Post List of lists of RadioButtons MVC

Question

I have an Attendance program in which I want to assign Students to AttendanceTakers. I am using a table where the headers are the AttendanceTakers and the rows are Students and each cell has a RadioButton. It is basically a double array of RadioButtons. My problem is I can't get it to post.

My AttendanceTaker class

public class SessionAttendanceTaker
    {

        public int Id { get; set; }

        [ForeignKey("Session")]
        public int SessionId { get; set; }
        public Session Session { get; set; }

        [Display(Name="Attendance Taker")]
        [ForeignKey("User")]
        public string AttendanceTakerId { get; set; }
        [Display(Name = "Attendance Taker")]
        public User User { get; set; }

        public List<Student> Students { get; set; }
    }

And the Student that is in the course class

public class StudentSession 
    {

        public int Id { get; set; }

        [ForeignKey("Session")]
        [DisplayName("Session")]
        public int SessionId { get; set; }
        public Session Session { get; set; }

        [ForeignKey("Student")]
        [DisplayName("Student")]
        public int StudentId { get; set; }
        public Student Student { get; set; }

        [DisplayName("Credits Awarded")]
        public int Credit { get; set; }
}

Student class

public class Student 
    {
        public int Id { get; set; }


        [ForeignKey("User")]
        public string UserId { get; set; }

        [DisplayName("Name")]
        public virtual User user { get; set; }

        public Student() 
        {

        }
  }

The View

@using (Html.BeginForm())
{

    <div class="form-horizontal">
        <table>
            <thead>
                <tr>
                    <th> Name &nbsp; &nbsp;</th>

                    @{
                        foreach (var attendanceTaker in Model.SessionAttendanceTakers)
                        {
                            <th>@attendanceTaker.User.LastName, @attendanceTaker.User.FirstName &nbsp; &nbsp;</th>
                        }
                    }

                </tr>
            </thead>
            <tbody>

                @{
                    //See https://stackoverflow.com/questions/7667495/mvc-radiobuttons-in-foreach to try and clean the foreach
                    foreach (var studentSession in Model.StudentSessions)
                    {

                        <tr>
                            <td>
                                @studentSession.Student.User.LastName, @studentSession.Student.User.FirstName
                            </td>
                            @foreach (var attendanceTaker in Model.SessionAttendanceTakers)
                            {
                                @Html.EditorFor(Model => Model.SessionAttendanceTakers, "StudentsToAttendanceTakersModel", "" + studentSession.StudentId, new { htmlAttributes = new { @class = "form-control" } })
                            }

                        </tr>
                    }
                }
            </tbody>
        </table>

        <div class="form-group">
            <div class="col-md-offset-2 col-md-10">
                <input type="submit" value="Assign" class="btn btn-default" />
            </div>
        </div>
    </div>
}

and EditorTemplate

@model IEnumerable<SessionAttendanceTaker>
@using Attendance.Models


<td>
    @Html.RadioButtonFor(model => model, new { htmlAttributes = new { @class = "form-control" } })
</td>

As an aside I would love to get rid of the foreaches as per this post but since I don't know how many attendance takers or students there will be until runtime I can't figure out how to do that besides for just moving them to the Editor and I don't see a point to that.

Also the Controller

[HttpPost]
        public ActionResult Assign(StudentsToAttendanceTakersModel model)
        {

            return RedirectToAction("Index");
        }

I have a breakpoint on the return and the attendanceTakers is null and Student sessions has a count of 0.

Additionally, using FormCollection

public ActionResult Assign(FormCollection o)

only gives me the Students who's RadioButton was clicked but not the AttendanceTaker. If more info is needed let me know. Thanks.

EDIT Model

public class StudentsToAttendanceTakersModel
    {
        public IEnumerable<StudentSession> StudentSessions { get; set; }
        public IEnumerable<SessionAttendanceTaker> SessionAttendanceTakers { get; set; }

        public StudentsToAttendanceTakersModel() { }
    }

Answer 1

You're creating radio buttons which do not relate to your model, and you're trying to bind them to a complex object (SessionAttendanceTaker) - a radio button posts back a simple value (and you are not even giving the radio buttons a valid value - the 2nd parameter of RadioButtonFor() is the value).

You are editing data, so you should start by creating view models which represent what you want to display in the view.

public class StudentVM
{
    public int ID { get; set; }
    public string Name { get; set; }
    [Required(ErrorMessage = "Please select an attendance taker")]
    public int? SelectedAttendanceTaker { get; set; }
}
public class AttendanceTakerVM
{
    public int ID { get; set; }
    public string Name { get; set; }
}
public class StudentAttendanceTakersVM
{
    public List<StudentVM> Students { get; set }
    public IEnumerable<AttendanceTakerVM> AttendanceTakers { get; set; }
}

So that your view will be

@model StudentAttendanceTakersVM
....
@using (Html.BeginForm())
{
    <table>
        <thead>
            <tr>
                <th>Student</th>
                @foreach(var taker in Model.AttendanceTakers)
                {
                    <th>@taker.Name</th>
                }
                <th></th>
            </tr>
        </thead>
        <tbody>
        @for(int i = 0; i < Model.Students.Count; i++)
        {
            <tr>
                <td>
                    @Model.Students[i].Name
                    @Html.HiddenFor(m => m.Students[i].ID)
                    @Html.HiddenFor(m => m.Students[i].Name)
                </td>
                @foreach(var taker in Model.AttendanceTakers)
                {
                    <td>@Html.RadioButtonFor(m => m.Students[i].SelectedAttendanceTaker, taker.ID, new { @class = "form-control" })</td>
                }
                <td>@Html.ValidationMessageFor(m => m.Students[i].SelectedAttendanceTaker)</td>
            </tr>
        }
        </tbody>
    </table>
    <input type="submit" ... />
}

Your GET method will then initialize an instance of you view model and pass it to the view, for example, for a 'Create' method

public ActionResult Create()
{
    var students = db.Students.Select(x => new StudentVM
    {
        ID = x.Id,
        Name = x.User.FirstName + " " + x.User.LastName // adjust as required
    }).ToList();
    var attendanceTakers = db.SessionAttendanceTakers.Select(x => new AttendanceTakerVM
    {
        ID = x.Id,
        Name = x.User.FirstName + " " + x.User.LastName // adjust as required    
    });
    StudentAttendanceTakersVM model = new StudentAttendanceTakersVM
    {
        Students = students,
        AttendanceTakers = attendanceTakers
    };
    return View(model);
}

And the POST method will be

public ActionResult Create(StudentAttendanceTakersVM model)
{
    if (!ModelState.IsValid)
    {
        return View(model);
    }
    // loop through model.Students to get the ID of the Student and its selected AttendanceTaker
    // initialize the data models and save to the database
    return RedirectToAction("Index");
}