Unable to edit the user information in mvc - asp.net-mvc

Question

Here is my problem , So i wanted to only allowing the user to change/edit their password and username only.
My original model for customer is this
public string IC { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public string Username{ get; set; }
public string Password{ get; set; }
And this is my VM for the customer
public string Username{ get; set; }
public string Password{ get; set; }
And this is my controller for the edit function
public ActionResult Edit([Bind(Include = "Username,Password")] CustomersVM customersVM )
{
if (ModelState.IsValid)
{
db.Entry(customersVM ).State = EntityState.Modified;
db.SaveChanges();
return RedirectToAction("Index");
}
return View(customersVM );
}
view.cshtml
#Html.ValidationSummary(true, "", new { #class = "text-danger" })
#Html.HiddenFor(model => model.IC)
<div class="form-group">
#Html.LabelFor(model => model.Username, htmlAttributes: new { #class = "control-label col-md-2" })
<div class="col-md-10">
#Html.EditorFor(model => model.Username, new { htmlAttributes = new { #class = "form-control" } })
#Html.ValidationMessageFor(model => model.Username, "", new { #class = "text-danger" })
</div>
</div>
<div class="form-group">
#Html.LabelFor(model => model.Password, htmlAttributes: new { #class = "control-label col-md-2" })
<div class="col-md-10">
#Html.EditorFor(model => model.Password, new { htmlAttributes = new { #class = "form-control" } })
#Html.ValidationMessageFor(model => model.Password, "", new { #class = "text-danger" })
</div>
</div>
So this VM is to let the ModelState goes valid, which is will going right into the database but it turn out to turn this type of error
System.InvalidOperationException: 'The entity type CustomerVM is not part of the model for the current context.'

Answer 1

In order to edit/update a record, you need to identify that record first. I your case, your ViewModel is not what your database holds but the first model in your question. So you need to map that viewModel to the real model before saving or fetch the existing record then modify it then set it as modified before saving.
public ActionResult Edit([Bind(Include = "Username,Password")] CustomersVM customersVM )
{
if (ModelState.IsValid)
{
var existing = db.Customers.FirstOrDefault(x => x.Id == customersVM.Id);
if (existing != null)
{
existing.Username = customersVM.Username;
existing.Password = customerVM.Password;
db.Entry(existing ).State = EntityState.Modified;
db.SaveChanges();
return RedirectToAction("Index");
}
}
return View(customersVM );
}