当源上的属性为假时是否可以映射到 null？

Question

我正在定义源 class 和目标 class 之间的映射：

Mapper.CreateMap<Source, Target>();

如果 Source 上的某个属性设置为特定值，我希望映射到 return null：

// If Source.IsValid = false I want the mapping to return null
Source s = new Source { IsValid = false };
Target t = Mapper.Map<Target>(s);
Assert.IsNull(t);

如何配置 AutoMapper 来实现？

Answer 1

编辑

如果你想让你的地图输出一个空对象，我建议使用两个级别的映射：第一级决定是否 return 一个空对象通过接管映射行为 ConvertUsing 方法，如果需要映射，它将它推迟到内部映射引擎：

static void Main(string[] args)
{
    var innerConfigurationStore = new ConfigurationStore(new TypeMapFactory(), MapperRegistry.Mappers);
    innerConfigurationStore.CreateMap<From, To>()
                .ForMember(to => to.DestinationName, opt => opt.MapFrom(from => from.Active ? from.Name : (string)null));
    var innerMappingEngine = new MappingEngine(innerConfigurationStore);

    Mapper.CreateMap<From, To>()
        .ConvertUsing(from => from.Active ? innerMappingEngine.Map<To>(from) : null)
        ;

    WriteMappedFrom(new From() {Active = true, Name = "ActiveFrom"});
    WriteMappedFrom(new From() {Active = false, Name = "InactiveFrom"});
}

static void WriteMappedFrom(From from)
{
    Console.WriteLine("Mapping from " + (from.Active ? "active" : "inactive") + " " + from.Name);
    var to = Mapper.Map<To>(from);
    Console.WriteLine("To -> " + (to == null ? "null" :  "not null"));
}

初始答案

在Automapper中使用条件映射非常简单，这里是一些示例代码

public class From
{
    public bool Active { get; set; }
    public string Name { get; set; }
}

public class To
{
    public string DestinationName { get; set; }
}
static void Main(string[] args)
{
    Mapper.CreateMap<From, To>()
        .ForMember(to => to.DestinationName, opt => opt.MapFrom(from => from.Active ? from.Name : (string)null));

    WriteMappedFrom(new From() {Active = true, Name = "ActiveFrom"});
    WriteMappedFrom(new From() {Active = false, Name = "InactiveFrom"});
}

static void WriteMappedFrom(From from)
{
    Console.WriteLine("Mapping from " + (from.Active ? "active" : "inactive") + " " + from.Name);
    var to = Mapper.Map<To>(from);
    Console.WriteLine("To -> " + (to.DestinationName ?? "null"));
}

automapper 中还有其他 conditional mappings，但它们似乎只适用于基于约定的映射。但是，您可以进一步查看文档以确认

Answer 2

您可以这样定义您的映射：

Mapper.CreateMap<Source, Target>().TypeMap
  .SetCondition(r => ((Source)r.SourceValue).IsValid);

当源上的属性为假时是否可以映射到 null？

Is it possible to map to null when a property on source is false?

.net

c#

automapper

当源上的 属性 为假时是否可以映射到 null？

Is it possible to map to null when a property on source is false?

.net

c#

automapper

当源上的属性为假时是否可以映射到 null？