Using checkbox for multiple deletion in asp-mvc [duplicate]

This question already has an answer here:

• ASP.Net MVC checkbox values from view to custom controller method 2 answers

Let me first present the essential parts of my application:

This is my view:

Here is the code of my view:

    @using MvcApplication6.Models;
    @model List<Employee>

    @{
        ViewBag.Title = "Index";
    }

    <h2>Index</h2>

    <p>

        <a href="@Url.Action("Create")">Create Entry</a>

    </p>


    <p>@Html.ActionLink("Check departments", "Index", "Department")</p>

    <p><a href="@Url.Action("Summary")">Check summary</a></p>



@using (Html.BeginForm())
{
    @Html.AntiForgeryToken()
    @Html.ValidationSummary(true)

    <table border="1">

        <tr>
            <th>
                @Html.DisplayNameFor(model => model[0].id)
            </th>
            <th>
                @Html.LabelFor(model => model[0].firstname)
            </th>
            <th>
                @Html.LabelFor(model => model[0].lastname)
            </th>
            <th>
                @Html.DisplayNameFor(model => model[0].gender)
            </th>
            <th>
                @Html.DisplayNameFor(model => model[0].department)
            </th>
            <th>Action</th>
        </tr>




            @foreach (Employee mod in Model)
            {
                <tr>

                    <td>
                        <input type="hidden" value="@mod.id" name="id" id="id" />
                        @Html.DisplayFor(modelItem => mod.id)

                    </td>
                    <td>
                        @Html.DisplayFor(modelItem => mod.firstname)
                    </td>
                    <td>
                        @Html.DisplayFor(modelItem => mod.lastname)
                    </td>
                    <td>
                        @Html.DisplayFor(modelItem => mod.gender)
                    </td>
                    <td>
                        @Html.DisplayFor(modelItem => mod.department)
                    </td>
                    <td>
                        <button onclick="location.href='@Url.Action("Edit", new { id = mod.id })';return false;">Edit</button> |

                        @Html.CheckBoxFor(modelItem => mod.selected)


                    </td>

                </tr>

            }



        </table>
    <br />
    <input type="submit" value="submit" />
}

Here is my model:

 [Table("carl")]
public class Employee
{


    public int id { get; set; }

    [DisplayName("First Name")]
    [Required(ErrorMessage = "First name is required")]
    public string firstname { get; set; }


    [DisplayName("Last name")]
    [Required(ErrorMessage = "Last name is required")]
    public string lastname { get; set; }

    [DisplayName("Gender")]
    [Required(ErrorMessage = "Gender is required")]
    public string gender { get; set; }


    [DisplayName("Department")]
    [Range(1, 3)]
    [Required(ErrorMessage = "Dep name is required")]
    public int department { get; set; }

    [NotMapped]
    public bool selected { get; set; }
}

I am using Entity Framework and my context class is like this:

public class EmployeeContext: DbContext
{
    public DbSet<Employee> Employees { get; set; }
    public DbSet<Department> Departments { get; set; }
    public DbSet<gender> Genders { get; set; }

}

And lastly, here are is controller:

[HttpGet]
public ActionResult Index()
{

    EmployeeContext emp = new EmployeeContext();
    var adep = emp.Employees.ToList();

    return View(adep);
    }


 [HttpPost]
 public String Index(IEnumerable<Employee> emp)
  {

     if (emp.Count(x => x.selected) == 0)
     {
         return "0 selected";
     }
     else
     {
         return "Success";
     }
  }

Errors that i get is Additional information: Value cannot be null..

What i want to happen is that, all the selected checkboxes to be deleted once the user submits. I made two separate types of index for checking. There is not much functionality yet because i want to confirm it first if i am able to bind to the model. Is it because of the [NotMapped] Attribute? My database has id,firstname,gender,department and i don't want to add another column just for the sake of having some "flags".

The html helper for my checkbox is this line of code:

@Html.CheckBoxFor(modelItem => mod.selected)

And i attached them on every single table rows.