MVC filter on dropdownlist using entity framework scaffolding and Razor

Question

This is a really elementary question and I have searched for an answer but there seems to be none to be found. This is dealing with the Scaffolded MVC5 edit.cshtml using VS2015.

I have a 1:M relationship between 2 tables, and the child table has a @Html.DropDownList as a foreign key to the parent. I need to filter that @Html.DropDownList. These are the specifics:

One AssociationList has many AgsweepParameters.

The primary key of AssociationList is AssociationListId Therefore the AssociationListId field is the Foreign key in the AgsweepParameter table.

Using EntityFramework, and MVC5 Scaffolding, I created the crud views/controllers using Entity Framework as the model.

The generated declaration for that dropdown looks like this:

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

Question: How do I filter that dropdown list so that AssociationList.AssociationType=="ACA"?

Note that I use a similar filter on the Index.cshtml on AssociationList table which looks like this:

            @foreach (var item in Model.Where(row=>row.AssociationType=="ACA")) {
                <tr>
                    <td>
                        @Html.DisplayFor(modelItem => item.Name)
                    </td>
                    <td>
                        @Html.ActionLink("Edit", "Edit", new { id=item.AssociationListId }) |
                        @Html.ActionLink("Delete", "Delete", new { id=item.AssociationListId })
                    </td>
                </tr>
            }

Answer 1

Fundamental MVC here. I had to do the following:

Understand that the controller is the object that defines the filter and not the view. Therefore I go to the controller for public ActionResult Edit(int? id) and change

            ViewBag.AssociationListId = new SelectList(filteredAssociations, "AssociationListId", "Name", agsweepParameter.AssociationListId);

to

            IEnumerable<AssociationList> filteredAssociations = db.AssociationLists.Where(row => row.AssociationType == "ACA");
            ViewBag.AssociationListId = new SelectList(filteredAssociations, "AssociationListId", "Name", agsweepParameter.AssociationListId);