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

我该如何改变ValidationVisitor.MaxValidationDepth在本地为一个 Razor 页面阻止验证子对象？

我不想在全球范围内改变它MvcOptions.MaxValidationDepth就像文档中描述的那样：最大递归 https://learn.microsoft.com/en-us/aspnet/core/mvc/models/validation?view=aspnetcore-5.0#maximum-recursion

这是一个跟随问题。请检查我原来的问题以查看此处的对象结构：​

复杂对象的 Razor 页面验证错误，TryValidateModel() 不起作用 https://stackoverflow.com/q/67348699/248756

我们可以从IObjectModelValidator。默认实现是内部的（DefaultObjectValidator）并继承自ObjectModelValidator。基（和抽象）类要求派生类仅实现一种称为GetValidationVisitor。这是您修改的一个扩展点MaxValidationDepth of the ValidationVisitor在它运行之前。默认实现DefaultObjectValidator只是设置MaxValidationDepth到获得的值MvcOptions。所以正如你所说，它在全球范围内应用。

在您的自定义实现中IObjectModelValidator（当然我们让它继承自ObjectModelValidator），可以得到MaxValidationDepth相反，从当前上下文。

在执行每个页面处理程序之前，您可以设置MaxValidationDepth你的选择。为了使其成为标准（像横切关注点一样使用），我们可以创建一个IAsyncPageFilter作为可以应用于您想要的任何页面模型类的属性。

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;
    }
}

最后我们需要注册您的自定义IObjectModelValidator在 - 的里面Startup.ConfigureServices:

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));

Use it:

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