c# - Automapper 中参数的条件映射

Question

我想将一个参数传递给一个映射，然后它根据该参数决定一个值。

一个简单的类

public class Person
{
  string Name;
}

及其DTO

public class PersonDTO
{
  string Name;
  string IsAProgrammer;
}

我想要这样的东西

var parameterIsTrue = true; // how do I pass this value?

CreateMap<MyClassDTO, MyClass>()
  .ForMember(x => x.Name, opt => opt.MapFrom(src => src.Name))
  .ForMember(x => x.IsAProgrammer, 
               opt => opt.MapFrom(parameterIsTrue ? "sure!" : "nope"));

编辑

我正在尝试编写一个自定义解析器，但不知道如何向它传递参数。我想出了如何制作解析器:

public class PersonResolver : IValueResolver<Person, PersonDTO, string>
{
  ...
  public string Resolve(Person src, 
                        PersonDTO dest, 
                        string destMember, 
                        ResolutionContext context)
  {
    return (bool) context.Items["isProgrammer"] ? "sure!" : "nope";
  }
}

但我仍然无法映射:

CreateMap<MyClassDTO, MyClass>()
  .ForMember(x => x.Name, opt => opt.MapFrom(src => src.Name))
  .ForMember(x => x.IsAProgrammer, 
               opt => opt.ResolveUsing(PersonResolver)); // what ???
               // how do I pass the context?

Answer 1

我找到了适用于我的用例的解决方案。我有关于在某些情况下不想加载的对象的详细信息。

我创建了这个扩展方法，以便于对满足此条件的所有属性进行重用:

/// <summary>
/// Don't map the field if the provided <paramref name="keyName"/> is set to <see cref="false"/>. Defaults to true otherwise
/// </summary>
public static IMemberConfigurationExpression<TSource, TDestination, TMember> 
  IgnoreIfParam<TSource, TDestination, TMember>(
    this IMemberConfigurationExpression<TSource, TDestination, TMember> config, 
    string keyName)
{
    config
        .PreCondition(rc =>
        {
            if (rc.Options.Items.TryGetValue(keyName, out var performMapping) && performMapping is bool b)
            {
                return b;
            }
            return true;
        });
    return config;
}

在你的映射配置文件中，你可以像这样使用上面的扩展方法:

public const string IncludeDetail = "IncludeDetail";

public MyProfile() {
 CrateMap<Source, Dest>()
    //for a member with a specified MapFrom():
    .ForMember(x => x.Media, c => c.IgnoreIfParam(IncludeProductDetail).MapFrom(x => x.Detail.Media))
    
    //for a member with implied MapFrom() on the source, you don't need MapFrom()
    .ForMember(x => x.Name, c => c.IgnoreIfParam(MyProfile.IncludeDetail))

然后为了在映射时设置这个条件，我创建了另一个辅助扩展方法:

public static IMappingOperationOptions<object, TDestination> 
  SetOption<TDestination>(
    this IMappingOperationOptions<object, TDestination> options, 
    string key, bool val)
{
    options.Items[key] = val;
    return options;
}

然后你可以像这样在映射时调用它:

var res = _mapper.Map<MyView>(model, o => o
    .SetOption(MyProfile.IncludeDetail, false)
);
return res;