Do i need to create automapper createmap both ways

问题:

This might be a stupid question! (n00b to AutoMapper and time-short!)

I want to use AutoMapper to map from EF4 entities to ViewModel classes.

1) If I call

CreateMap<ModelClass, ViewModelClass>()

then do I also need to call

CreateMap<ViewModelClass, ModelClass>()

to perform the reverse?

2) If two classes have the same property names, then do I need a CreateMap statement at all, or is this just for "specific/custom" mappings?

回答1:

In AutoMapper you have a Source type and a Destination type. So you will be able to map between this Source type and Destination type only if you have a corresponding CreateMap. So to answer your questions:

1. You don't need to define the reverse mapping. You have to do it only if you intend to map back.
2. Yes, you need to call CreateMap to indicate that those types are mappable otherwise an exception will be thrown when you call Map<TSource, TDest> telling you that a mapping doesn't exist between the source and destination type.

回答2:

For the info of the people who stumble upon this question. There appears to be now a built-in way to achieve a reverse mapping by adding a .ReverseMap() call at the end of your CreateMap() configuration chain.

回答3:

I've used an extension method do mapping both ways

    public static IMappingExpression<TDestination, TSource> BothWays<TSource, TDestination>
        (this IMappingExpression<TSource, TDestination> mappingExpression)
    {
        return Mapper.CreateMap<TDestination, TSource>();
    }

usage:

 CreateMap<Source, Dest>().BothWays();