ElementAt(1).Id);
            Assert.AreEqual(8, result.ElementAt(2).Id);
        }
    }
}

Answer 1

好吧，如果我没听错的话，我想你可能想要这样的东西:

var zone = DateTimeZoneProviders.Tzdb["America/Chicago"];
var instantStart = Instant.FromDateTimeUtc(week.BeginDate);
var chicagoStart = instantStart.InZone(zone);
var localEnd = chicagoStart.LocalDateTime.PlusWeeks(weekCount);
var chicagoEnd = localEnd.InZoneLeniently(zone);
var bclEnd = chicagoEnd.ToDateTimeUtc();

var result = repository
    .Fetch(x => x.BeginDate >= week.BeginDate && x.BeginDate < bclEnd)
    .OrderBy(x => x.RetailerWeekNumber)
    .ToList();

请注意，我已经将下限设置为包含，将上限设置为不包含 - 这通常是最简单的做事方式。

如果你真的想，你当然可以把很多这样的东西串在一起:

var zone = DateTimeZoneProviders.Tzdb["America/Chicago"];
var bclEnd = Instant.FromDateTimeUtc(week.BeginDate)
    .InZone(zone)
    .LocalDateTime
    .PlusWeeks(weekCount)
    .InZoneLeniently(zone)
    .ToDateTimeUtc();

编辑:以上是如果您的 BeginDate 确实是您想要开始获取数据的时刻。这听起来像是在现实中，你想在开始时增加一周。那时它将是:

var zone = DateTimeZoneProviders.Tzdb["America/Chicago"];
var instantNow = Instant.FromDateTimeUtc(week.BeginDate);
var chicagoNow = instantStart.InZone(zone);
var localStart = chicagoNow.LocalDateTime.PlusWeeks(1);
var localEnd = localEnd(weekCount);
var bclStart = localStart.InZoneLeniently(zone).ToDateTimeUtc();
var bclEnd = localEnd.InZoneLeniently(zone).ToDateTimeUtc();

var result = repository
    .Fetch(x => x.BeginDate >= bclStart && x.BeginDate < bclEnd)
    .OrderBy(x => x.RetailerWeekNumber)
    .ToList();