Validation model always fails

Question

I have the following models:

public class Local {
    [Key]
    public int Id { get; set; }

    public virtual Grupo Grupo { get; set; }
 }

public class Grupo
{
    [Key]
    public int Id { get; set; }

    [Required]
    public int? LocalId { get; set; }

    [Required]
    [StringLength(60)]
    public string Nome { get; set; }

    [ForeignKey("LocalId")]
    public virtual Local Local { get; set; }
}

In my controller before validating the model and adding to the database I inform the id of Local through a Session.

    [HttpPost]
    [ValidateAntiForgeryToken]
    public virtual ActionResult _Create(Grupo model)
    {
        model.LocalId = SessionContext.LocalSelecionado;

        if (ModelState.IsValid)
        {
            _service.Add(model);
            return RedirectToAction("_List");
        }

        return PartialView(model);
    }

Every time the validation fails saying that the LocalId is mandatory, and is, but I’m putting the value, at the breakpoint if I look at the locals of model is there the value and yet fails.

The only way I could do it is in the form by putting a field with name LocalId and bringing the value of the form so it also continues to recognize and the validation does not fail.

What can it be?

Answer 1

You can use the following method: Modelstate.Clear(); to clean the model state and re-run the Modelstate.Isvalid.

Modelstate.Clear() performs a revalidation based on the currently populated model, already with its changes after sending the form, already in Action. Your method would look like this:

[HttpPost]
[ValidateAntiForgeryToken]
public virtual ActionResult _Create(Grupo model)
{
    model.LocalId = SessionContext.LocalSelecionado;

    ModelState.Clear();

    if (ModelState.IsValid)
    {
        _service.Add(model);
        return RedirectToAction("_List");
    }

    return PartialView(model);
}

Answer 2

This is because the Model is only validated before the Controller is executed, changing the model’s value will not change the value of the ModelState.IsValid

In your case you could take the [Required] of LocalId since it is not required to fill in this field by the user, it will be filled in by your program.