mapping - 使用 Automapper 忽略具有默认值的映射属性

Question

我使用 Automapper 将对象源映射到对象目标。有什么方法可以仅将具有非默认值的属性从源对象映射到目标对象吗？

Answer 1

关键点是仅在满足这些条件时才检查源属性的类型和映射(对于引用类型，!= null；对于值，!= default类型):

Mapper.CreateMap<Src, Dest>()
    .ForAllMembers(opt => opt.Condition(
        context => (context.SourceType.IsClass && !context.IsSourceValueNull)
            || ( context.SourceType.IsValueType
                 && !context.SourceValue.Equals(Activator.CreateInstance(context.SourceType))
                )));

完整的解决方案是:

public class Src
{
    public int V1 { get; set; }
    public int V2 { get; set; }
    public CustomClass R1 { get; set; }
    public CustomClass R2 { get; set; }
}

public class Dest
{
    public int V1 { get; set; }
    public int V2 { get; set; }
    public CustomClass R1 { get; set; }
    public CustomClass R2 { get; set; }
}

public class CustomClass
{
    public CustomClass(string id) { Id = id; }

    public string Id { get; set; }
}

[Test]
public void IgnorePropertiesWithDefaultValue_Test()
{
    Mapper.CreateMap<Src, Dest>()
        .ForAllMembers(opt => opt.Condition(
            context => (context.SourceType.IsClass && !context.IsSourceValueNull)
                || ( context.SourceType.IsValueType
                     && !context.SourceValue.Equals(Activator.CreateInstance(context.SourceType))
                    )));

    var src = new Src();
    src.V2 = 42;
    src.R2 = new CustomClass("src obj");

    var dest = new Dest();
    dest.V1 = 1;
    dest.R1 = new CustomClass("dest obj");

    Mapper.Map(src, dest);

    //not mapped because of null/default value in src
    Assert.AreEqual(1, dest.V1);
    Assert.AreEqual("dest obj", dest.R1.Id);

    //mapped 
    Assert.AreEqual(42, dest.V2);
    Assert.AreEqual("src obj", dest.R2.Id);
}