Net中有一個DateTime結構類，涉及時間和日期，這個類大量使用。可是，他的名稱已經顯著的表明他是表達某個具體的時刻。當我們不需要每天的具體時間時，如：我的程序邏輯僅僅需要年月（發工資的周期？），這個DateTime顯得有些累贅，甚至不合用。
一般人們解決的方式，仍然使用DateTime而從數據上，設置hour,mintue等等為0。 然而，這與DDD的理念相背，名稱有與含義有偏差，另外，數據一致性的維護，散布在各個角落，如，保證日期始終為1，小時，分鍾為0。另外，與月份相關的功能，如：得到下一個月份，要么用DateTime本身的功能（AddMonths),要么提煉出一個Utitlies出來。 前者，需要開發者時刻重復DateTime到YearMonth的映射邏輯，后者是個反模式。 （本文版權屬於© 2012 - 2013 予沁安）
這里，我創建出一個基本類型YearMonth，可以作為代碼的基本磚塊。
[代碼] 用Extension的方式，來增強代碼流暢性和可讀性
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;
}
}
[代碼] 從測試看功能：公用的測試基類，很簡單，就是聲明一個YearMonth對象做測試
public class YearMonthSpecs
{
protected static YearMonth subject;
}
[代碼] 通過構造器，創建YearMonth對象
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);
}
[代碼] 通過流暢接口創建YearMonth: 2012.year(3)。你還可以自己定制為: 2012.年(3)
public class When_create_year_month_through_fluent_interface
{
private It should_create_year_month_properly =
() => 2012.year(3).ShouldEqual(new YearMonth(2012, 3));
}
[代碼] 通過字符串創建
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);
};
}
[代碼] Special Case模式，特別處理：世界末日的下一個月還是世界末日，創世紀的上一個月還是創世紀
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結構類型的完整代碼
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);
}
}
}