Entity Framework + AutoMapper ( Entity to DTO and DTO to Entity )

Answer 1

I'm not sure what your problem is, but - when i wanted to use LINQToEntities (switched to NHibernate),
i managed to use automapper with success.

Take a look at code:

public class SimpleMapper<TFrom, TTo>
{
    public static TTo Map(TFrom fromModel)
    {
        Mapper.CreateMap<TFrom, TTo>();
        return Mapper.Map<TFrom, TTo>(fromModel);
    }

    public static IList<TTo> MapList(IList<TFrom> fromModel)
    {
        Mapper.CreateMap<TFrom, TTo>();
        return Mapper.Map<IList<TFrom>, IList<TTo>>(fromModel);
    }
}

public class RepositoryBase<TModel, TLINQModel>
{
    public IList<TModel> Map<TCustom>(IList<TCustom> model)
    {
        return SimpleMapper<TCustom, TModel>.MapList(model);
    }

    public TModel Map(TLINQModel model)
    {
        return SimpleMapper<TLINQModel, TModel>.Map(model);
    }

    public TLINQModel Map(TModel model)
    {
        return SimpleMapper<TModel, TLINQModel>.Map(model);
    }

    public IList<TModel> Map(IList<TLINQModel> model)
    {
        return SimpleMapper<TLINQModel, TModel>.MapList(model);
    }

    public IList<TLINQModel> Map(IList<TModel> model)
    {
        return SimpleMapper<TModel, TLINQModel>.MapList(model);
    }
}

It's quite cryptic, always recreates mappings, but it worked. I hope it helps somehow. :)

Answer 2

AutoMapper is very expressive when it comes to mapping error. read the exception message carefully.

another important thing is to remember to call Mapper.AssertConfigurationIsValid(); after creating the mappings. it gives an error if the mapping is wrong, thus preventing an exception later in the application runtime.

Answer 3

Your problem is because Automapper loses the EntityKey associated with the record. As the EntityFramework does not by default handle POCO's (Plain Old CLR Object)

Jay Zimmerman has a good example here of how to handle this from is. gd /4NIcj Also from Jaroslaw Kowalski (part of the EF team I believe ) has this example for using POCO's within EF, which may translate well to use with Automapper (I've not yet had a chance to try it) : http://blogs.msdn.com/jkowalski/archive/2008/09/09/persistence-ignorance-poco-adapter-for-entity-framework-v1.aspx

Answer 4

The problem I had was related to updates to EntityCollection references. AutoMapper creates a new instance of the relation when mapping from the DTO to the Entity, and that doesn't please the EF.

What solved my problem was configuring AutoMapper to use the destination value for my EntityCollection properties. In your case:

Mapper.CreateMap< CustomerDTO , Customers >().ForMember(c => c.Orders, o => o.UseDestinationValue());

That way AM will not create a new EntityCollection instance, and will use that wich came with the original Customer entity.

I'm still working for a way to automate this, but for now it solves my problem.