如何仅为一个 Razor 页面设置 `ValidationVisitor.MaxValidationDepth` = 1？

Question

如何为一个 Razor 页面在本地更改 ValidationVisitor.MaxValidationDepth 以防止验证子对象？

我不想用MvcOptions.MaxValidationDepth 全局更改它，就像文档中描述的那样：Maximum recursion

这是一个后续问题。请查看我的原始问题以查看此处的对象结构：​

Razor Page validation error with a complex object, TryValidateModel() does not work

Answer 1

我们可以从IObjectModelValidator开始。默认实现是内部的 (DefaultObjectValidator) 并继承自 ObjectModelValidator。基（和抽象）类要求派生类只实现一种称为GetValidationVisitor 的方法。这是您在运行之前修改ValidationVisitor 的MaxValidationDepth 的一个扩展点。默认实现DefaultObjectValidator 只是将MaxValidationDepth 设置为从MvcOptions 获得的值。所以正如你所说，它在全球范围内应用。

在您对IObjectModelValidator 的自定义实现中（当然我们让它继承自ObjectModelValidator），您可以改为从当前上下文中获取MaxValidationDepth。

在执行每个页面处理程序之前，您可以设置您选择的MaxValidationDepth。为了使其成为标准（用作横切关注点），我们可以创建一个 IAsyncPageFilter 作为属性，该属性可以应用于您想要的任何页面模型类。

下面是实现代码：

//the custom IObjectModelValidator (which is much like what from the source code 
//of DefaultObjectValidator)
public class ContextBasedObjectModelValidator : ObjectModelValidator
{
    readonly MvcOptions _mvcOptions;
    public ContextBasedObjectModelValidator(IModelMetadataProvider modelMetadataProvider, 
                                            IList<IModelValidatorProvider> validatorProviders,
                                            MvcOptions mvcOptions) : base(modelMetadataProvider, validatorProviders)
    {
        _mvcOptions = mvcOptions;
    }

    public override ValidationVisitor GetValidationVisitor(ActionContext actionContext, 
        IModelValidatorProvider validatorProvider, 
        ValidatorCache validatorCache, 
        IModelMetadataProvider metadataProvider, 
        ValidationStateDictionary validationState)
    {            
        var visitor = new ValidationVisitor(
            actionContext,
            validatorProvider,
            validatorCache,
            metadataProvider,
            validationState)
        {
            MaxValidationDepth = actionContext.HttpContext.Features.Get<IContextBasedMaxValidationDepthFeature>()?.MaxValidationDepth ?? _mvcOptions.MaxValidationDepth,
            ValidateComplexTypesIfChildValidationFails = _mvcOptions.ValidateComplexTypesIfChildValidationFails,
        };

        return visitor;
    }
}

//we need a class for the custom request feature to hold your context-based MaxValidationDepth
public interface IContextBasedMaxValidationDepthFeature
{
    int MaxValidationDepth { get; }
}
public class ContextBasedMaxValidationDepthFeature : IContextBasedMaxValidationDepthFeature
{
    public ContextBasedMaxValidationDepthFeature(int maxValidationDepth)
    {
        MaxValidationDepth = maxValidationDepth;
    }
    public int MaxValidationDepth { get; }
}

//here the page filter to help set your context-based MaxValidationDepth
[AttributeUsage(AttributeTargets.Class)]
public class MaxValidationDepthAttribute : Attribute, IAsyncPageFilter
{
    public MaxValidationDepthAttribute(int maxValidationDepth)
    {
        MaxValidationDepth = maxValidationDepth;
    }
    public int MaxValidationDepth { get; }
    public Task OnPageHandlerExecutionAsync(PageHandlerExecutingContext context, PageHandlerExecutionDelegate next)
    {
        //set the max validation depth from the predefined value (via the attribute)
        context.HttpContext.Features
               .Set<IContextBasedMaxValidationDepthFeature>(new ContextBasedMaxValidationDepthFeature(MaxValidationDepth));
        return next();
    }

    public Task OnPageHandlerSelectionAsync(PageHandlerSelectedContext context)
    {
        return Task.CompletedTask;
    }
}

最后我们需要在Startup.ConfigureServices中注册你的自定义IObjectModelValidator：

services.Replace(new ServiceDescriptor(typeof(IObjectModelValidator), sp => {
            var options = sp.GetRequiredService<IOptions<MvcOptions>>().Value;
            var metadataProvider = sp.GetRequiredService<IModelMetadataProvider>();
            return new ContextBasedObjectModelValidator(metadataProvider, options.ModelValidatorProviders, options);
        }, ServiceLifetime.Singleton));

使用它：

//suppose you want it to be 1
//for this specific page
[MaxValidationDepth(1)]
public class YourPageModel : PageModel {
     //...
}