MVC 3 模型绑定子类型(抽象类或接口) [英] MVC 3 Model Binding a Sub Type (Abstract Class or Interface)

问题描述

假设我有一个 Product 模型，Product 模型有一个 ProductSubType(抽象)属性，我们有两个具体的实现 Shirt 和 Pants.

这是来源:

 公共类产品{公共 int Id { 获取；放;}[必需的]公共字符串名称 { 获取；放;}[必需的]公共小数点?价格{得到;放;}[必需的]公众号?产品类型{获取；放;}公共 ProductTypeBase 子产品 { 获取；放;}}公共抽象类 ProductTypeBase { }公共类衬衫:ProductTypeBase{[必需的]公共字符串颜色 { 获取；放;}public bool HasSleeves { get;放;}}公共类裤子:ProductTypeBase{[必需的]公共字符串颜色 { 获取；放;}[必需的]公共字符串大小 { 获取；放;}}

在我的 UI 中，用户有一个下拉菜单，他们可以选择产品类型，然后根据正确的产品类型显示输入元素.我已经弄清楚了所有这些(使用 ajax get 进行下拉更改，返回部分/编辑器模板并相应地重新设置 jquery 验证).

接下来，我为 ProductTypeBase 创建了一个自定义模型绑定器.

 公共覆盖对象 BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext){ProductTypeBase subType = null;var productType = (int)bindingContext.ValueProvider.GetValue("ProductType").ConvertTo(typeof(int));如果(产品类型 == 1){var 衬衫 = 新衬衫();shirt.Color = (string)bindingContext.ValueProvider.GetValue("SubProduct.Color").ConvertTo(typeof(string));shirt.HasSleeves = (bool)bindingContext.ValueProvider.GetValue("SubProduct.HasSleeves").ConvertTo(typeof(bool));子类型 = 衬衫；}否则如果(产品类型 == 2){var 裤子 = 新裤子();pants.Size = (string)bindingContext.ValueProvider.GetValue("SubProduct.Size").ConvertTo(typeof(string));pants.Color = (string)bindingContext.ValueProvider.GetValue("SubProduct.Color").ConvertTo(typeof(string));子类型 = 裤子；}返回子类型；}}

这将正确绑定值并且在大多数情况下都有效，除非我丢失了服务器端验证.所以我预感我做错了，我做了更多的搜索，发现了 Darin Dimitrov 的这个答案:

ASP.NET MVC 2 - 绑定到抽象模型

所以我将模型绑定器切换为仅覆盖 CreateModel，但现在它不绑定值.

protected override object CreateModel(ControllerContext controllerContext, ModelBindingContext bindingContext, Type modelType){ProductTypeBase subType = null;var productType = (int)bindingContext.ValueProvider.GetValue("ProductType").ConvertTo(typeof(int));如果(产品类型 == 1){subType = 新衬衫()；}否则如果(产品类型 == 2){subType = 新裤子()；}返回子类型；}

通过 MVC 3 src，似乎在 BindProperties 中，GetFilteredModelProperties 返回一个空结果，我认为是因为 bindingcontext 模型设置为没有任何属性的 ProductTypeBase.

谁能发现我做错了什么?这似乎不应该这么困难.我确定我遗漏了一些简单的东西......我有另一种选择，而不是在 Product 模型中拥有一个 SubProduct 属性，而只是为衬衫和裤子拥有单独的属性.这些只是视图/表单模型，所以我认为这是可行的，但如果有任何了解正在发生的事情，我希望让当前的方法起作用......

感谢您的帮助！

更新:

我没说清楚，但是我添加的自定义模型绑定器，继承自 DefaultModelBinder

答案

设置 ModelMetadata 和 Model 是缺失的部分.谢谢玛纳斯！

protected override object CreateModel(ControllerContext controllerContext, ModelBindingContext bindingContext, Type modelType){如果(modelType.Equals(typeof(ProductTypeBase))){类型实例化类型 = null;var productType = (int)bindingContext.ValueProvider.GetValue("ProductType").ConvertTo(typeof(int));如果(产品类型 == 1){实例化类型 = 类型(衬衫)；}否则如果(产品类型 == 2){实例化类型 = 类型(裤子)；}var obj = Activator.CreateInstance(instantiationType);bindingContext.ModelMetadata = ModelMetadataProviders.Current.GetMetadataForType(null, instantiationType);bindingContext.ModelMetadata.Model = obj;返回对象；}返回 base.CreateModel(controllerContext, bindingContext, modelType);}

解决方案

这可以通过重写 CreateModel(...) 来实现.我会用一个例子来证明这一点.

1.让我们创建一个模型和一些基类和子类.

公共类 MyModel{公共 MyBaseClass BaseClass { 获取；放;}}公共抽象类 MyBaseClass{公共虚拟字符串 MyName{得到{返回MyBaseClass"；}}}公共类 MyDerievedClass : MyBaseClass{公共 int MyProperty { 获取；放;}公共覆盖字符串 MyName{得到{返回MyDerievedClass"；}}}

2.现在创建一个模型绑定器并覆盖 CreateModel

公共类 MyModelBinder : DefaultModelBinder{受保护的覆盖对象 CreateModel(ControllerContext controllerContext, ModelBindingContext bindingContext, Type modelType){///MyBaseClass 和 MyDerievedClass 是硬编码的.///我们可以使用反射来读取程序集并获取任何基类型的具体类型if (modelType.Equals(typeof(MyBaseClass))){类型实例化类型 = typeof(MyDerievedClass);var obj=Activator.CreateInstance(instantiationType);bindingContext.ModelMetadata = ModelMetadataProviders.Current.GetMetadataForType(null, instantiationType);bindingContext.ModelMetadata.Model = obj;返回对象；}返回 base.CreateModel(controllerContext, bindingContext, modelType);}}

3.现在在控制器中创建获取和发布操作.

[HttpGet]公共 ActionResult 索引(){ViewBag.Message = "欢迎使用 ASP.NET MVC！";MyModel 模型 = new MyModel();model.BaseClass = new MyDerievedClass();返回视图(模型)；}[HttpPost]公共 ActionResult 索引(MyModel 模型){返回视图(模型)；}

4.现在在 global.asax 中将 MyModelBinder 设置为默认 ModelBinder 这样做是为了为所有动作设置默认模型绑定器，对于单个动作，我们可以在动作参数中使用 ModelBinder 属性)

protected void Application_Start(){AreaRegistration.RegisterAllAreas();ModelBinders.Binders.DefaultBinder = new MyModelBinder();RegisterGlobalFilters(GlobalFilters.Filters);RegisterRoutes(RouteTable.Routes);}

5.现在我们可以创建 MyModel 类型的视图和 MyDerievedClass 类型的部分视图

Index.cshtml

@model MvcApplication2.Models.MyModel@{ViewBag.Title = "索引";布局 = "~/Views/Shared/_Layout.cshtml";}<h2>索引</h2>@using (Html.BeginForm()) {@Html.ValidationSummary(true)<字段集><legend>MyModel</legend>@Html.EditorFor(m=>m.BaseClass,"DerievedView")<p><输入类型=提交"值=创建"/></p></fieldset>}

DerievedView.cshtml

@model [e-mail](true)<字段集><legend>MyDerievedClass</legend><div class="editor-label">@Html.LabelFor(model => model.MyProperty)

<div class="editor-field">@Html.EditorFor(model => model.MyProperty)@Html.ValidationMessageFor(model => model.MyProperty)

</fieldset>

现在它将按预期工作，Controller 将收到一个MyDerievedClass"类型的对象.验证将按预期进行.

Say I have a Product model, the Product model has a property of ProductSubType (abstract) and we have two concrete implementations Shirt and Pants.

Here is the source:

 public class Product
 {
    public int Id { get; set; }

    [Required]
    public string Name { get; set; }

    [Required]
    public decimal? Price { get; set; }

    [Required]
    public int? ProductType { get; set; }

    public ProductTypeBase SubProduct { get; set; }
}

public abstract class ProductTypeBase { }

public class Shirt : ProductTypeBase
{
    [Required]
    public string Color { get; set; }
    public bool HasSleeves { get; set; }
}

public class Pants : ProductTypeBase
{
    [Required]
    public string Color { get; set; }
    [Required]
    public string Size { get; set; }
}

In my UI, user has a dropdown, they can select the product type and the input elements are displayed according to the right product type. I have all of this figured out (using an ajax get on dropdown change, return a partial/editor template and re-setup the jquery validation accordingly).

Next I created a custom model binder for ProductTypeBase.

 public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
 {

        ProductTypeBase subType = null;

        var productType = (int)bindingContext.ValueProvider.GetValue("ProductType").ConvertTo(typeof(int));

        if (productType == 1)
        {
            var shirt = new Shirt();

            shirt.Color = (string)bindingContext.ValueProvider.GetValue("SubProduct.Color").ConvertTo(typeof(string));
            shirt.HasSleeves = (bool)bindingContext.ValueProvider.GetValue("SubProduct.HasSleeves").ConvertTo(typeof(bool));

            subType = shirt;
        }
        else if (productType == 2)
        {
            var pants = new Pants();

            pants.Size = (string)bindingContext.ValueProvider.GetValue("SubProduct.Size").ConvertTo(typeof(string));
            pants.Color = (string)bindingContext.ValueProvider.GetValue("SubProduct.Color").ConvertTo(typeof(string));

            subType = pants;
        }

        return subType;

    }
}

This binds the values correctly and works for the most part, except I lose the server side validation. So on a hunch that I am doing this incorrectly I did some more searching and came across this answer by Darin Dimitrov:

ASP.NET MVC 2 - Binding To Abstract Model

So I switched the model binder to only override CreateModel, but now it doesn't bind the values.

protected override object CreateModel(ControllerContext controllerContext, ModelBindingContext bindingContext, Type modelType)
    {
        ProductTypeBase subType = null;

        var productType = (int)bindingContext.ValueProvider.GetValue("ProductType").ConvertTo(typeof(int));

        if (productType == 1)
        {
            subType = new Shirt();
        }
        else if (productType == 2)
        {
            subType = new Pants();
        }

        return subType;
    }

Stepping though the MVC 3 src, it seems like in BindProperties, the GetFilteredModelProperties returns an empty result, and I think is because bindingcontext model is set to ProductTypeBase which doesn't have any properties.

Can anyone spot what I am doing wrong? This doesn't seem like it should be this difficult. I am sure I am missing something simple...I have another alternative in mind of instead of having a SubProduct property in the Product model to just have separate properties for Shirt and Pants. These are just View/Form models so I think that would work, but would like to get the current approach working if anything to understand what is going on...

Thanks for any help!

Update:

I didn't make it clear, but the custom model binder I added, inherits from the DefaultModelBinder

Answer

Setting ModelMetadata and Model was the missing piece. Thanks Manas!

protected override object CreateModel(ControllerContext controllerContext, ModelBindingContext bindingContext, Type modelType)
        {
            if (modelType.Equals(typeof(ProductTypeBase))) {
                Type instantiationType = null;

                var productType = (int)bindingContext.ValueProvider.GetValue("ProductType").ConvertTo(typeof(int));

                if (productType == 1) {
                    instantiationType = typeof(Shirt);
                }
                else if (productType == 2) {
                    instantiationType = typeof(Pants);
                }

                var obj = Activator.CreateInstance(instantiationType);
                bindingContext.ModelMetadata = ModelMetadataProviders.Current.GetMetadataForType(null, instantiationType);
                bindingContext.ModelMetadata.Model = obj;
                return obj;
            }

            return base.CreateModel(controllerContext, bindingContext, modelType);

        }

解决方案

This can be achieved through overriding CreateModel(...). I will demonstrate that with an example.

1. Lets create a model and some base and child classes.

public class MyModel
{
    public MyBaseClass BaseClass { get; set; }
}

public abstract class MyBaseClass
{
    public virtual string MyName
    {
        get
        {
            return "MyBaseClass";
        }
    }
}

public class MyDerievedClass : MyBaseClass
{

    public int MyProperty { get; set; }
    public override string MyName
    {
        get
        {
            return "MyDerievedClass";
        }
    }
}

2. Now create a modelbinder and override CreateModel

public class MyModelBinder : DefaultModelBinder
{
    protected override object CreateModel(ControllerContext controllerContext, ModelBindingContext bindingContext, Type modelType)
    {
        /// MyBaseClass and MyDerievedClass are hardcoded.
        /// We can use reflection to read the assembly and get concrete types of any base type
        if (modelType.Equals(typeof(MyBaseClass)))
        {
            Type instantiationType = typeof(MyDerievedClass);                
            var obj=Activator.CreateInstance(instantiationType);
            bindingContext.ModelMetadata = ModelMetadataProviders.Current.GetMetadataForType(null, instantiationType);
            bindingContext.ModelMetadata.Model = obj;
            return obj;
        }
        return base.CreateModel(controllerContext, bindingContext, modelType);
    }

}

3. Now in the controller create get and post action.

[HttpGet]
public ActionResult Index()
    {
        ViewBag.Message = "Welcome to ASP.NET MVC!";

        MyModel model = new MyModel();
        model.BaseClass = new MyDerievedClass();

        return View(model);
    }

    [HttpPost]
    public ActionResult Index(MyModel model)
    {

        return View(model);
    }

4. Now Set MyModelBinder as Default ModelBinder in global.asax This is done to set a default model binder for all actions, for a single action we can use ModelBinder attribute in action parameters)

protected void Application_Start()
    {
        AreaRegistration.RegisterAllAreas();

        ModelBinders.Binders.DefaultBinder = new MyModelBinder();

        RegisterGlobalFilters(GlobalFilters.Filters);
        RegisterRoutes(RouteTable.Routes);
    }

5. Now we can create view of type MyModel and a partial view of type MyDerievedClass

Index.cshtml

@model MvcApplication2.Models.MyModel

@{
ViewBag.Title = "Index";
Layout = "~/Views/Shared/_Layout.cshtml";
}

<h2>Index</h2>

@using (Html.BeginForm()) {
@Html.ValidationSummary(true)
<fieldset>
    <legend>MyModel</legend>
    @Html.EditorFor(m=>m.BaseClass,"DerievedView")
    <p>
        <input type="submit" value="Create" />
    </p>
</fieldset>
}

DerievedView.cshtml

@model MvcApplication2.Models.MyDerievedClass

@Html.ValidationSummary(true)
<fieldset>
    <legend>MyDerievedClass</legend>

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

</fieldset>

Now it will work as expected, Controller will receive an Object of type "MyDerievedClass". Validations will happen as expected.

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