Question

I’m trying to insert a new Entity in EF:

public class Ad
{
    // Primary properties
    public int Kms { get; set; }

    // Navigation properties
    public virtual Model Model { get; set; }
}

And I receive from the View the model like this (example values):

kms = 222
Model.Id = 3

Then when I do the Add and SaveChanges of the Entity Framework, I get a NULL record inserted in the Model Table (that generated a new ID) and a record in the Ad Table with the new inserted Model Id.

Why is this happening?

Service Layer:

    public void CreateAd(CreateAdDto adDto)
    {
        var adDomain = Mapper.Map<CreateAdDto, Ad>(adDto);

        _adRepository.Add(adDomain);
        _adRepository.Save();
    }

Repository:

    public void Add(T entity)
    {
        _dbSet.Add(entity);
    }

   public void Save()
    {
        try
        {
            _dataContext.SaveChanges();
        }
        catch (DbEntityValidationException e)
        {
            var s = e.EntityValidationErrors.ToList();
            throw;
        }
    }

ViewModel:

public class CreateAdViewModel
{
    // Primary properties
    public string Version { get; set; }
    public int Kms { get; set; }
    public int Year { get; set; }
    public decimal Price { get; set; }

    public int Make_Id { get; set; }
    public int Model_Id { get; set; }

    // Navigation properties
    public IEnumerable<SelectListItem> MakeList { get; set; }
    public IEnumerable<SelectListItem> ModelList { get; set; }
}

Dto:

public class CreateAdDto
{
    // Primary properties
    public int Kms { get; set; }
    public int Model_Id { get; set; }
}

The Mapping:

        Mapper.CreateMap<CreateAdDto, Ad>().ForMember(dest => dest.Model, opt => opt.MapFrom(src => new Model { Id = src.Model_Id }));

Answer 1

If you just call the Add method on the Ad instance, all the related entities are treated as new entities. Therefore you can attach the Model instance first and add the Ad.

context.Models.Attach(ad.Model);
context.Ads.Add(ad);
context.SaveChanges();