ASP.Net Core MVC中的DataAnnotationsModelValidatorProvider.RegisterAdapter

Question

在ASP.Net MVC 5中，可以通过继承DataAnnotationsModelValidator并使用DataAnnotationsModelValidatorProvider.RegisterAdapter（...）进行注册来实现自定义数据注释验证器。在ASP.Net Core MVC中，我该如何实现这一目标？

我在ASP.net core MVC 6 Data Annotations separation of concerns发现了类似的问题，但有人能告诉我简单的示例代码吗？

Answer 1

在我看来，ASP.NET Core MVC不再支持DataAnnotationsModelValidatorProvider.RegisterAdapter了。我发现的解决方案如下：

假设我想将RequiredAttribute的Validator更改为我自己的验证器适配器（MyRequiredAttributeAdaptor），更改EmailAddressAttribute的默认错误消息，并将'CompareAttribute'的本地化错误消息源更改为我自己的消息。

1-创建自定义ValidationAttributeAdapterProvider

using Microsoft.AspNetCore.Mvc.DataAnnotations;
using Microsoft.AspNetCore.Mvc.DataAnnotations.Internal;
using Microsoft.Extensions.Localization;
using System.ComponentModel.DataAnnotations;

public class CustomValidationAttributeAdapterProvider
    : ValidationAttributeAdapterProvider, IValidationAttributeAdapterProvider
{
    public CustomValidationAttributeAdapterProvider() { }

    IAttributeAdapter IValidationAttributeAdapterProvider.GetAttributeAdapter(
        ValidationAttribute attribute,
        IStringLocalizer stringLocalizer)
    {
        IAttributeAdapter adapter;
        if (attribute is RequiredAttribute)
        {
            adapter = new MyRequiredAttributeAdaptor((RequiredAttribute) attribute, stringLocalizer);
        }
        else if (attribute is EmailAddressAttribute)
        {
            attribute.ErrorMessage = "Invalid Email Address.";
            adapter = base.GetAttributeAdapter(attribute, stringLocalizer);
        }
        else if (attribute is CompareAttribute)
        {
            attribute.ErrorMessageResourceName = "InvalidCompare"; 
            attribute.ErrorMessageResourceType = typeof(Resources.ValidationMessages);
            var theNewattribute = attribute as CompareAttribute;
            adapter = new CompareAttributeAdapter(theNewattribute, stringLocalizer);
        }
        else
        {
            adapter = base.GetAttributeAdapter(attribute, stringLocalizer);
        }

        return adapter;
    }
}

2-添加CustomValidationAttribute Adapter Provider以启动：

将以下行添加到Startup.cs中的public void ConfigureServices(IServiceCollection services)：

services.AddSingleton <IValidationAttributeAdapterProvider, CustomValidationAttributeAdapterProvider> ();

这是我的RequiredAttribute适配器适配器：

using System;
using System.ComponentModel.DataAnnotations;
using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
using Microsoft.Extensions.Localization;
using Microsoft.AspNetCore.Mvc.DataAnnotations.Internal;

public class MyRequiredAttributeAdaptor : AttributeAdapterBase<RequiredAttribute>
{
    public MyRequiredAttributeAdaptor(RequiredAttribute attribute, IStringLocalizer stringLocalizer)
        : base(attribute, stringLocalizer)
    {
    }

    public override void AddValidation(ClientModelValidationContext context)
    {
        if (context == null)
        {
            throw new ArgumentNullException(nameof(context));
        }

        MergeAttribute(context.Attributes, "data-val", "true");
        MergeAttribute(context.Attributes, "data-val-required", GetErrorMessage(context));
    }

    /// <inheritdoc />
    public override string GetErrorMessage(ModelValidationContextBase validationContext)
    {
        if (validationContext == null)
        {
            throw new ArgumentNullException(nameof(validationContext));
        }

        return GetErrorMessage(validationContext.ModelMetadata, validationContext.ModelMetadata.GetDisplayName());
    }
}

参考文献：

1-请参阅Microsoft的示例：Entropy项目：这是针对.NET Core的不同功能的一个很好的示例。在这个问题中：请参阅Mvc.LocalizationSample.Web示例中的MinLengthSixAttribute实现：

https://github.com/aspnet/Entropy/tree/dev/samples/Mvc.LocalizationSample.Web

2-为了查看属性适配器的工作原理，请参阅github上的asp.Microsoft.AspNetCore.Mvc.DataAnnotations：

https://github.com/aspnet/Mvc/tree/dev/src/Microsoft.AspNetCore.Mvc.DataAnnotations

Answer 2

要通过注释定义自定义验证器，您可以定义自己的类，该类派生自ValidationAttribute并覆盖IsValid方法。无需明确注册此类。

在此示例中，自定义验证属性用于仅接受奇数作为有效值。

public class MyModel
{
    [OddNumber]
    public int Number { get; set; }
}

public class OddNumberAttribute : ValidationAttribute
{
    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        try
        {
            var number = (int) value;
            if (number % 2 == 1)
                return ValidationResult.Success;
            else
                return new ValidationResult("Only odd numbers are valid.");
        }
        catch (Exception)
        {
            return new ValidationResult("Not a number.");
        }            
    }
}

第二种方法是Model类实现IValidatableObject。如果验证需要访问模型类的多个成员，那么这尤其有用。这是奇数验证器的第二个版本：

public class MyModel : IValidatableObject
{
    public int Number { get; set; }

    public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
    {
        if (Number % 2 == 0)
            yield return new ValidationResult(
                 "Only odd numbers are valid.", 
                 new [] {"Number"});
    }
}

您可以在https://docs.asp.net/en/latest/mvc/models/validation.html#custom-validation中找到有关自定义验证的更多信息。