使用 Automapper 将实体框架类映射到业务类

Question

I have the following two classes generated by Entity Framework:

public partial class Person
{
    public int id { get; set; }
    public string namen { get; set; }
    public int house { get; set; }
    [IgnoreMap]
    public virtual House House1 { get; set; }
}

public partial class House
{
    public House()
    {
        this.Persons = new HashSet<Person>();
    }
    public int id { get; set; }
    public string street { get; set; }
    public string city { get; set; }
    public ICollection<Person> Persons { get; set; }
}

Then I also have these two similar classes in my Business Layer:

public class House
{        
    public House()
    {
        this.Persons = new HashSet<Person>();
    }
    public int id { get; set; }
    public string street { get; set; }
    public string city { get; set; }        
    public virtual ICollection<Person> Persons { get; set; }
}

public class Person
{
    public int id { get; set; }
    public string namen { get; set; }
    public int house { get; set; }        
}

Pretty much the same, hugh? In my Business Layer I read a List of houses from the Database. Then I map the whole list to a list of my Business house class using Automapper:

    public List<elci.BusinessEntities.House> getHouses()
    {
        YardEntities cx = new YardEntities();
        Mapper.Initialize(cfg => cfg.CreateMap<DataAccessLayer.House, BusinessEntities.House>());

        List<DataAccessLayer.House> dhl = cx.Houses.ToList();
        List<BusinessEntities.House> bhl = Mapper.Map<List<DataAccessLayer.House>, List<BusinessEntities.House>>(dhl);
        return bhl;
    }

However, in the following line I get a runtime exception:

 Mapper.Map<List<DataAccessLayer.House>, List<BusinessEntities.House>>(dhl);

"Error mapping types".

I guess, that this might be, because every Person points to a House and every House points to Persons. Because I do not need this "circle" in my BusinessLayer I decorated this attribute with [IgnoreMap], but without any success. The error still remains.

Any suggest what I am doing wrong?

Answer 1

So this eventually fixed my issue:

        Mapper.Initialize(cfg => {
            cfg.CreateMap<List<House>, List<HouseViewModel>>();
            cfg.CreateMap<List<Person>, List<PersonViewModel>>();
        });

Answer 2

Yes, the error remains without ignoremap. The inner exception tells me the following:

{"Error mapping types.\r\n\r\nMapping types:\r\nList`1 -> List`1\r\nSystem.Collections.Generic.List`1[[elci.DataAccessLayer.House, DataAccessLayer, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]] -> System.Collections.Generic.List`1[[elci.BusinessEntities.House, BusinessEntities, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]]"}

So the House-Type is the problem. I also tried to add another map:

        Mapper.Initialize(cfg => cfg.CreateMap<DataAccessLayer.House, BusinessEntities.House>());
        Mapper.Initialize(cfg => cfg.CreateMap<DataAccessLayer.Person, BusinessEntities.Person>());

without success and the same error. :-(

Answer 3

Try to use

config.CreateMap<TSource,TDestination>().PreserveReferences()

You have circular references Person->House->ICollection

Circular references

Previously, AutoMapper could handle circular references by keeping track of what was mapped, and on every mapping, check a local hashtable of source/destination objects to see if the item was already mapped. It turns out this tracking is very expensive, and you need to opt-in using PreserveReferences for circular maps to work. Alternatively, you can configure MaxDepth:

// Self-referential mapping
cfg.CreateMap<Category, CategoryDto>().MaxDepth(3);
// Circular references between users and groups
cfg.CreateMap<User, UserDto>().PreserveReferences();

AutoMapper docs