尽管SelectList中计数为2，但下拉列表中未列出的名称

Question

I'm trying to figure out why everything compiles, the page loads, but there's nothing in the Managers drop down menu. The Engineers dropdown populates properly, but not the Managers . I thought that perhaps the query returned no results, but as it should, it returned 2 , I displayed the count and verified 2 matches in the table. Why would this not work?

   public ActionResult Create()
    {
        //var userId = User.Identity.GetUserId();
        //var user = 
        ViewBag.StatusId = new SelectList(db.statuses, "StatusId", "StatusName");
        ViewBag.SystemDetailId = new SelectList(db.systems, "SystemDetailId", "SystemName");


        var engineers = db.engineers;
        var managers = db.managers;
        var mte = db.ManagersToEngineers;
        List<Manager> matchedManager = null;
        Engineer matchedEngineer = null;

        if (this.User.Identity.IsAuthenticated)
        {
            var userEmail = this.User.Identity.Name;
            matchedEngineer = engineers.Where(x => x.email == userEmail).FirstOrDefault();
            if (matchedEngineer != null)
            {
                matchedManager = mte.Where(x => x.EngineerId == matchedEngineer.PersonId).Select(x => x.manager).ToList();
            }

        }

        if (matchedEngineer != null)
        {
            ViewBag.EngineerId = new SelectList(new List<Engineer> { matchedEngineer }, "PersonId", "FullName");
            ViewBag.ManagerId = new SelectList(matchedManager, "PersonId", "FullName");
        }
        else
        {
            ViewBag.EngineerId = new SelectList(engineers, "PersonId", "FullName");
            ViewBag.ManagerId = new SelectList(managers, "PersonId", "FullName");
        } 

        return View();
    }

Here's the cshtml for create (UPDATE: Engineer drop down shared for reference):

    <div class="form-group">
        @Html.LabelFor(model => model.EngineerId, htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.DropDownList("EngineerId", null, htmlAttributes: new { @class = "form-control" })
            @Html.ValidationMessageFor(model => model.engineer.FullName, "", new { @class = "text-danger" })
        </div>
    </div>

    <div class="form-group">
        @Html.LabelFor(model => model.ManagerId, htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.DropDownList("ManagerId", null, htmlAttributes: new { @class = "form-control" })
            @Html.ValidationMessageFor(model => model.manager.FullName, "", new { @class = "text-danger" })
        </div>
    </div>

Answer 1

Did you mean to instantiate a new List of Manager in the first line of ViewBag.ManagerId ?

if (matchedEngineer != null)
    {
        ViewBag.EngineerId = new SelectList(new List<Engineer> { matchedEngineer }, "PersonId", "FullName");
        // new up list below
        ViewBag.ManagerId = new SelectList(new List<Manager>, "PersonId", "FullName");
    }

Answer 2

Turns out I was missing the proper ForeignKey annotations in the change model it was being displayed from.

public class ManagerToEngineer
{
    [Key]
    public int ManagerToEngineerId { get; set; }

    [ForeignKey("engineer")]
    public int EngineerId { get; set; }

    [ForeignKey("manager")]
    public int ManagerId { get; set; }

    public virtual Engineer engineer { get; set; }
    public virtual Manager manager { get; set; }

}