ASP.NET MVC 核心级联 DropDownList

Question

我无法找到展示如何使用 EntityFramework 从数据库实现级联 DropDownList 的教程/视频。我正在使用 ASP.NET MVC Core、EntityFramework Core 和 C#。

到目前为止，我可以将数据库中的数据检索到我的 3 DropDownList 中。

我希望能够完成的是让用户首先选择一个州，然后显示与该州相关的所有城市。然后在用户选择一个城市后，它将显示与该城市相关的邮政编码。

任何帮助将不胜感激。

楷模

    public class Customer
{
    public int CustomerId { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }

    public int StateId { get; set; }
    public int CityId { get; set; }
    public int ZipId { get; set; }

    public State State { get; set; }
    public City City { get; set; }
    public Zip Zip { get; set; }
}

    public class State
{
    public int StateId { get; set; }
    public string Abbr { get; set; }

    public List<Customer> Customers { get; set; }
}

    public class City
{
    public int CityId { get; set; }
    public string Name { get; set; }

    public int StateId { get; set; }
    public State State { get; set; }

    public List<Customer> Customers { get; set; }
}

    public class Zip
{
    public int ZipId { get; set; }
    public string PostalCode { get; set; }

    public int CityId { get; set; }
    public City City { get; set; }

    public List<Customer> Customers { get; set; }
}

视图模型

    public class CustomerFormVM
{
    public int CustomerId { get; set; }

    [Display(Name = "First Name")]
    [StringLength(50)]
    public string FirstName { get; set; }

    [Display(Name = "Last Name")]
    [StringLength(50)]
    public string LastName { get; set; }

    [Required(ErrorMessage = "Select State")]
    [Display(Name = "State")]
    public int StateId { get; set; }

    //public IEnumerable<State> States { get; set; }
    public IEnumerable<SelectListItem> States { get; set; }

    [Required(ErrorMessage = "Select City")]
    [Display(Name = "City")]
    public int CityId { get; set; }

    //public IEnumerable<City> Citys { get; set; }
    public IEnumerable<SelectListItem> Citys { get; set; }

    [Required(ErrorMessage = "Select Zip")]
    [Display(Name = "Zip")]
    public int ZipId { get; set; }

    //public IEnumerable<Zip> Zips { get; set; }
    public IEnumerable<SelectListItem> Zips { get; set; }
}

客户控制器

public class CustomerController : Controller
{
    private MultiDbContext db;

    public CustomerController(MultiDbContext context)
    {
        db = context;
    }

    // GET: /<controller>/
    public IActionResult Index()
    {
        return View(db.Customers.ToList());
    }

    public IActionResult getCititesFromDatabaseByStateId(int id)
    {
        return View(db.Citys.Where(c => c.StateId == id).ToList());
    }

    public IActionResult getCities(int id)
    {
        var cities = new List<City>();
        cities = getCititesFromDatabaseByStateId(id); //call repository
        return Json(cities);
    }

    public ActionResult Create()
    {
        var states = db.States.ToList();
        var citys = db.Citys.ToList();
        var zips = db.Zips.ToList();

        var viewModel = new CustomerFormVM
        {
            States = states,
            Citys = citys,
            Zips = zips
        };

        return View(viewModel);
    }


    [HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult Create(CustomerFormVM vm)
    {
        if (ModelState.IsValid)
        {
            var customer = new Customer();
            {
                customer.FirstName = vm.FirstName;
                customer.LastName = vm.LastName;
                customer.StateId = vm.StateId;
                customer.CityId = vm.CityId;
                customer.ZipId = vm.ZipId;
            }
            db.Customers.Add(customer);
            db.SaveChanges();
            return RedirectToAction("Index");
        }

        else
        {
            vm.States = db.States.ToList();
            vm.Citys = db.Citys.ToList();
            vm.Zips = db.Zips.ToList();
            return View(vm);
        }
    }


    public ActionResult Edit(int? id)
    {
        if (id == null)
        {
            return NotFound();
        }

        var customervm = new CustomerFormVM();
        {
            Customer customer = db.Customers.SingleOrDefault(c => c.CustomerId == id);

            if (customer == null)
            {
                return NotFound();
            }

            customervm.CustomerId = customer.CustomerId;
            customervm.FirstName = customer.FirstName;
            customervm.LastName = customer.LastName;

            // Retrieve list of States
            var states = db.States.ToList();
            customervm.States = states;

            // Retrieve list of Citys
            var citys = db.Citys.ToList();
            customervm.Citys = citys;

            // Retrieve list of Citys
            var zips = db.Zips.ToList();
            customervm.Zips = zips;

            // Set the selected state
            customervm.StateId = customer.StateId;

            // Set the selected city
            customervm.CityId = customer.CityId;

            // Set the selected zip
            customervm.ZipId = customer.ZipId;
        }
        return View(customervm);
    }


    [HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult Edit(CustomerFormVM vmEdit)
    {
        if (ModelState.IsValid)
        {
            Customer customer = db.Customers.SingleOrDefault(c => c.CustomerId == vmEdit.CustomerId);

            if (customer == null)
            {
                return NotFound();
            }

            customer.FirstName = vmEdit.FirstName;
            customer.LastName = vmEdit.LastName;
            customer.StateId = vmEdit.StateId;
            customer.CityId = vmEdit.CityId;
            customer.ZipId = vmEdit.ZipId;

            db.Entry(customer).State = EntityState.Modified;
            db.SaveChanges();
            return RedirectToAction("Index");
        }
        return View(vmEdit);
    }
}

创建视图

        <div class="form-group">
        @Html.LabelFor(c => c.FirstName)
        @Html.TextBoxFor(c => c.FirstName, new { @class = "form-control" })
    </div>

    <div class="form-group">
        @Html.LabelFor(c => c.LastName)
        @Html.TextBoxFor(c => c.LastName, new { @class = "form-control" })
    </div>

    <div class="form-group">
        @*@Html.LabelFor(s => s.StateId)
            @Html.DropDownListFor(s => s.StateId, new SelectList(Model.States, "StateId", "Abbr"), "", new { @class = "form-control" })
            @Html.ValidationMessageFor(s => s.StateId)*@

        <label asp-for="StateId "></label>
        <select asp-for="StateId " asp-items="Model.States" class="form-control" id="state-target"></select>
        <span asp-validation-for="StateId " class="text-danger"></span>
    </div>

    <div class="form-group">
        @*@Html.LabelFor(ct => ct.CityId)
            @Html.DropDownListFor(ct => ct.CityId, new SelectList(Model.Citys, "CityId", "Name"), "", new { @class = "form-control" })
            @Html.ValidationMessageFor(ct => ct.CityId)*@

        <label asp-for="CityId"></label>
        <select asp-for="CityId" asp-items="Model.Citys" class="form-control" id="city-target"></select>
        <span asp-validation-for="CityId" class="text-danger"></span>
    </div>

    <div class="form-group">
        @Html.LabelFor(z => z.ZipId)
        @Html.DropDownListFor(z => z.ZipId, new SelectList(Model.Zips, "ZipId", "PostalCode"), "", new { @class = "form-control" })
        @Html.ValidationMessageFor(z => z.ZipId)
    </div>

    <div class="form-group">
        <button type="submit" class="btn btn-primary">Submit</button>
    </div>
}

@section scripts {
    <script src="~/lib/jquery-validation/dist/jquery.validate.js"></script>
    <script src="~/lib/jquery-validation-unobtrusive/jquery.validate.unobtrusive.js"></script>
    <script src="~/lib/js/example.js"></script>,
}

Answer 1

我有类似的情况，但在我的示例中，我有一个根文件夹，根据我使用的根文件夹，下一个下拉列表将显示相应的子文件夹。

不确定是否有纯粹的 asp.net 解决方案，但是，我为此使用了 Jquery/Ajax。

您的代码应如下所示：

html列表：

<label asp-for="StateId "></label>
<select asp-for="StateId " asp-items="Model.States" class="form-control" id="state-target"></select>
<span asp-validation-for="StateId " class="text-danger"></span>

<label asp-for="CityId"></label>
<select asp-for="CityId" asp-items="Model.Citys" class="form-control" id="city-target"></select>
<span asp-validation-for="CityId" class="text-danger"></span>

Jquery 代码，你把它写在 .js 文件中，然后用这个语句把它添加到一个特定的视图中<script src="~/js/example.js"></script>，不要忘记你需要在任何其他 javascript 之前向你的项目添加一个 jquery 库，你example.js将包含：

$(document).ready(function () {
  $("#state-target").on("change", function () {
    $list = $("#city-target");
    $.ajax({
        url: "/getCities",
        type: "GET",
        data: { id: $("#state-target").val() }, //id of the state which is used to extract cities
        traditional: true,
        success: function (result) {
            $list.empty();
            $.each(result, function (i, item) {
                $list.append('<option value="' + item["CityId"] + '"> ' + item["Name"] + ' </option>');
            });
        },
        error: function () {
            alert("Something went wrong call the police");
        }
    });
  });
});

Ajax 请求将在 Controller 中调用此操作，该操作将从数据库中检索城市列表（使用类似方法return dbContext.CityTable.Where(c => c.StateId == id).ToList()内部的内容getCititesFromDatabaseByStateId(id)），然后返回 Json 对象，该success函数将创建一个选项列表并应用它：

public IActionResult getCities(int id)
{
    var cities = new List<City>();
    cities = getCititesFromDatabaseByStateId(id); //call repository
    return Json(citites);
}

在您ViewModel考虑将IEnumerable<State/City/Zip>( IEnumerable<T>)更改为IEnumerable<SelectListItem>. 我也可以说你的模型很乱（但如果你可以从数据库中获取数据专注于让列表第一次工作），请考虑稍后改进它们。

修复评论中提到的 2 个错误：

public List<City> getCititesFromDatabaseByStateId(int id)
{
    return db.Citys.Where(c => c.StateId == id).ToList();
}

public ActionResult Create()
{
     var states = new SelectList(db.States.ToList(), "StateId", "Abbr");
     var citys = new SelectList(db.Citys.ToList(), "CityId", "Name");
     var zips = new SelectList(db.Zips.ToList(), "ZipId", "Code");

     var viewModel = new CustomerFormVM
     {
         States = states,
         Citys = citys,
         Zips = zips
     };

     return View(viewModel);
}