Problems saving a selected item in Dropdownlistfor using a Viewmodel

Question

I’m trying to save a change I try to make by selecting a Category in a Dropdownlistfor.

Kind of:

I keep following the Debug and the View is sending the selected Category, but I am not able to continue this change.

My Subcategory Controller looks like this:

 // GET: SubCategorias/Edit/5
    public ActionResult Edit(Guid? id)
    {
        if (id == null)
            return new HttpStatusCodeResult(HttpStatusCode.BadRequest);

        SubCategoriaViewModel subCategoriaViewModel =
            _subCategoriaAppService.ObterPorId(id.Value);

        subCategoriaViewModel.Categorias = _categoriaAppService.ObterTodas();

        if (subCategoriaViewModel == null)
            return HttpNotFound();

        return View(subCategoriaViewModel);
    }

    // POST: SubCategorias/Edit/5
    [HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult Edit(SubCategoriaViewModel subCategoriaViewModel)
    {            
        _subCategoriaAppService.Atualizar(subCategoriaViewModel);
        return RedirectToAction("Index");
    }

My method for upgrading is like this:

public SubCategoriaViewModel Atualizar(
        SubCategoriaViewModel subCategoriaViewModel)
    {
        //var categoriaSelecionada =
        //     _categoriaService.ObterPorId(subCategoriaViewModel.CategoriaId);
        subCategoriaViewModel.Categoria =
            _categoriaService.ObterPorId(subCategoriaViewModel.CategoriaId);

        var subCategoria =
            Mapper.Map<SubCategoriaViewModel,
            SubCategoria>(subCategoriaViewModel);

        //subCategoria.Categoria = categoriaSelecionada;
        _subCategoriaService.Atualizar(subCategoria);

        return subCategoriaViewModel;
    }

In my View:

<div class="form-group">
        @Html.LabelFor(model => model.Categoria, htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.DropDownListFor(model => model.CategoriaId,
           new SelectList(Model.Categorias, "CategoriaId", "CategoriaNome"), new { @class = "form-control" })              
        </div>
    </div>

My Viewmodel

public class SubCategoriaViewModel
{
    public SubCategoriaViewModel()
    {
        SubCategoriaId = Guid.NewGuid();
    }

    [Key]
    public Guid SubCategoriaId { get; set; }

    [Required(ErrorMessage = ("Preencha o nome da SubCategoria."))]
    [MaxLength(60, ErrorMessage = ("Máximo {0} caracteres."))]
    [MinLength(1, ErrorMessage = ("Mínimo {0} caracteres."))]
    [DisplayName("Nome")]
    public string SubCategoriaNome { get; set; }

    public IEnumerable<CategoriaViewModel> Categorias = new List<CategoriaViewModel>();
    public Guid CategoriaId { get; set; }

    //[ScaffoldColumn(false)]
    //public DomainValidation.Validation.ValidationResult ValidationResult { get; set; }

    public virtual Categoria Categoria { get; set; }
    //public ICollection<Produto> Produtos { get; set; }

}

The interesting thing is that if I modify the name of the subcategory it persisted! Anything, this the way I’m trying to persist this http://imgur.com/a/i75n3

Answer 1

After much conversation with two good people at heart (Tiago Silva and LP. Gonçalves), we can understand the problem.

The problem was how I was treating the Association Type to save and/or change my entities in the database using the Entity Framework.

Before the solution, I was using Associação Independente which was one of the first forms of association between entities and which used object orientation to make this association. As you may already know, I was misusing the resource. So in conversation with Tiago Silva he explained me the error and why it would be better to use Foreign key association (Foreign Key).

What has changed is my application class, which is now like this:

public SubCategoriaViewModel Atualizar(
        SubCategoriaViewModel subCategoriaViewModel)
    {
        var categoriaSelecionada =
             _categoriaService.ObterPorId(subCategoriaViewModel.CategoriaId);

        var subCategoria =
            Mapper.Map<SubCategoriaViewModel,
            SubCategoria>(subCategoriaViewModel);

        subCategoria.Categoria = categoriaSelecionada;
        _subCategoriaService.Atualizar(subCategoria);

        return subCategoriaViewModel;
    }

And, there was the addition of property public Guid CategoriaId { get; set; } in the Subcategory domain class, to serve as a foreign key in the Category-Subcategory association (1:N). Follows the code:

public class SubCategoria
{
    public Guid SubCategoriaId { get; set; }
    public string SubCategoriaNome { get; set; }
    public virtual Categoria Categoria { get; set; }
    public Guid CategoriaId { get; set; }
    public ICollection<Produto> Produtos { get; set; }

    public SubCategoria()
    {
        SubCategoriaId = Guid.NewGuid();
        Produtos = new List<Produto>();
    }        
}

Who wants to take a look at the material I read on the topic, follow the links

• Foreign Key and Independent Association in the Entity Framework
• Foreign key and Independent Associations in the Entity Framework (en)
• Foreign Key and Independent Association in the Entity Framework

Answer 2

If I understand your problem well, the solution is very simple, just fill in the CategoriaId before calling the view.

Yeah, how do you know, CategoriaId is responsible for the value of the selected object in the dropdown, if you do not initialize this variable with the correct value, the dropdown will be displayed the option default which in its case is the first object of the list of Categorias.

The solution to your problem is:

subCategoriaViewModel.CategoriaId = Id.value; 

I don’t understand your structure, but it’s the id of the category you saved in the comic.