How to make Optimistic Concurrency editing in Asp.net mvc 3 without using hiddenfields in the view? - asp.net-mvc-3

Question

I'm studying asp.net mvc 3 right now and I'm following this tutorial Contoso University
http://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/handling-concurrency-with-the-entity-framework-in-an-asp-net-mvc-application
I'm in this part where editing a model is handled with Optimistic Concurrency
I'm aware that by using something like
[HttpPost]
public ActionResult Edit(Department department)
the model will automatically be binded, even without a hidden field for the id of the department to be edited, and the edit will not fail.
But whenever I try to remove the two hiddenfields in the view of this one:
#model MvcContosoUniversity.Models.Department
#{
ViewBag.Title = "Edit";
}
<h2>Edit</h2>
<script src="#Url.Content("~/Scripts/jquery.validate.min.js")" type="text/javascript"></script>
<script src="#Url.Content("~/Scripts/jquery.validate.unobtrusive.min.js")" type="text/javascript"></script>
#using (Html.BeginForm()) {
#Html.ValidationSummary(true)
<fieldset>
<legend>Department</legend>
#Html.HiddenFor(model => model.DepartmentID)
#Html.HiddenFor(model => model.Timestamp)
<div class="editor-label">
#Html.LabelFor(model => model.Name)
</div>
<div class="editor-field">
#Html.EditorFor(model => model.Name)
#Html.ValidationMessageFor(model => model.Name)
</div>
<div class="editor-label">
#Html.LabelFor(model => model.Budget)
</div>
<div class="editor-field">
#Html.EditorFor(model => model.Budget)
#Html.ValidationMessageFor(model => model.Budget)
</div>
<div class="editor-label">
#Html.LabelFor(model => model.StartDate)
</div>
<div class="editor-field">
#Html.EditorFor(model => model.StartDate)
#Html.ValidationMessageFor(model => model.StartDate)
</div>
<div class="editor-label">
#Html.LabelFor(model => model.InstructorID, "Administrator")
</div>
<div class="editor-field">
#Html.DropDownList("InstructorID", String.Empty)
#Html.ValidationMessageFor(model => model.InstructorID)
</div>
<p>
<input type="submit" value="Save" />
</p>
</fieldset>
}
<div>
#Html.ActionLink("Back to List", "Index")
</div>
I get an error in the controller, here's the code for the controller:
// GET: /Department/Edit/5
public ActionResult Edit(int id)
{
Department department = db.Departments.Find(id);
ViewBag.InstructorID = new SelectList(db.Instructors, "InstructorID", "FullName", department.InstructorID);
return View(department);
}
//
// POST: /Department/Edit/5
[HttpPost]
public ActionResult Edit(Department department)
{
try
{
if (ModelState.IsValid)
{
db.Entry(department).State = EntityState.Modified;
db.SaveChanges();
return RedirectToAction("Index");
}
}
catch (DbUpdateConcurrencyException ex)
{
var entry = ex.Entries.Single();
//Another option is to put the try-catch inside a function
try
{
var databaseValues = (Department)entry.GetDatabaseValues().ToObject();
var clientValues = (Department)entry.Entity;
if (databaseValues.Name != clientValues.Name)
ModelState.AddModelError("Name", "Current value: "
+ databaseValues.Name);
if (databaseValues.Budget != clientValues.Budget)
ModelState.AddModelError("Budget", "Current value: "
+ String.Format("{0:c}", databaseValues.Budget));
if (databaseValues.StartDate != clientValues.StartDate)
ModelState.AddModelError("StartDate", "Current value: "
+ String.Format("{0:d}", databaseValues.StartDate));
if (databaseValues.InstructorID != clientValues.InstructorID)
ModelState.AddModelError("InstructorID", "Current value: "
+ db.Instructors.Find(databaseValues.InstructorID).FullName);
ModelState.AddModelError(string.Empty, "The record you attempted to edit "
+ "was modified by another user after you got the original value. The "
+ "edit operation was canceled and the current values in the database "
+ "have been displayed. If you still want to edit this record, click "
+ "the Save button again. Otherwise click the Back to List hyperlink.");
department.Timestamp = databaseValues.Timestamp;
}
catch(NullReferenceException e)
{
ModelState.AddModelError("","Error \n "+e.Message);
}
}
catch (DataException)
{
//Log the error (add a variable name after Exception)
ModelState.AddModelError(string.Empty, "Unable to save changes. Try again, and if the problem persists contact your system administrator.");
}
ViewBag.InstructorID = new SelectList(db.Instructors, "InstructorID", "FullName", department.InstructorID);
return View(department);
}
Here is the code for the model:
public class Department
{
public int DepartmentID { get; set; }
[Required(ErrorMessage = "Department name is required.")]
[MaxLength(50)]
public string Name { get; set; }
[DisplayFormat(DataFormatString = "{0:c}")]
[Required(ErrorMessage = "Budget is required.")]
[Column(TypeName = "money")]
public decimal? Budget { get; set; }
[DisplayFormat(DataFormatString = "{0:d}", ApplyFormatInEditMode = true)]
[Required(ErrorMessage = "Start date is required.")]
public DateTime StartDate { get; set; }
[Display(Name = "Administrator")]
public int? InstructorID { get; set; }
public virtual Instructor Administrator { get; set; }
public virtual ICollection<Course> Courses { get; set; }
[Timestamp]
public Byte[] Timestamp { get; set; }
}
Is it possible to make it work without using hiddenfields?
Sir/Ma'am your answers would be of great help. Thank you++

Answer 1

You need to have the id value coming from somewhere, or that entity can't be saved... how does EF know what ID it's saving without it?
It doesn't have to be via hidden field; It's probably there in the query string from the initial GET request for the edit action.