DropDownList允许用户选择“名称”，但在数据库中创建“ ID”

Question

I am trying to create a web application which will allow users to select a training course from DB, then 'apply' to this course. There application will be logged in "CourseRequests" table.

I have a table called "InternalCourses"
I have a tabled called "CourseRequests"

I have build a CREATE.CSHTML page which allows the user to select a course, and then hit 'create' it should create a record in the relevant table. My problem is because I need the user to select a CourseName, and have the program send back the relevant ID to the database, and discard the coursename. A screenshot of this page looks like so:

My Controller class:

    // GET: CourseRequests/Create
    public ActionResult Create()
    {
        ViewBag.InternalCourses = db.InternalCourses.ToList();
        ViewBag.EmployeeID = new SelectList(db.Employees, "EmployeeID", "FirstName");
        ViewBag.ManagerID = new SelectList(db.Employees, "ManagerID", "FirstName");
        ViewBag.CourseID = new SelectList(db.ExternalCourses, "CourseID", "CourseName");
        ViewBag.CourseID = new SelectList(db.InternalCourses, "CourseID", "CourseName");
        ViewBag.CourseID = new SelectList(db.TrainingFeedbacks, "CourseID", "Question");
        return View();
    }

My Create.cshtml

<!-- CourseID-->
        <div class="form-group">
            @Html.LabelFor(model => model.CourseID, "CourseID", htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.DropDownListFor(m => m.CourseID, new SelectList(ViewBag.InternalCourses, "CourseID", "CourseName"), new { @class = "form-control" } )
                @Html.ValidationMessageFor(model => model.CourseID, "", new { @class = "text-danger" })
            </div>

My (relevant) model diagram: The image shows a link from InternalCourse.CourseID , to CourseRequest.CourseID please note that the table CourseRequests, does not contain "CourseName" only ID.

Please could somebody advise me where I'm going wrong, I can see that I'm trying to put CourseName into ID field but don't get how I can change this.

Answer 1

Well, for starters you define ViewBag.CourseID three times, which is a total waste of resources as only the last time will stick. The first two are just wasted queries:

ViewBag.CourseID = new SelectList(db.ExternalCourses, "CourseID", "CourseName");
ViewBag.CourseID = new SelectList(db.InternalCourses, "CourseID", "CourseName");
ViewBag.CourseID = new SelectList(db.TrainingFeedbacks, "CourseID", "Question");

Next, when using ViewBag to store your select lists, you need to be careful not to clobber any of your model data. Anything in ModelState (which ViewBag is a part of) overrides anything on your model. Therefore, you'll never be able to show the selected value for the property CourseID when you have a select list stored in ViewBag.CourseID because the value will always be the select list itself, not what item was selected. Use a different name such as ViewBag.CourseChoices .

Finally, I'm not sure what problem you're actually having here. There is no difficulty in showing one thing as choices in a select list, like a name, while submitting something else, like an id. The constructor for SelectList should be called in the following format:

new SelectList(listOfItems, propertyToUseAsValue, propertyToUseAsText)

So, in your scenario, as long as you feed it "CourseID" and "CourseName", in that order, you'll get what you want. It's possible some of these other issues I mentioned are actually the source of your issues.