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
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
public class YearMonthSpecs
{
protected static YearMonth subject;
}
[代码] 通过构造器，创建YearMonth对象
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)
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
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
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
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);
}
}
}
皓月碧空,漫野如洗,行往卓越的路上
