如何设计与复杂的初始化不可变对象 [英] How to design an immutable object with complex initialization

问题描述

我了解DDD和所遇到的声明说：值对象应该是一成不变的。据我所知，这意味着它已经被创建后的对象状态应该不会改变。这是怎么样的思考我的新方式，但它是有道理的在许多情况下。

I'm learning about DDD, and have come across the statement that "value-objects" should be immutable. I understand that this means that the objects state should not change after it has been created. This is kind of a new way of thinking for me, but it makes sense in many cases.

好了，我开始创建不可变的值对象。

Ok, so I start creating immutable value-objects.

• 我要确保他们采取了整个状态参数的构造函数，


• 我不不要再增加属性setter，


• 并确保没有方法允许修改内容（只返回新的实例）。

但现在我想创建该值对象将包含8种不同的数值。如果我创建具有8个数字参数我觉得这不会是很容易使用，或者更确切地说，构造 - 它会很容易传入数字时犯了一个错误。这不可能是好的设计

But now I want to create this value object that will contain 8 different numeric values. If I create a constructor having 8 numeric parameters I feel that it will not be very easy to use, or rather - it will be easy to make a mistake when passing in the numbers. This can't be good design.

的所以，问题是：的有没有让我不可变对象更好的其他任何方式..，任何魔法，可以在C＃来完成，以克服在构造一个长参数列表？我在听你的想法。

So the questions is: Are there any other ways of making my immutable object better.., any magic that can be done in C# to overcome a long parameter list in the constructor? I'm very interested in hearing your ideas..

更新很感兴趣：之前有人提到它，一个想法已经在这里讨论：
http://stackoverflow.com/questions/263585/immutable -object图案，在C-什么-DO-你思考

UPDATE: Before anyone mentions it, one idea has been discussed here: http://stackoverflow.com/questions/263585/immutable-object-pattern-in-c-what-do-you-think

是否有兴趣听取其他建议或意见，虽然。

Would be interested in hearing other suggestions or comments though.

推荐答案

使用一个生成器：

public class Entity
{
   public class Builder
   {
     private int _field1;
     private int _field2;
     private int _field3;

     public Builder WithField1(int value) { _field1 = value; return this; }
     public Builder WithField2(int value) { _field2 = value; return this; }
     public Builder WithField3(int value) { _field3 = value; return this; }

     public Entity Build() { return new Entity(_field1, _field2, _field3); }
   }

   private int _field1;
   private int _field2;
   private int _field3;

   private Entity(int field1, int field2, int field3) 
   {
     // Set the fields.
   }

   public int Field1 { get { return _field1; } }
   public int Field2 { get { return _field2; } }
   public int Field3 { get { return _field3; } }

   public static Builder Build() { return new Builder(); }
}

然后创建它喜欢的：

Then create it like:

Entity myEntity = Entity.Build()
                   .WithField1(123)
                   .WithField2(456)
                   .WithField3(789)
                  .Build()

如果某些参数都是可选的，你不会需要调用该WithXXX方法，它们可以有默认值。

If some of the parameters are optional you won't need to call the WithXXX method and they can have default values.

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