Parameter for "Delete" post method has blank attributes in ASP.NET MVC - asp.net-mvc

Question

I'm having an issue in my MVC application (for making basic CRUD changes to a database) where the object parameter getting passed to my "Delete" post method has blank parameters, even though the object returned by the get method is correct. As a result, when I try to delete the object from the database I get the following exception:
A first chance exception of type 'System.ArgumentNullException' occurred in EntityFramework.dll
System.ArgumentNullException: Value cannot be null.
Parameter name: entity
at System.Data.Entity.ModelConfiguration.Utilities.RuntimeFailureMethods.Requires(Boolean condition, String userMessage, String conditionText)
at System.Data.Entity.DbSet`1.Remove(TEntity entity)
at MvcApplication1.HomeController.Delete(ISBN bookToDelete) in C:\Users\MMcCrimmon\Documents\Visual Studio 2012\Projects\MortonPublishingDatabaseInterface\MvcApplication1\Controllers\HomeController.vb:line 103
After a bit of digging I found this question: Missing something in "Delete" post method in MVC (EF 4.1), which seems to be identical, but the answers there did not resolve my problem. What am I doing wrong here?
Here's my controller code:
' GET: /Home/Delete/5
Function Delete(ByVal id As String) As ActionResult
Dim bookToDelete = _db.ISBNs.Find(id)
Return View(bookToDelete)
End Function
' POST: /Home/Delete/5
<HttpPost()> _
Function Delete(bookToDelete As ISBN) As ActionResult
Dim originalBook = _db.ISBNs.Find(bookToDelete.Product_Code)
Try
_db.ISBNs.Remove(originalBook)
_db.SaveChanges()
Return RedirectToAction("Index")
Catch exc As Exception
Return View(originalBook)
End Try
End Function
and here's the view for the Delete page:
#ModelType MvcApplication1.ISBN
#Code
ViewData("Title") = "Delete"
Layout = "~/Views/Shared/_Layout.vbhtml"
End Code
<h2>Delete</h2>
<h3>Are you sure you want to delete this?</h3>
<p/>
<fieldset>
<legend>ISBN</legend>
<div class="display-label">
<strong>#Html.DisplayNameFor(Function(model) model.Product_Code)</strong>
</div>
<div class="display-field">
#Html.DisplayFor(Function(model) model.Product_Code)
</div>
<div class="display-label">
<strong>#Html.DisplayNameFor(Function(model) model.Title)</strong>
</div>
<div class="display-field">
#Html.DisplayFor(Function(model) model.Title)
</div>
<div class="display-label">
<strong>#Html.DisplayNameFor(Function(model) model.ISBN_UPC)</strong>
</div>
<div class="display-field">
#Html.DisplayFor(Function(model) model.ISBN_UPC)
</div>
<div class="display-label">
<strong>#Html.DisplayNameFor(Function(model) model.ManualName)</strong>
</div>
<div class="display-field">
#Html.DisplayFor(Function(model) model.ManualName)
</div>
<div class="display-label">
<strong>#Html.DisplayNameFor(Function(model) model.PgCount)</strong>
</div>
<div class="display-field">
#Html.DisplayFor(Function(model) model.PgCount)
</div>
<div class="display-label">
<strong>#Html.DisplayNameFor(Function(model) model.BookSize)</strong>
</div>
<div class="display-field">
#Html.DisplayFor(Function(model) model.BookSize)
</div>
<div class="display-label">
<strong>#Html.DisplayNameFor(Function(model) model.ColorOrBW)</strong>
</div>
<div class="display-field">
#Html.DisplayFor(Function(model) model.ColorOrBW)
</div>
<div class="display-label">
<strong>#Html.DisplayNameFor(Function(model) model.PageCount)</strong>
</div>
<div class="display-field">
#Html.DisplayFor(Function(model) model.PageCount)
</div>
</fieldset>
#Using Html.BeginForm()
#Html.AntiForgeryToken()
#<p>
<input type="submit" value="Delete" /> |
#Html.ActionLink("Back to List", "Index")
</p>
End Using
Following the answer for Missing something in "Delete" post method in MVC (EF 4.1), here's the modified view (still doesn't work):
#ModelType MvcApplication1.ISBN
#Code
ViewData("Title") = "Delete"
Layout = "~/Views/Shared/_Layout.vbhtml"
End Code
<h2>Delete</h2>
<h3>Are you sure you want to delete this?</h3>
<p/>
#Using Html.BeginForm()
#Html.AntiForgeryToken()
#<fieldset>
<legend>ISBN</legend>
<div class="display-label">
<strong>#Html.DisplayNameFor(Function(model) model.Product_Code)</strong>
</div>
<div class="display-field">
#Html.DisplayFor(Function(model) model.Product_Code)
</div>
<div class="display-label">
<strong>#Html.DisplayNameFor(Function(model) model.Title)</strong>
</div>
<div class="display-field">
#Html.DisplayFor(Function(model) model.Title)
</div>
<div class="display-label">
<strong>#Html.DisplayNameFor(Function(model) model.ISBN_UPC)</strong>
</div>
<div class="display-field">
#Html.DisplayFor(Function(model) model.ISBN_UPC)
</div>
<div class="display-label">
<strong>#Html.DisplayNameFor(Function(model) model.ManualName)</strong>
</div>
<div class="display-field">
#Html.DisplayFor(Function(model) model.ManualName)
</div>
<div class="display-label">
<strong>#Html.DisplayNameFor(Function(model) model.PgCount)</strong>
</div>
<div class="display-field">
#Html.DisplayFor(Function(model) model.PgCount)
</div>
<div class="display-label">
<strong>#Html.DisplayNameFor(Function(model) model.BookSize)</strong>
</div>
<div class="display-field">
#Html.DisplayFor(Function(model) model.BookSize)
</div>
<div class="display-label">
<strong>#Html.DisplayNameFor(Function(model) model.ColorOrBW)</strong>
</div>
<div class="display-field">
#Html.DisplayFor(Function(model) model.ColorOrBW)
</div>
<div class="display-label">
<strong>#Html.DisplayNameFor(Function(model) model.PageCount)</strong>
</div>
<div class="display-field">
#Html.DisplayFor(Function(model) model.PageCount)
</div>
</fieldset>
#<p>
<input type="submit" value="Delete" /> |
#Html.ActionLink("Back to List", "Index")
</p>
End Using
Full disclosure: I'm new to MVC, ASP, and VB.NET, so please forgive me if I'm making some rookie mistake here...

Answer 1

You don't seem to be passing the "bookToDelete" parameter through to the DELETE method. In fact you shouldn't be passing this through as it's an object not a simple value. I would pass the "book id" through on delete post action (same as delete get action)
Altering the delete view form code by adding the following line between the #Using Html.BeginForm() and End Using lines
#Html.HiddenFor(model => model.id)
And change the DELETE post method in your controller to
Function Delete(id as string) As ActionResult
Dim originalBook = _db.ISBNs.Find(id)

Answer 2

You need to add a to your form indicating the parameter to pass to your controller.
E.g. If your controller is using "BookToDeleteID" as parameter name, your view html should look like this:
<form>
......
<input type="hidden" name="BookToDeleteID" value="A_NUMBER"/>
<input type="submit" value="delete"/>
</form>
Sometimes it has weird cases where you have to pass JSON objects to controllers. Maybe it's a data integrity concern by Microsoft. So I guess you have to parse the entire model for all actions.