如何不丢失是present我的目标对象，但不是在我的源对象使用AutoMapper映射后的属性 [英] How not to lose properties that are present in my destination object but are NOT in my source object after mapping using AutoMapper

问题描述

我有下面的类结构：

public class A
{
    public bool Property1 { get; set; }
    public bool Property2 { get; set; }
}

public class ContainerForA
{
    public A A { get; set; }
}

public class A1
{
    public bool Property1 { get; set; }
}

public class ContainerForA1
{
    public A1 A { get; set; }
}

我创建此组类的映射：

I create a mapping for this set of classes:

Mapper.CreateMap<A1, A>();
Mapper.CreateMap<ContainerForA1, ContainerForA>();

我创建这个组类的一个实例：

I create an instance of this set of classes:

        var cnt_a = new ContainerForA()
                        {
                            A = new A()
                                    {
                                        Property1 = false,
                                        Property2 = true
                                    }
                        };

        var cnt_a1 = new ContainerForA1()
                         {
                             A = new A1()
                                     {
                                         Property1 = true
                                     }
                         };

如果我称之为 Mapper.Map（cnt_a1.A，cnt_a.A）我得到的结果我期待：这两个属性（ Property1 和 Property2 对象）的 cnt_a 是真正

If I call Mapper.Map(cnt_a1.A, cnt_a.A) I'm getting the result I was expecting: both properties (Property1 and Property2) of object cnt_a are true

但是，如果我称之为 Mapper.Map（cnt_a1，cnt_a）我收到如此 Property1 和假为 Property2 。有人能解释我为什么？而没有任何选项，我宣布我的映射的方式，所以我不会失去的是present我的目标对象，但不是在我的源对象？属性

But if I call Mapper.Map(cnt_a1, cnt_a) I'm getting true for Property1 and false for Property2. Could someone explain me why? And is there any option for me to declare my mappings in the way so I won't lose properties that are present in my destination object but are NOT in my source object?

推荐答案

我猜想，当你从 ContainerForA1 映射到 ContainerForA ，当映射属性的，它 ContainerForA A 一个新实例>，而不是用现有之一。这将使用默认值，所有属性，这是假为布尔。

I would guess that when you map from ContainerForA1 to ContainerForA, that when mapping the property A, it creates a new instance of A for ContainerForA rather than using the existing one. This will use the default values for all of the properties, which is false for a bool.

我们如何解决此问题？

首先，我们需要告诉AutoMapper不覆盖的属性的上ContainerForA。为了做到这一点，我们会告诉AutoMapper忽略属性。

First, we need to tell AutoMapper to not overwrite the property A on ContainerForA. To do that, we will tell AutoMapper to ignore the property.

Mapper.CreateMap<ContainerForA1, ContainerForA>()
    .ForMember(cForA => cForA.A, option => option.Ignore());

现在，我们需要手动更新，使用AfterMap

Now we need to update A manually, using AfterMap

Mapper.CreateMap<ContainerForA1, ContainerForA>()
    .ForMember(cForA => cForA.A, option => option.Ignore())
    .AfterMap((cForA1, cForA) => Mapper.Map(cForA1.A, cForA.A));

您可能会想一些检查，添加到AfterMap方法，以确保cForA.A不为空。我会留给你。

You will probably want to add some checks to the AfterMap method to ensure that cForA.A is not null. I'll leave that for you.

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