asp.net-mvc - Entity Framework 中的多态性

Question

具体类(BankAccount 和 CreditCard)在 Controller 上不可见。

我被这个问题困住了。

我正在使用这个网站的例子:

http://weblogs.asp.net/manavi/archive/2010/12/28/inheritance-mapping-strategies-with-entity-framework-code-first-ctp5-part-2-table-per-type-tpt.aspx

观点

CreateUser:

如果选择了 CreditCard，它应该关联到 User 类。

图表

代码

用户 Controller :

    [HttpPost]
    public ActionResult Create(User user)//The Watch above came from this user instance
    {
        if (ModelState.IsValid)
        {

            context.User.Add(user);
            context.SaveChanges();
            return RedirectToAction("Index");  
        }

        ViewBag.PossibleBillingDetail = context.BillingDetail;
        return View(user);
    }

用户\_CreateOrEdit.cshtml:

User\Create.cshtml:

    @model TPTMVC.Models.User
    @using TPTMVC.Models;

<script src="http://ajax.microsoft.com/ajax/jQuery/jquery-1.5.js" type="text/javascript"></script> 
<script type="text/javascript">

    $(document).ready(function () {
        $('.divbank').hide();
        $('input[type=radio]').live('change', function () { updateweather(); });
    });

    function updateweather() {
        //alert();
        if ($('input[type=radio]:checked').val() == 'Bank') {
            $('.divcard').fadeOut(1000);
            $('.divcard').hide();
            $('.divbank').fadeIn(1000);
        }
        else {
            $('.divbank').fadeOut(1000);
            $('.divbank').hide();
            $('.divcard').fadeIn(1000);
            }

    }
        </script>
    <div id="json"></div>

@{
    ViewBag.Title = "Create";
}

<h2>Create</h2>

@using (Html.BeginForm())
{
@Html.ValidationSummary(true)
<fieldset>
    <legend>User</legend>

        @Html.Partial("_CreateOrEdit", Model)

        <div ='none' class="divcard">
            <div class="editor-label">
                @Html.LabelFor(model => ((CreditCard)model.billingDetail).ExpiryMonth)
            </div>
            <div class="editor-field">
                @Html.EditorFor(model => ((CreditCard)model.billingDetail).ExpiryMonth)
                @Html.ValidationMessageFor(model => ((CreditCard)model.billingDetail).ExpiryMonth)
            </div>

             <div class="editor-label">
                @Html.LabelFor(model => ((CreditCard)model.billingDetail).ExpiryYear)
            </div>
            <div class="editor-field">
                @Html.EditorFor(model => ((CreditCard)model.billingDetail).ExpiryYear)
                @Html.ValidationMessageFor(model => ((CreditCard)model.billingDetail).ExpiryYear)
            </div> 
        </div>

        <div='none' class="divbank">
            <div class="editor-label">
                @Html.LabelFor(model => ((BankAccount)model.billingDetail).BankName)
            </div>
            <div class="editor-field">
                @Html.EditorFor(model => ((BankAccount)model.billingDetail).BankName)
                @Html.ValidationMessageFor(model => ((BankAccount)model.billingDetail).BankName)
            </div>

             <div class="editor-label">
                @Html.LabelFor(model => ((BankAccount)model.billingDetail).Swift)
            </div>
            <div class="editor-field">
                @Html.EditorFor(model => ((BankAccount)model.billingDetail).Swift)
                @Html.ValidationMessageFor(model => ((BankAccount)model.billingDetail).Swift)
            </div> 
        </div>  
    <p>
        <input type="submit" value="Create" />
    </p>
</fieldset>
}

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

类代码:

namespace TPTMVC.Models{
public class BillingDetail
{
    [Key]
    [ForeignKey("user")]
    public int UserID { get; set; }
    public string Owner { get; set; }
    public string Number { get; set; }
    public virtual User user { get; set; }
}}

namespace TPTMVC.Models{
public class User
{
    public int UserId { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }

    public virtual BillingDetail billingDetail { get; set; }
}}
namespace TPTMVC.Models{
    [Table("BankAccounts")]
    public class BankAccount:BillingDetail
    {
        public string BankName { get; set; }
        public string Swift { get; set; }
    }}
namespace TPTMVC.Models{
[Table("CreditCards")]
public class CreditCard:BillingDetail
{
    public int CardType { get; set; }
    public string ExpiryMonth { get; set; }
    public string ExpiryYear { get; set; }
}}

问题

当我点击创建按钮时，我得到了这个结果:

我选择了一张 CreditCard，但结果是 BillingDetail。如您所见，我尝试进行转换，但出现错误。

:(

为什么只有 BillingDetail 出现在 UserController 上？

我的第一个解决方案

[HttpPost]
        public ActionResult Create(User user, CreditCard card, BankAccount bank, String Radio)
        {
            //String teste=formCollection["Radio"];
            if (ModelState.IsValid)
            {
                switch (Radio)
                {
                    case "CredCard":
                        user.billingDetail = card;
                        break;
                    case "Bank":
                        user.billingDetail = bank;
                        break;
                }
                context.User.Add(user);
                context.SaveChanges();
                return RedirectToAction("Index");  
            }

            ViewBag.PossibleBillingDetail = context.BillingDetail;
            return View(user);
        }

Answer 1

您正在将一个 User 对象传递给您的 View 。这有一个指向 BillingDetail 的导航属性，它可以是 CreditCard 或 BankAccount。您在 View (CreditCard)model 和 (BankAccount)model 中像这样转换它。它会在您创建时起作用，因为您正在转换一个 null 实例，但是当您有一个非 null 实例时它会导致运行时错误，因为其中一个转换会失败。

要解决此问题，您可以使用 model as CreditCard 和 model as BankAccount 然后在呈现适当的编辑器之前检查它们是否为空。但是您需要弄清楚当您的用户想要更改付款方式时该怎么做。

当表单返回到 Controller 时，因为您的 Create 方法签名采用了一个 User 参数，默认的 ModelBinder 知道它应该实例化一个 User。它完全有能力做到这一点，但无法确定如何处理 FormCollection 中出现的与 BillingDetail 相关的值。

通过继承，您不能依赖默认的 ModelBinder。您需要找出最适合您的方法。以下是我认为有用的一些引用资料:

Get an understanding of ModelBinding

Custom model binders - one person's opinion

The solution I went with - 但也要看看这里的所有其他解决方案!

下面是我项目中的一些示例代码，应该可以让您了解:

public ActionResult CreateOrEdit(FormCollection values)
{
    //The FormCollection is either a Property or a Block
    BaseProperty model;
    if (values["PropertyTypeID"] != null)
    {
        //it must be a Property!
        Property property = new Property();
        TryUpdateModel(property);
        _Uow.PropertyRepository.InsertOrUpdate(property);
        model = property;
    }
    else
    {
        Block block = new Block();
        TryUpdateModel(block);
        _Uow.BlockRepository.InsertOrUpdate(block);
        model = block;
    }
    //etc....