MVC 将脚手架字段更新为下拉列表

Question

Web Dev noob here. I am currently using VS2019 and have created a MVC App to provide CRUD functionality (SQL) to inhouse users. We have a CostCentre field which should be a dropdown and not a text input.

How do I change the code to display dropdown instead of text input?

This is what contained in my controller:

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Edit([Bind(Include = "Magic,EmployeeCode,UserName,Entity,AD_SAM,MSTelNum,CostCentre,SysUser_AD,Sys_User_K8")] EmpCosDim empCosDim)
{
    if (ModelState.IsValid)
    {
        db.Entry(empCosDim).State = EntityState.Modified;
        db.SaveChanges();
        return RedirectToAction("Index");
    }
    return View(empCosDim);
}

Am I looking at the right place?

UPDATE Edit View cshtml:

@model EmployeeBilling.EmpCosDim
@{
    ViewBag.Title = "Edit";
}

<h2>Edit</h2>

@using (Html.BeginForm())
{
    @Html.AntiForgeryToken()
    
    <div class="form-horizontal">
        <h4>EmpCosDim</h4>
        <hr />
        @Html.ValidationSummary(true, "", new { @class = "text-danger" })
        @Html.HiddenFor(model => model.Magic)

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

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

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

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

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

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

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

        <div class="form-group">
            @Html.LabelFor(model => model.Sys_User_K8, htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.EditorFor(model => model.Sys_User_K8, new { htmlAttributes = new { @class = "form-control" } })
                @Html.ValidationMessageFor(model => model.Sys_User_K8, "", new { @class = "text-danger" })
            </div>
        </div>

        <div class="form-group">
            <div class="col-md-offset-2 col-md-10">
                <input type="submit" value="Save" class="btn btn-default" />
            </div>
        </div>
    </div>
}

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

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

UPDATE Added the ForeignKey as per the link you sent, but still does not display the dropdown. I did the change here:

// EmpCosDim.cs :

namespace EmployeeBilling
{
    using System;
    using System.Collections.Generic;
    using System.ComponentModel.DataAnnotations;
    using System.ComponentModel.DataAnnotations.Schema;

    public class EmpCosDim
    {
        public int Magic { get; set; }
        public string EmployeeCode { get; set; }
        public string UserName { get; set; }
        public string Entity { get; set; }
        public string AD_SAM { get; set; }
        public string MSTelNum { get; set; }

        [ForeignKey("ContainingCostCentre")]
        public string CostCentre { get; set; }
        public virtual EmpCosDim ContainingCostCentre { get; set; }

        public string SysUser_AD { get; set; }
        public string Sys_User_K8 { get; set; }
    }
}

UPDATE So I've tried updating the CostCentre to a List in my EmpCosDim.cs file:

public class EmpCosDim
{
    [Key]
    public int Magic { get; set; }
    public string EmployeeCode { get; set; }
    public string UserName { get; set; }
    public string Entity { get; set; }
    public string AD_SAM { get; set; }
    public string MSTelNum { get; set; }

    public List<SelectCostCentreItem> CostCentre { get; set; }

    public string SysUser_AD { get; set; }
    public string Sys_User_K8 { get; set; }
}

public class SelectCostCentreItem
{
    public string CostCentre { get; set; }
}

But I'm getting an error on my Controller EmpCosDimsController.cs:

public ActionResult Index()
{
    return View(db.EmpCosDims.ToList());
}

This seems to be because I replaced:

public string CostCentre { get; set; }

with

public List<SelectCostCentreItem> CostCentre { get; set; }

How can I update my controller to see the List and display in a dropdown?

Answer 1

The drop down list of CostCentre in your edit screen will actually display the list of all CostCentre that you want to be selected. This list is not readily available in the EmpCosDim model and the view. You need to build a selectlist and pass to your view and make change in view to get that list and display as dropdown. Follow these steps -

In the Edit action (for Get not the post action) populate the view bag like this

ViewBag.CostCentre = new SelectList([db.Concetres], ["Name"], ["Name"], 
[empCosDim.CostCentre]);

Here you have to replace the bracketed items with your appropriate variable/method. For the select list constructor first one is the source/list of the all costcenters, second one the field name of the EmpCosDim that you want to save as the value when it get selected, third one the field of the EmpCosDim that you want to display in the dropdown, and last one is the value you want to be selected by default.

In the Edit view replace following code

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

with the next code block

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