将SelectedItem从下拉列表绑定到MVC 4中的模型对象

Question

I'm very new with MVC, so bear with me, but I can't seem to bind a value from a SelectList to an instance of the selected object during a postback in MVC 4.

Suppose I have to create a Teacher as a member of a School. I have a ViewModel class defined as such:

public class RegisterTeacherModel
{
    [Required]
    [Display(Name = "User name")]
    public string UserName { get; set; }

    [Required]
    [DataType(DataType.EmailAddress)]
    [Display(Name = "Email address")]
    public string Email { get; set; }

    [Required]
    [Display(Name = "School")]
    public School SelectedSchool { get; set; }

    [ScaffoldColumn(false)]
    public Guid UserId
    {
        get;
        set;
    }

    public SelectList PossibleSchools
    {
        get;
        private set;
    }

    public RegisterTeacherModel(IRepository<School> schoolRepo)
    {
        PossibleSchools = new SelectList(schoolRepo, "Id", "Name");
    }
}

And my View:

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

<fieldset>
    <legend>RegisterTeacherModel</legend>

    <div class="editor-label">
        @Html.LabelFor(model => model.UserName)
    </div>

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

    <div class="editor-label">
        @Html.LabelFor(model => model.SelectedSchool)
    </div>
    <div class="editor-field">
        @Html.DropDownListFor(model => model.SelectedSchool, Model.PossibleSchools)
    </div>
    <p>
        <input type="submit" value="Create" />
    </p>
</fieldset>
}

And finally, my Controller method:

    [HttpPost, ActionName("Create")]
    public ActionResult CreateTeacher(RegisterTeacherModel teacherModel)
    {
        if (ModelState.IsValid)
        {
            try
            {
              ...
            }
         }
    }

But when I receive the RegisterTeacherModel object back in my Create method in the Controller, SelectedSchool is always null. I must be missing something in the way the model binder re-creates the object references on postback. Can anyone point me in the right direction?

Answer 1

I think you touched on it with your second post: Try pointing the initial code to Model.SelectedSchool. <IdProperty>

<div class="editor-field">
  @Html.DropDownListFor(model => model.SelectedSchool.**<IdProperty>**, Model.PossibleSchools)
</div>

Answer 2

Well, I found a workaround. I still don't know if I'm missing something, but instead of using a School object in my ViewModel, I replaced it with the SelectedSchoolId as such:

public class RegisterTeacherModel
{
    [Required]
    [Display(Name = "User name")]
    public string UserName { get; set; }

    [Required]
    [DataType(DataType.EmailAddress)]
    [Display(Name = "Email address")]
    public string Email { get; set; }

    [Required]
    [Display(Name = "School")]
    public int SelectedSchoolId { get; set; }

    ...
}

And change my View dropdown to use this instead:

<div class="editor-field">
    @Html.DropDownListFor(model => model.SelectedSchoolId, Model.PossibleSchools)
</div>

And then in my controller, when creating the real model objects I can simply pull the School object from the School repository and associate it with the real Teacher object.