AutoMapper:MapFrom和ResolveUsing有什么区别? [英] AutoMapper: What is the difference between MapFrom and ResolveUsing?

问题描述

忽略采用IValueResolver的ResolveUsing重载，仅查看以下两种方法:

Ignoring the ResolveUsing overloads that take an IValueResolver, and looking only at these 2 methods:

void ResolveUsing(Func<TSource, object> resolver);
void MapFrom<TMember>(Expression<Func<TSource, TMember>> sourceMember);

这2个之间的主要区别似乎是ResolveUsing带有Func<TSource, object>，而MapFrom带有Expression<Func<TSource, TMember>>.

The main difference between these 2 seems to be that ResolveUsing takes a Func<TSource, object>, whereas MapFrom takes an Expression<Func<TSource, TMember>>.

但是在实际使用以下方法之一和lambda表达式的客户端代码中，它们似乎是可互换的:

However in client code that actually uses one of these methods with a lambda expression, they seem to be interchangeable:

Mapper.CreateMap<SourceType, DestType>() // uses ResolveUsing
   .ForMember(d => d.DestPropX, o => o.ResolveUsing(s => s.SourcePropY));

Mapper.CreateMap<SourceType, DestType>() // uses MapFrom
   .ForMember(d => d.DestPropX, o => o.MapFrom(s => s.SourcePropY));

那么，以上两种选择之间的最终区别是什么?一个比另一个快吗?一个是比另一个更好的选择，如果是，何时/为什么?

So what ultimately is the difference between the above 2 choices? Is one faster than the other? Is one a better choice than the other and if so, when / why?

推荐答案

过去，我有一个在邮件列表上与Automapper的作者进行长时间的电子邮件交换. MapFrom将通过表达式一直执行空检查:

In the past I had a long email exchange on the mailing list with the author of Automapper. MapFrom will do null checks all the way trough the expression:

因此您可以执行opt => opt.MapFrom(src => src.SomeProp.Way.Down.Here.Somewhere)，每个级别都会被检查 为null(就像它已经为扁平化所做的那样.)

So you can do opt => opt.MapFrom(src => src.SomeProp.Way.Down.Here.Somewhere) and each level will get checked for nulls (as it already does for flattening).

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