ASP .Net Core 3.0 显示属性中的 ShortName (DataAnnotations)

Question

这个问题过去曾被问过，答案在这里 has been a life saver for me. The problem is that when I migrated to .Net Core 3.0, it broke. The reason can be found here https://github.com/aspnet/AspNetCore/issues/8678。简而言之，Microsoft 在标记为内部的 class 中创建了一些函数 public。解决此问题会删除对 ExpressionMetadataProvider 的访问权限。考虑以下 HTML Helper

using Microsoft.AspNetCore.Mvc.ViewFeatures.Internal;

public static class MvcHtmlHelpers
{
    private static IHtmlContent MetaDataFor<TModel, TValue>(this IHtmlHelper<TModel> html,
                                                            Expression<Func<TModel, TValue>> expression,
                                                            Func<ModelMetadata, string> property)
    {
        if (html == null) throw new ArgumentNullException(nameof(html));
        if (expression == null) throw new ArgumentNullException(nameof(expression));

        var modelExplorer = ExpressionMetadataProvider.FromLambdaExpression(expression, html.ViewData, html.MetadataProvider);
        if (modelExplorer == null) throw new InvalidOperationException($"Failed to get model explorer for {ExpressionHelper.GetExpressionText(expression)}");
        return new HtmlString(property(modelExplorer.Metadata));
    }

    public static IHtmlContent DescriptionFor<TModel, TValue>(this IHtmlHelper<TModel> html, Expression<Func<TModel, TValue>> expression)
    {
        return html.MetaDataFor(expression, m => m.Description ?? m.Name);
    }

    public static IHtmlContent ShortNameFor<TModel, TValue>(this IHtmlHelper<TModel> html,
        Expression<Func<TModel, TValue>> expression)
    {
        return html.MetaDataFor(expression, m =>
        {
            var defaultMetadata = m as
                Microsoft.AspNetCore.Mvc.ModelBinding.Metadata.DefaultModelMetadata;
            if (defaultMetadata != null)
            {
                var displayAttribute = defaultMetadata.Attributes.Attributes
                    .OfType<DisplayAttribute>()
                    .FirstOrDefault();
                if (displayAttribute != null)
                {
                    return displayAttribute.ShortName ?? m.DisplayName ?? m.Name;
                }
            }
            //Return a default value if the property doesn't have a DisplayAttribute
            return m.DisplayName ?? m.Name;
        });
    }
}

当您按照步骤迁移到.Net Core 3.0时，无法再解析ExpressionMetadataProvider和ExpressionHelper。

Answer 1

在 .Net Core 3.0 中，Microsoft 提供了一种使用依赖注入和名为 ModelExpressionProvider 的服务获取相同元数据的方法。您可以通过 IHtmlHelper 中的 HttpContext 访问该服务。只需将 using 替换为：

using Microsoft.AspNetCore.Mvc.ViewFeatures;

删除 .Internal，并将 MetaDataFor 函数替换为：

    private static IHtmlContent MetaDataFor<TModel, TValue>(this IHtmlHelper<TModel> html,
                                                            Expression<Func<TModel, TValue>> expression,
                                                            Func<ModelMetadata, string> property)
    {
        if (html == null) throw new ArgumentNullException(nameof(html));
        if (expression == null) throw new ArgumentNullException(nameof(expression));

        ModelExpressionProvider modelExpressionProvider = (ModelExpressionProvider)html.ViewContext.HttpContext.RequestServices.GetService(typeof(IModelExpressionProvider));

        var modelExplorer = modelExpressionProvider.CreateModelExpression(html.ViewData, expression);
        if (modelExplorer == null) throw new InvalidOperationException($"Failed to get model explorer for {modelExpressionProvider.GetExpressionText(expression)}");

        return new HtmlString(property(modelExplorer.Metadata));
    }

一旦 MetaDataFor 被修复以检索它们需要的内容，其他两个扩展函数将正常工作。

干杯！

ASP .Net Core 3.0 显示属性中的 ShortName (DataAnnotations)

ASP .Net Core 3.0 ShortName in the Display Attribute (DataAnnotations)

c#

asp.net-mvc

razor-pages

asp.net-core-3.0

.net-core-3.0