什么是DDD
2 实现值对象值对象有两个主要特征：它们没有任何标识。它们是不可变的。
我们举个例子：小明是“浙江宁波”人，小红也是“浙江宁波”人，小王是“浙江杭州”人，在这个例子中，我们把地址可以独立出一个值对象出来，我们会遇到了多个对象是否相同的问题，例如小明和小红的地址应该是相等，小明和小王应该是不相等，这很好理解，我们来看一下例子；
public class Address { public string Province; public string City; } var xm = new Address { Province = "浙江", City = "宁波" }; var xh = new Address { Province = "浙江", City = "宁波" }; var xw = new Address { Province = "浙江", City = "杭州" }; Console.WriteLine(xm.Equals(xh)); Console.WriteLine(xm.Equals(xw));让我们来看看输出结果:
False False这个显然不符合我们预期，我们需要重写一下Equals，确保地址值相等的情况下对象相等。
public class Address { public string Province; public string City; public bool Equals(Address obj) { return this.Province.Equals(obj.Province) && this.City.Equals(obj.City); } } var xm = new Address { Province = "浙江", City = "宁波" }; var xh = new Address { Province = "浙江", City = "宁波" }; var xw = new Address { Province = "浙江", City = "杭州" }; Console.WriteLine(xm.Equals(xh)); Console.WriteLine(xm.Equals(xw));让我们来看看输出结果:
True False这个显然符合我们预期了，接下来我们把值对象的Equals方法封装到基类中。
public abstract class ValueObject { protected abstract IEnumerable<object> GetEqualityComponents(); public override bool Equals(object obj) { if (obj == null || obj.GetType() != GetType()) { return false; } var other = (ValueObject)obj; return this.GetEqualityComponents().SequenceEqual(other.GetEqualityComponents()); } } public class Address : ValueObject { public string Province; public string City; protected override IEnumerable<object> GetEqualityComponents() { yield return Province; yield return City; } } 3 实现实体实体主要特征：具有唯一标识。
前面我们讲到值对象将特定值都相等的对象视为相等对象，在实体中比较容易理解，标识相等的对象视为相等对象。
public abstract class Entity { #region IEntity Members public abstract Guid Id { get; set; } #endregion public override bool Equals(object obj) { if (obj == null || !(obj is Entity)) return false; if (Object.ReferenceEquals(this, obj)) return true; if (this.GetType() != obj.GetType()) return false; Entity item = (Entity)obj; return item.Id == this.Id; } public override int GetHashCode() { return base.GetHashCode(); } } 4 实现聚合根聚合根与实体的区别，实体只在聚合内部进行操作，聚合根是对外打交道的唯一实体。我们在这里设计时聚合根需要有增改删状态字段。
public enum AggregateState { Added = 1, Updated = 2, Deleted = 3 } public abstract class AggregateRoot : Entity { #region IAggregateRoot Members public AggregateState AggregateState { set; get; } #endregion }