领域驱动(DDD)实战---月份类YearMonth
Net中有一个DateTime结构类，涉及时间和日期，这个类大量使用。可是，他的名称已经显著的表明他是表达某个具体的时刻。当我们不需要每天的具体时间时，如：我的程序逻辑仅仅需要年月（发工资的周期？），这个DateTime显得有些累赘，甚至不合用。
一般人们解决的方式，仍然使用DateTime而从数据上，设置hour,mintue等等为0。 然而，这与DDD的理念相背，名称有与含义有偏差，另外，数据一致性的维护，散布在各个角落，如，保证日期始终为1，小时，分钟为0。另外，与月份相关的功能，如：得到下一个月份，要么用DateTime本身的功能（AddMonths),要么提炼出一个Utitlies出来。 前者，需要开发者时刻重复DateTime到YearMonth的映射逻辑，后者是个反模式。 （本文版权属于© 2012 - 2013 予沁安）
这里，我创建出一个基本类型YearMonth，可以作为代码的基本砖块。
[代码] 用Extension的方式，来增强代码流畅性和可读性
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public static class YearMonthExtension { public static YearMonth year(this int year, int month) { return new YearMonth(year, month); } public static bool is_later_than(this YearMonth left, YearMonth right) { return left.CompareTo(right) > 0; } public static bool is_ealier_than(this YearMonth left, YearMonth right) { return left.CompareTo(right) < 0; } public static YearMonth get_ealier(this YearMonth left, YearMonth right) { if (left.is_ealier_than(right)) return left; return right; } public static YearMonth get_later(this YearMonth left, YearMonth right) { if (left.is_later_than(right)) return left; return right; }} |
[代码] 从测试看功能：公用的测试基类，很简单，就是声明一个YearMonth对象做测试
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public class YearMonthSpecs { protected static YearMonth subject; } |
[代码] 通过构造器，创建YearMonth对象
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public class When_init_by_year_month :YearMonthSpecs { private Because of = () => subject = new YearMonth(2011,3); private It year_should_set_properly = () => subject.Year.ShouldEqual(2011); private It month_should_set_properly = () => subject.Month.ShouldEqual(3); } |
[代码] 通过流畅接口创建YearMonth: 2012.year(3)。你还可以自己定制为: 2012.年(3)
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public class When_create_year_month_through_fluent_interface { private It should_create_year_month_properly = () => 2012.year(3).ShouldEqual(new YearMonth(2012, 3)); } |
[代码] 通过字符串创建
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public class When_init_by_string : YearMonthSpecs { private Because of = () => subject = new YearMonth("2011年01月"); private It year_should_set_properly = () => { subject.Year.ShouldEqual(2011); subject.Month.ShouldEqual(1); }; } |
[代码] Special Case模式，特别处理：世界末日的下一个月还是世界末日，创世纪的上一个月还是创世纪
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private It far_past_last_month_is_still_far_past = () => YearMonth.FarPast.get_last().ShouldEqual(YearMonth.FarPast); private It far_past_next_month_is_still_far_past = () => YearMonth.FarPast.get_next().ShouldEqual(YearMonth.FarPast); private It far_future_last_month_is_stil_far_future = () => YearMonth.FarFuture.get_last().ShouldEqual(YearMonth.FarFuture); private It far_future_next_month_is_stil_far_future = () => YearMonth.FarFuture.get_next().ShouldEqual(YearMonth.FarFuture); |
YearMonth结构类型的完整代码
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using System;using Skight.Arch.Domain.Interfaces;namespace Skight.Arch.Domain.Entities{ public struct YearMonth : IEquatable<YearMonth>, IComparable<YearMonth> { private readonly int ticks; private readonly int year; private readonly int month; private const int MONTHS_PER_YEAR=12; public static YearMonth FarPast = new YearMonth(0,1); public static YearMonth FarFuture = new YearMonth(9999,12); #region Constructors by ticks, year/month and datetime internal YearMonth(int ticks) { this.ticks = ticks; int remain; year = Math.DivRem(ticks-1, MONTHS_PER_YEAR, out remain); month = remain + 1; } public YearMonth(int year, int month) :this(year*MONTHS_PER_YEAR + month){} public YearMonth(DateTime date_time) :this(date_time.Year,date_time.Month){} public YearMonth(string yearMonth):this(int.Parse(yearMonth.Substring(0, 4)) ,int.Parse(yearMonth.Substring(5, 2))) {} #endregion public int Year { get { return year; } } public int Month { get { return month; } } public DateTime as_date_Time() { return new DateTime(Year,Month,1); } public override string ToString() { return string.Format("{0}年{1}月", year.ToString("0000"), month.ToString("00")); } #region Euqals and Compare public bool Equals(YearMonth other) { return other.ticks == ticks; } public override bool Equals(object obj) { if (ReferenceEquals(null, obj)) return false; if (obj.GetType() != typeof (YearMonth)) return false; return Equals((YearMonth) obj); } public override int GetHashCode() { return ticks; } public int CompareTo(YearMonth other) { return ticks.CompareTo(other.ticks); } #endregion #region Discrete interface public YearMonth get_last() { if (Equals(FarPast)) return FarPast; if (Equals(FarFuture)) return FarFuture; return new YearMonth(ticks - 1); } public YearMonth get_last(int Dvalue) { if (Equals(FarPast)) return FarPast; if (Equals(FarFuture)) return FarFuture; return new YearMonth(ticks - Dvalue); } public YearMonth get_next() { if (Equals(FarPast)) return FarPast; if (Equals(FarFuture)) return FarFuture; return new YearMonth(ticks + 1); } public YearMonth get_next(int DValue) { if (Equals(FarPast)) return FarPast; if (Equals(FarFuture)) return FarFuture; return new YearMonth(ticks + DValue); } #endregion public static implicit operator DateTime(YearMonth year_month) { return year_month.as_date_Time(); } public static implicit operator YearMonth(DateTime date_time) { return new YearMonth(date_time); } }} |