ASP.NET MVC Core Cascading DropDownList

Question

我无法找到教程/视频，该教程/视频展示了如何使用EntityFramework从数据库实现Cascading DropDownList。我使用ASP.NET MVC Core，EntityFramework Core和C＃。

截至目前，我能够将数据从我的数据库检索到我的3 DropDownList。

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，在用户选择城市后，它将显示与城市相关的邮政编码。

非常感谢任何帮助。

模型

    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; }
}

的ViewModels

    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; }
}

CustomerController

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例子中我有一个Root文件夹，根据我使用的下一个下拉列表中的哪个根文件夹会显示相应的子文件夹。

不确定是否有一个纯粹的asp.net解决方案但是，我使用了Jquery / Ajax。

您的代码应如下所示：

html list：

<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，您在.js文件中编写此代码，然后使用此语句<script src="~/js/example.js"></script>将其添加到特定视图中，不要忘记在任何其他javascript之前需要向项目添加jquery库，您的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（在return dbContext.CityTable.Where(c => c.StateId == id).ToList()方法中使用类似getCititesFromDatabaseByStateId(id)的内容），然后返回Json对象{ {1}}函数将创建一个选项列表并应用它：

success

在public IActionResult getCities(int id) { var cities = new List<City>(); cities = getCititesFromDatabaseByStateId(id); //call repository return Json(citites); } 考虑将ViewModel（IEnumerable<State/City/Zip>）更改为IEnumerable<T>。我也可以说你的模型很乱（但是如果你能从数据库中获取数据集中在使列表工作第一），那么考虑以后改进它们。

修复评论中提到的2个错误：

IEnumerable<SelectListItem>