ViewModel attributes always null when posted - asp.net-mvc-4

Question

I have the following ViewModel
public class EditPatientViewModel
{
public Domain.Entities.Patient patient;
public IEnumerable<Espece> Especes;
public IEnumerable<Client> Clients;
}
the following controller
public ViewResult Edit(int Id_pat)
{
var ViewModel = new EditPatientViewModel();
ViewModel.patient = patientRepo.GetPatientById(Id_pat);
ViewModel.Especes = especeRepo.Especes;
return View(ViewModel);
}
[HttpPost]
public ActionResult Edit(EditPatientViewModel editPatientViewModel)
{
if (ModelState.IsValid)
{
patientRepo.Save(editPatientViewModel.patient);
TempData["message"] = "Sauvé";
return RedirectToAction("Index");
}
else
{
return View(editPatientViewModel);
}
}
and the following view
#model Veto.Models.ViewModels.EditPatientViewModel
#{
ViewBag.Title = "Edit";
}
<h2>Edit</h2>
#using (Html.BeginForm())
{
#Html.AntiForgeryToken()
<div class="form-horizontal">
<h4>Edit Patient</h4>
<hr />
#Html.ValidationSummary(true)
<div class="form-group">
<div class="col-md-10">
#Html.HiddenFor(m => m.patient.Id_pat)
</div>
</div>
<div class="form-group">
<div class="col-md-10">
#Html.EditorFor(m => m.patient.Nom_pat)
</div>
</div>
<div class="form-group">
<div class="col-md-offset-2 col-md-10">
<input type="submit" value="Save" class="btn btn-default" />
</div>
</div>
</div>
}
<div>
#Html.ActionLink("Back to List", "Index")
</div>
#section Scripts {
#Scripts.Render("~/bundles/jqueryval")
}
Every time I submit the form the ViewModel posted is not null but attributes are.. I would like to retrieve the attributes to make an update.
Why?
Tx,

Answer 1

Two same problem in one hour :)
Change your ViewModel to this:
public class EditPatientViewModel
{
public Domain.Entities.Patient patient { get; set; }
public IEnumerable<Espece> Especes { get; set; }
public IEnumerable<Client> Clients { get; set; }
}
In complex types, mvc model binder search for properties not for member variables.