DataAnnotationsModelBinder如何使用自定义ViewModel？

Question

我正在尝试使用DataAnnotationsModelBinder,以便在ASP.NET MVC中使用数据注释进行服务器端验证.

只要我的ViewModel只是一个具有直接属性的简单类,一切都可以正常工作

public class Foo
{
    public int Bar {get;set;}
}

然而,DataAnnotationsModelBinder导致一个NullReferenceException试图用一个复杂的时候ViewModel,如

public class Foo
{
    public class Baz
    {
        public int Bar {get;set;}
    }

    public Baz MyBazProperty {get;set;}
}

对于渲染多个LINQ实体的视图来说,这是一个很大的问题,因为我更喜欢使用ViewModel包含多个LINQ实体的自定义s而不是无类型的ViewData数组.

该DefaultModelBinder不会有这个问题,所以它似乎是一个错误DataAnnotationsModelBinder.这有什么解决方法吗？

编辑:一种可能的解决方法当然是在ViewModel类中公开子对象的属性,如下所示:

public class Foo
{
    private Baz myBazInstance;

    [Required]
    public string ExposedBar
    {
        get { return MyBaz.Bar; }
        set { MyBaz.Bar = value; }
    }

    public Baz MyBaz
    {
        get { return myBazInstance ?? (myBazInstance = new Baz()); }
        set { myBazInstance = value; }
    }

    #region Nested type: Baz

    public class Baz
    {
        [Required]
        public string Bar { get; set; }
    }

    #endregion
}

#endregion

但我宁愿不必编写所有这些额外的代码.对于DefaultModelBinder这样的hiearchies工作得很好,所以我想也DataAnnotationsModelBinder应该这样做.

第二次编辑:看起来这确实是一个错误DataAnnotationsModelBinder.但是,希望在下一个ASP.NET MVC框架版本发布之前可以解决这个问题.有关详细信息,请参阅此论坛帖子.

Answer 1

我今天遇到了同样的问题.就像你自己一样,我不会将我的View直接绑定到我的模型,而是使用一个中间的ViewDataModel类,它包含Model的一个实例以及我想发送给视图的任何参数/配置.

我最终修改BindProperty了DataAnnotationsModelBinder来绕过它NullReferenceException,我个人不喜欢只有绑定它们才有效(见下面的原因).

protected override void BindProperty(ControllerContext controllerContext,
                                         ModelBindingContext bindingContext,
                                         PropertyDescriptor propertyDescriptor) {
    string fullPropertyKey = CreateSubPropertyName(bindingContext.ModelName, propertyDescriptor.Name);

    // Only bind properties that are part of the request
    if (bindingContext.ValueProvider.DoesAnyKeyHavePrefix(fullPropertyKey)) {
        var innerContext = new ModelBindingContext() {
            Model = propertyDescriptor.GetValue(bindingContext.Model),
            ModelName = fullPropertyKey,
            ModelState = bindingContext.ModelState,
            ModelType = propertyDescriptor.PropertyType,
            ValueProvider = bindingContext.ValueProvider
        };

        IModelBinder binder = Binders.GetBinder(propertyDescriptor.PropertyType);
        object newPropertyValue = ConvertValue(propertyDescriptor, binder.BindModel(controllerContext, innerContext));
        ModelState modelState = bindingContext.ModelState[fullPropertyKey];
        if (modelState == null)
        {
            var keys = bindingContext.ValueProvider.FindKeysWithPrefix(fullPropertyKey);
            if (keys != null && keys.Count() > 0)
                modelState = bindingContext.ModelState[keys.First().Key];
        }
        // Only validate and bind if the property itself has no errors
        //if (modelState.Errors.Count == 0) {
            SetProperty(controllerContext, bindingContext, propertyDescriptor, newPropertyValue);
            if (OnPropertyValidating(controllerContext, bindingContext, propertyDescriptor, newPropertyValue)) {

                OnPropertyValidated(controllerContext, bindingContext, propertyDescriptor, newPropertyValue);
            }
        //}

        // There was an error getting the value from the binder, which was probably a format
        // exception (meaning, the data wasn't appropriate for the field)
        if (modelState.Errors.Count != 0) {
            foreach (var error in modelState.Errors.Where(err => err.ErrorMessage == "" && err.Exception != null).ToList()) {
                for (var exception = error.Exception; exception != null; exception = exception.InnerException) {
                    if (exception is FormatException) {
                        string displayName = GetDisplayName(propertyDescriptor);
                        string errorMessage = InvalidValueFormatter(propertyDescriptor, modelState.Value.AttemptedValue, displayName);
                        modelState.Errors.Remove(error);
                        modelState.Errors.Add(errorMessage);
                        break;
                    }
                }
            }
        }
    }
}

我也对它进行了修改,以便它始终绑定属性上的数据,无论它是否有效.这样我就可以将模型传递回视图,而无需将无效属性重置为null.

控制器摘录

[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Edit(ProfileViewDataModel model)
{
    FormCollection form = new FormCollection(this.Request.Form);
    wsPerson service = new wsPerson();
    Person newPerson = service.Select(1, -1);
    if (ModelState.IsValid && TryUpdateModel<IPersonBindable>(newPerson, "Person", form.ToValueProvider()))
    {
        //call wsPerson.save(newPerson);
    }
    return View(model); //model.Person is always bound no null properties (unless they were null to begin with)
}

我的Model类(Person)来自web服务,所以我不能直接将属性放在它们上面,我解决这个问题的方法如下:

嵌套DataAnnotations的示例

[Validation.MetadataType(typeof(PersonValidation))]
public partial class Person : IPersonBindable { } //force partial.

public class PersonValidation
{
    [Validation.Immutable]
    public int Id { get; set; }
    [Validation.Required]
    public string FirstName { get; set; }
    [Validation.StringLength(35)]
    [Validation.Required]
    public string LastName { get; set; }
    CategoryItemNullable NearestGeographicRegion { get; set; }
}

[Validation.MetadataType(typeof(CategoryItemNullableValidation))]
public partial class CategoryItemNullable { }

public class CategoryItemNullableValidation
{
    [Validation.Required]
    public string Text { get; set; }
    [Validation.Range(1,10)]
    public string Value { get; set; }
}

现在,如果我将表单字段绑定到[ViewDataModel.]Person.NearestGeographicRegion.Text&[ViewDataModel.]Person.NearestGeographicRegion.Value,ModelState开始正确验证它们,DataAnnotationsModelBinder也正确绑定它们.

这个答案不是决定性的,它是今天下午挠头的产物.它没有经过适当的测试,尽管它通过了Brian Wilson开始的项目中的单元测试以及我自己的大部分有限测试.为了真正关闭这个问题,我很想听听Brad Wilson对这个解决方案的看法.