ASP MVC Model Binding of DropDown fail

Question

I have ASP MVC 4 project. I have problem that when I try to create new Survey the code in the controller also fail to bind the posted form data to the model.

The specific error is:

The parameter conversion from type 'System.String' to type 'DNASurvey.Models.Tenant' failed because no type converter can convert between these types. {System.InvalidOperationException}

Those are the models I have:

public class Tenant {
    [Key]
    public string TenantID { get; set; }
    public string Name { get; set; }

    public virtual ICollection<Survey> Surveys { get; set; }
  }

  public class Survey {
    [Key]
    public string SurveyID { get; set; }

    [Required]
    public virtual Tenant Tenant { get; set; }

    [Required]
    [StringLength(100, MinimumLength=5)]
    public string Title { get; set; }

    [Required]
    public DateTime CreatedAt { get; set; }

    [Required]
    public uint CurrentRoundIndex { get; set; }
  }

I also have SurveyController with this relavant code:

public ActionResult Create() {
  AddPossibleTenants();
  return View();
}

//
// POST: /Survey/Create

[HttpPost]
public ActionResult Create(Survey survey) {
  if (ModelState.IsValid) {
    survey.SurveyID = EncodeNameToSingleString(survey.Title);
    db.Surveys.Add(survey);
    db.SaveChanges();
    return RedirectToAction("Index");
  }

  AddPossibleTenants();
  return View(survey);
}

private void AddPossibleTenants() {
  ViewBag.PossibleTenants = db.Tenants.ToList();
}

And this view for create:

@model DNASurvey.Models.Survey

@{
    ViewBag.Title = "Create";
}

<h2>Create</h2>

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

    <fieldset>
        <legend>Survey</legend>

        <div class="editor-label">
            @Html.LabelFor(model => model.Tenant)
        </div>
        <div class="editor-field">
            @Html.DropDownListFor(model => model.Tenant, new SelectList(ViewBag.PossibleTenants, "TenantID", "Name"))
            @Html.ValidationMessageFor(model => model.Tenant)
        </div>

        <div class="editor-label">
            @Html.LabelFor(model => model.Title)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.Title)
            @Html.ValidationMessageFor(model => model.Title)
        </div>

        <div class="editor-label">
            @Html.LabelFor(model => model.CreatedAt)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.CreatedAt)
            @Html.ValidationMessageFor(model => model.CreatedAt)
        </div>

        <p>
            <input type="submit" value="Create" />
        </p>
    </fieldset>
}

<div>
    @Html.ActionLink("Back to List", "Index")
</div>

@section Scripts {
    @Scripts.Render("~/bundles/jqueryval")
}

score 0 · Answer 1 · edited May 23 '17 at 12:21

0

Your form is generating a select element for Tenant, which will pass back a simple name-value pair. This won't bind to the Tenant property of your model, because Tenant is defined in your model as an object, not a string. You'll need to define your own custom model-binder to get this to work.

edited May 23 '17 at 12:21

Community

1
1

answered Aug 05 '12 at 13:12

Faust

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score 0 · Answer 2 · answered Aug 05 '12 at 13:39

0

I've found this series of posts about EF and MVC. This post explain how to use the scaffold command to create controllers and how to build the model so both EF and MVC will work right.

answered Aug 05 '12 at 13:39

Ido Ran

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ASP MVC Model Binding of DropDown fail

2 Answers2