Question

为什么这样做

Mapper.CreateMap<MyObject, AnotherObject>().
ForMember(x => x.DateAsString, m => m.ResolveUsing<StringToDateTimeFormatter>());

private class StringToDateTimeFormatter : ValueResolver<DateTime, string>
{
    protected override string ResolveCore(DateTimesource)
    {
        return source.ToString("yyyy-MM-dd");
    }

 }

何时可以这样做

Mapper.CreateMap<MyObject, AnotherObject>().
ForMember(x => x.DateAsString, m => m.MapFrom(x => x.Date.ToString("yyy-MM-dd")));

???

更新

以下是如何执行更复杂的业务逻辑的示例

Mapper.CreateMap<MyObject, AnotherObject>().
ForMember(x => x.DateAsString, m => m.MapFrom(n => MyMethod(n.DateAsString)));

    private object MyMethod(string dateTime)
    {
        if(!MyDomainObjectIsValid(dateTime))
        {
            throw new MyValidationException();
        }

        // do more stuff
    }

我仍然认为不需要ValueResolver ......

Answer 1

显然，对于您的示例，仅使用MapFrom更合理。更复杂的情况需要ValueResolvers。例如，当您需要进行一些验证并相应地抛出异常时。

修改 ValueResolvers提供对目标类型和值的访问。这是一个小例子。

public class FakeResolver : IValueResolver { public ResolutionResult Resolve(ResolutionResult source) { if (source.Context.DestinationType == typeof(string) && source.Context.DestinationValue == "test") throw new Exception(); return source; } }

为什么要使用Automapper ValueResolver？

1 个答案: