c# - 如何在 ASP.NET Core 中本地化验证属性的标准错误消息

Question

如何本地化 ASP.NET Core (v2.2) 中验证属性的标准错误消息？例如，[Required]属性有这个错误信息“ The xxx field is required. ”；[EmailAddress]有“ xxx 字段不是有效的电子邮件地址。 ”；【比较】有“ ‘xxx’和‘yyy’不匹配。 ”等等。在我们的项目中，我们不使用英语，我想找到一种方法来翻译标准错误消息，而无需将它们直接写入每个数据模型类的每个属性中

标签： c#asp.net-core-2.2validationattributeasp.net-core-localization

Answer 1

如果您只想本地化错误消息而不是构建多语言站点，您可以试试这个：（消息字符串可能是您的语言。）

1. 添加自定义IValidationMetadataProvider：

    public class MyModelMetadataProvider : IValidationMetadataProvider
    {
        public void CreateValidationMetadata(ValidationMetadataProviderContext context)
        {
            if (context == null)
            {
                throw new ArgumentNullException();
            }
            var validators = context.ValidationMetadata.ValidatorMetadata;

            // add [Required] for value-types (int/DateTime etc)
            // to set ErrorMessage before asp.net does it
            var theType = context.Key.ModelType;
            var underlyingType = Nullable.GetUnderlyingType(theType);

            if (theType.IsValueType &&
                underlyingType == null && // not nullable type
                validators.Where(m => m.GetType() == typeof(RequiredAttribute)).Count() == 0)
            {
                validators.Add(new RequiredAttribute());
            }
            foreach (var obj in validators)
            {
                if (!(obj is ValidationAttribute attribute))
                {
                    continue;
                }
                fillErrorMessage<RequiredAttribute>(attribute, 
                    "You must fill in '{0}'.");
                fillErrorMessage<MinLengthAttribute>(attribute, 
                    "Min length of '{0}' is {1}.");
                fillErrorMessage<MaxLengthAttribute>(attribute, 
                    "Max length of '{0}' is {1}.");
                fillErrorMessage<EmailAddressAttribute>(attribute, 
                    "Invalid email address.", true);
                // other attributes like RangeAttribute, CompareAttribute, etc
            }
        }
        private void fillErrorMessage<T>(object attribute, string errorMessage, 
            bool forceOverriding = false) 
            where T : ValidationAttribute
        {
            if (attribute is T validationAttribute)
            {
                if (forceOverriding ||
                    (validationAttribute.ErrorMessage == null 
                    && validationAttribute.ErrorMessageResourceName == null))
                {
                    validationAttribute.ErrorMessage = errorMessage;
                }
            }
        }
    }

2. 在中添加一些行Startup.cs：

        public void ConfigureServices(IServiceCollection services)
        {
            services.AddControllersWithViews()
                .AddMvcOptions(m => {
                    m.ModelMetadataDetailsProviders.Add(new MyModelMetadataProvider());

                    m.ModelBindingMessageProvider.SetValueMustBeANumberAccessor(
                        fieldName => string.Format("'{0}' must be a valid number.", fieldName));
                    // you may check the document of `DefaultModelBindingMessageProvider`
                    // and add more if needed

                })
                ;
        }

查看DefaultModelBindingMessageProvider 的文档

如果您可以用日语阅读，请参阅本文了解更多详细信息。