Question

I have a teacher rating system. When I got to create a new comment about a teacher, I have a dropdownlistfor() list of classes that are available to the student can choose from. I want that dropdownlist to pass a Course Object in upon submitting but instead it’s just passing in null and giving me an error. I’m using a viewbag to display all the available courses.

Model:

    public class TeachersRatingsWall
{

    public int ID { get; set; }



    [Range(1, 5, ErrorMessage = "Invalid rating")]
    public Int32 StarRating { get; set; }

    [Required]
    public string PostComment { get; set; }

    public DateTime PostDate { get; set; }

    [Required]
    public string Teacher { get; set; } //?   or public Teacher Teacher { get; set; }

    public Guid PosterID { get; set; }

    public string PosterUserName { get; set; }

    //[Required] 
    public Course Course { get; set; }

    public Guid CourseID { get; set; }




    }
 }

Ropository:

     public IQueryable<TeachersRatingsWall> Select()
    {
        return table.Select(x => new TeachersRatingsWall
                                {
                                  ID = x.ID,
                                  StarRating = x.StarRating,
                                  PostComment = x.PostComment,
                                  PostDate = x.PostDate,
                                  Teacher = x.Teacher,
                                  PosterID = x.PosterID,
                                  CourseID = x.CourseID,
                                  Course = new Course {
                                      ID = x.CourseID,
                                      CourseNumber = x.CourseEntity.CourseNumber,
                                      Department = x.CourseEntity.Department,
                                      Description = x.CourseEntity.Description,
                                      Name = x.CourseEntity.Name

                                                        }

                                });

    }

Controller:

public ActionResult Create()

{

     ViewBag.allcourses = coursesservice.GetAllCoursesNamesAndNumbers().Select(x => x.Department + " " + x.CourseNumber);

        //-----------------------------------------------------------------------------------------------------------
        return View();
    } 


   [HttpPost]
    public ActionResult Create(TeachersRatingsWall collection)
    {           
        try
        {
            // TODO: Add insert logic here
            collection.PosterID = ((Guid)Membership.GetUser().ProviderUserKey);
            collection.PostDate = System.DateTime.Now;

            teacherratingservice.CreateComment(collection);
            return RedirectToAction("Index");
        }
        catch
        {
            return View();
        }
    }

View – Create.cshtml

        <div class="editor-label">
        @Html.Label("Course:")
    </div>
    <div class="editor-field">
        @Html.DropDownListFor(model => model.Course, new SelectList(ViewBag.allcourses))

    </div>

Answer 1

On your model you need the following

public int CourseId { get; set; }

and

public IList<SelectListItem> Courses { get; set; }  

On your Controller you have to populate these two model items together then in your view it should be something like this

@Html.DropDownListFor(model => model.CourseId, Model.Courses, "")

MVC will auto map that for you and select the necessary items for GET and POST