Multi-lingual support for default messages displayed during input validation

environment

ASP.NET Core

• 5.0 MVC

At first

The multilingual support of the default input validation messages with this Tips may not be complete. Please deal with the missing ones.

Also, changing the language depending on the session state or cache state may still appear in text from the previous language.

There are several ways to change the default input validation message, each of which can be combined. It is not one of them, so if you want to change it reliably, you need to correspond with all patterns.

premise

This Tips is written as understanding the following tips:

• ASP.NET The built-in features of Core MVC for multi-lingual switching
• Multi-lingual support for DataAnnotations used for parameter names, input validation messages, etc.

Also, if you are creating a new project, you must have added the following files and code based on tips above.

• Create a SharedResource.resx (+en, es) file. (Since only the message of this Tips is translated, the contents may be empty.)
• Create a SharedResource.cs file
• Add localization code to Startup.ConfigureServices
• Add localization code to Startup.Configure
• Added UserViewModel (this time, we don't explicitly key the default messages in multiple languages)
• Added user-created screen actions and views (Create.cshtml)

Starting code

Based on the above assumptions, each code shall be as follows:

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Localization;
using Microsoft.AspNetCore.Mvc.Razor;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using System.Globalization;

namespace LocalizationDefaultValidation
{
  public class Startup
  {
    // 省略

    public void ConfigureServices(IServiceCollection services)
    {
      services.AddControllersWithViews();

      services.AddMvc()
        // ローカライズに必要。Resx ファイルのフォルダパスを指定
        .AddViewLocalization(LanguageViewLocationExpanderFormat.Suffix, opts => { opts.ResourcesPath = "Resources"; })
        // DataAnnotations のローカライズに必要
        .AddDataAnnotationsLocalization(options =>
        {
          // DataAnnotation を使ったときのメッセージは SharedResource に集約する
          options.DataAnnotationLocalizerProvider = (type, factory) => factory.Create(typeof(SharedResource));
        });
    }

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
      if (env.IsDevelopment())
      {
        app.UseDeveloperExceptionPage();
      }
      else
      {
        app.UseExceptionHandler("/Home/Error");
        // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
        app.UseHsts();
      }

      // 標準の機能で切り替えたい言語を定義します。
      var supportedCultures = new[]
      {
        new CultureInfo("ja"),
        new CultureInfo("en"),
        new CultureInfo("es"),
      };

      // 標準の言語切り替え機能を有効にします。対応しているのは「クエリ文字列」「Cookie」「Accept-Language HTTP ヘッダー」です。
      app.UseRequestLocalization(new RequestLocalizationOptions
      {
        DefaultRequestCulture = new RequestCulture("ja"),
        SupportedCultures = supportedCultures,
        SupportedUICultures = supportedCultures
      });

      app.UseHttpsRedirection();
      app.UseStaticFiles();

      // 省略
    }
  }
}

using LocalizationDefaultValidation.Models;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.Extensions.Logging;
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Threading.Tasks;

namespace LocalizationDefaultValidation.Controllers
{
  public class HomeController : Controller
  {
    // 省略

    public IActionResult Create()
    {
      SetDayOfWeeksViewData();
      return View();
    }

    [HttpPost]
    public IActionResult Create(UserViewModel model)
    {
      SetDayOfWeeksViewData();

      // エラーなら差し戻し
      if (ModelState.IsValid == false) return View(model);

      // 正常に登録できた場合は Index に戻る
      return RedirectToAction(nameof(Index));
    }

    /// <summary>曜日の一覧を ViewData に設定します。</summary>
    private void SetDayOfWeeksViewData()
      => ViewData["DayOfWeeks"] = ((DayOfWeek[])Enum.GetValues(typeof(DayOfWeek))).Select(x => new SelectListItem(x.ToString(), ((int)x).ToString()));
  }
}

@{
  ViewData["Title"] = "Home Page";
}

<div class="text-center">
  <h1 class="display-4">Welcome</h1>
  <p>Learn about <a href="https://docs.microsoft.com/aspnet/core">building Web apps with ASP.NET Core</a>.</p>
</div>

<p>ユーザー作成画面に遷移します。リンクごとに選択した言語で表示できます。</p>
<ul>
  <li><a asp-action="Create">Create</a></li>
  <li><a asp-action="Create" asp-route-culture="ja">Create (ja)</a></li>
  <li><a asp-action="Create" asp-route-culture="en">Create (en)</a></li>
  <li><a asp-action="Create" asp-route-culture="es">Create (es)</a></li>
</ul>

@model LocalizationDefaultValidation.Models.UserViewModel
@using System.Globalization;
@{
  ViewData["Title"] = "Create";
}

<h1>Create</h1>

<h4>UserViewModel</h4>
<hr />
<div class="row">
  <div class="col-md-4">
    <form asp-action="Create" enctype="multipart/form-data" >
      <div asp-validation-summary="ModelOnly" class="text-danger"></div>
      <div class="form-group">
        <label asp-for="ID" class="control-label"></label>
        <input asp-for="ID" class="form-control" />
        <span asp-validation-for="ID" class="text-danger"></span>
      </div>
      <div class="form-group">
        <label asp-for="Name" class="control-label"></label>
        <input asp-for="Name" class="form-control" />
        <span asp-validation-for="Name" class="text-danger"></span>
      </div>
      <div class="form-group">
        <label asp-for="Password" class="control-label"></label>
        <input asp-for="Password" class="form-control" />
        <span asp-validation-for="Password" class="text-danger"></span>
      </div>
      <div class="form-group">
        <label asp-for="ConfirmPassword" class="control-label"></label>
        <input asp-for="ConfirmPassword" class="form-control" />
        <span asp-validation-for="ConfirmPassword" class="text-danger"></span>
      </div>
      <div class="form-group">
        <label asp-for="Email" class="control-label"></label>
        <input asp-for="Email" class="form-control" />
        <span asp-validation-for="Email" class="text-danger"></span>
      </div>
      <div class="form-group">
        <label asp-for="Age" class="control-label"></label>
        <input asp-for="Age" class="form-control" />
        <span asp-validation-for="Age" class="text-danger"></span>
      </div>
      <div class="form-group">
        <label asp-for="Gender"></label>
        <div>
          <label><input type="radio" asp-for="Gender" value="@(GenderType.None)" />@(GenderType.None)</label>
          <label><input type="radio" asp-for="Gender" value="@(GenderType.Man)" />@(GenderType.Man)</label>
          <label><input type="radio" asp-for="Gender" value="@(GenderType.Woman)" />@(GenderType.Woman)</label>
        </div>
        <span asp-validation-for="Gender" class="text-danger"></span>
      </div>
      <div class="form-group">
        <label asp-for="Birthday" class="control-label"></label>
        <input asp-for="Birthday" class="form-control" />
        <span asp-validation-for="Birthday" class="text-danger"></span>
      </div>
      <div class="form-group">
        <label asp-for="Phone" class="control-label"></label>
        <input asp-for="Phone" class="form-control" />
        <span asp-validation-for="Phone" class="text-danger"></span>
      </div>
      <div class="form-group">
        <label asp-for="PostalCode" class="control-label"></label>
        <input asp-for="PostalCode" class="form-control" />
        <span asp-validation-for="PostalCode" class="text-danger"></span>
      </div>
      <div class="form-group">
        <label asp-for="CreditCard" class="control-label"></label>
        <input asp-for="CreditCard" class="form-control" />
        <span asp-validation-for="CreditCard" class="text-danger"></span>
      </div>
      <div class="form-group">
        <label asp-for="Money" class="control-label"></label>
        <input asp-for="Money" class="form-control" />
        <span asp-validation-for="Money" class="text-danger"></span>
      </div>
      <div class="form-group">
        <label asp-for="StartDateTime" class="control-label"></label>
        <input asp-for="StartDateTime" class="form-control" />
        <span asp-validation-for="StartDateTime" class="text-danger"></span>
      </div>
      <div class="form-group">
        <label asp-for="WakeUpTime" class="control-label"></label>
        <input asp-for="WakeUpTime" class="form-control" />
        <span asp-validation-for="WakeUpTime" class="text-danger"></span>
      </div>
      <div class="form-group">
        <label asp-for="Homepage" class="control-label"></label>
        <input asp-for="Homepage" class="form-control" />
        <span asp-validation-for="Homepage" class="text-danger"></span>
      </div>
      <div class="form-group">
        <label asp-for="MyImage" class="control-label"></label>
        <input asp-for="MyImage" class="form-control" />
        <span asp-validation-for="MyImage" class="text-danger"></span>
      </div>
      <div class="form-group">
        <label asp-for="MyColor" class="control-label"></label>
        <input asp-for="MyColor" class="form-control" type="color" />
        <span asp-validation-for="MyColor" class="text-danger"></span>
      </div>
      <div class="form-group">
        <label asp-for="WorkingDays" class="control-label"></label>
        <select asp-for="WorkingDays" class="form-control" asp-items="@((IEnumerable<SelectListItem>)ViewData["DayOfWeeks"])" multiple></select>
        <span asp-validation-for="WorkingDays" class="text-danger"></span>
      </div>
      <div class="form-group">
        <label asp-for="VacationDay" class="control-label"></label>
        <select asp-for="VacationDay" class="form-control" asp-items="@((IEnumerable<SelectListItem>)ViewData["DayOfWeeks"])" multiple></select>
        <span asp-validation-for="VacationDay" class="text-danger"></span>
      </div>
      <div class="form-group">
        <label asp-for="Comment" class="control-label"></label>
        <textarea asp-for="Comment" class="form-control"></textarea>
        <span asp-validation-for="Comment" class="text-danger"></span>
      </div>
      <div class="form-group">
        <label asp-for="FileName" class="control-label"></label>
        <input asp-for="FileName" class="form-control" />
        <span asp-validation-for="FileName" class="text-danger"></span>
      </div>
      <div class="form-group">
        <label asp-for="UploadFile" class="control-label"></label>
        <input asp-for="UploadFile" type="file" multiple />
        <span asp-validation-for="UploadFile" class="text-danger"></span>
      </div>
      <div class="form-group">
        <label asp-for="Month" class="control-label"></label>
        <input asp-for="Month" class="form-control" type="month" />
        <span asp-validation-for="Month" class="text-danger"></span>
      </div>
      <div class="form-group">
        <label asp-for="Search" class="control-label"></label>
        <input asp-for="Search" class="form-control" type="search" />
        <span asp-validation-for="Search" class="text-danger"></span>
      </div>
      <div class="form-group">
        <label asp-for="Range" class="control-label"></label>
        <input asp-for="Range" class="form-control" type="range" min="10" max="100" />
        <span asp-validation-for="Range" class="text-danger"></span>
      </div>
      <div class="form-group">
        <label asp-for="Week" class="control-label"></label>
        <input asp-for="Week" class="form-control" type="week" />
        <span asp-validation-for="Week" class="text-danger"></span>
      </div>
      <div class="form-group form-check">
        <label class="form-check-label">
          <input class="form-check-input" asp-for="IsAccepted" /> @Html.DisplayNameFor(model => model.IsAccepted)
        </label>
      </div>
      <div class="form-group">
        <input type="submit" value="Create" class="btn btn-primary" asp-route-culture="@CultureInfo.CurrentCulture.Name" />
      </div>
    </form>
  </div>
</div>

<div>
  <a asp-action="Index">Back to List</a>
</div>

@section Scripts {
  @{await Html.RenderPartialAsync("_ValidationScriptsPartial");}
}

using Microsoft.AspNetCore.Http;
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;

namespace LocalizationDefaultValidation.Models
{
  public class UserViewModel
  {
    [Required]
    [Display(Name = "ID (半角英数字)")]
    [StringLength(20)]
    [RegularExpression(@"^[0-9a-zA-Z]*$")]
    public string ID { get; set; }

    [StringLength(50)]
    public string Name { get; set; }

    [StringLength(50, MinimumLength = 8)]
    [DataType(DataType.Password)]
    [RegularExpression(@"^[0-9a-zA-Z]*$")]
    public string Password { get; set; }

    [StringLength(50, MinimumLength = 8)]
    [DataType(DataType.Password)]
    [Compare(nameof(Password))]
    public string ConfirmPassword { get; set; }

    [EmailAddress]
    [DataType(DataType.EmailAddress)] // スキャフォールディングするときはコメントアウトする
    public string Email { get; set; }

    //[Int]
    [Range(0, 150)]
    public int Age { get; set; }

    [Required]
    [EnumDataType(typeof(GenderType))]
    public GenderType Gender { get; set; }

    [DataType(DataType.Date)]
    public DateTime Birthday { get; set; }

    [Phone()]
    [DataType(DataType.PhoneNumber)] // スキャフォールディングするときはコメントアウトする
    public string Phone { get; set; }

    [DataType(DataType.PostalCode)]
    public string PostalCode { get; set; }

    [CreditCard()]
    [DataType(DataType.CreditCard)] // スキャフォールディングするときはコメントアウトする
    public string CreditCard { get; set; }

    [DataType(DataType.Currency)]
    public decimal Money { get; set; }

    [DataType(DataType.DateTime)]
    public DateTime StartDateTime { get; set; }

    [DataType(DataType.Time)]
    public TimeSpan WakeUpTime { get; set; }

    [Url]
    [DataType(DataType.Url)] // スキャフォールディングするときはコメントアウトする
    public string Homepage { get; set; }

    [Url]
    [DataType(DataType.ImageUrl)] // スキャフォールディングするときはコメントアウトする
    public string MyImage { get; set; }

    public string MyColor { get; set; }

    [MaxLength(5)]
    public DayOfWeek[] WorkingDays { get; set; }

    [MinLength(3)]
    public DayOfWeek[] VacationDay { get; set; }

    [StringLength(200)]
    [DataType(DataType.MultilineText)]
    public string Comment { get; set; }

    [Display(Name = "ファイル名 (.png)")]
    [FileExtensions(Extensions = "png")]
    public string FileName { get; set; }

    [DataType(DataType.Upload)]
    public List<IFormFile> UploadFile { get; set; }

    public DateTime Month { get; set; }

    public string Search { get; set; }

    [Range(10, 100)]
    public int Range { get; set; }

    public string Week { get; set; }

    [Required]
    public bool IsAccepted { get; set; }
  }

  public enum GenderType
  {
    None,
    Man,
    Woman,
    Other,
  }
}

namespace LocalizationDefaultValidation
{
  // クラス名は作成した .resx のファイル名と同じにする必要がある
  public class SharedResource { }
}

Model binding messages

If you set the model property type int to or and bind it to the DateTime view, and try to register it untyped, you will see a message like "The value '' is invalid.". These messages appear when an empty string int cannot be bound to, for example, in the model. Because it is a timing that cannot be bound, it occurs only before other value validation and server-side processing.

These messages are DefaultModelBindingMessageProvider defined as .

Startup.cs Add to the arguments of the method that have been defined since the beginning services.AddControllersWithViews in , and then add Action . You can be multilingual by setting the passed in the options ModelBindingMessageProvider argument.

There are 11 types of messages that you can set, so you must first define the message in as follows: SharedResource.resx The name of the key is optional. The default English message in the comments column is (comments don't have to be included). You won't have to translate each language, so you should do your own translation (the sample code also includes the translated SharedResource.resx).

Fix startup.cs as follows:

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Localization;
using Microsoft.AspNetCore.Mvc.Razor;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Localization;
using System;
using System.Globalization;
using System.Reflection;

namespace LocalizationDefaultValidation
{
  public class Startup
  {
    // 省略 (初期コード)

    /// <summary>
    /// 検証メッセージローカライズで使用。
    /// </summary>
    private IServiceProvider ServiceProvider { get; set; }

    private IStringLocalizer _localizer = null;
    /// <summary>
    /// 検証メッセージローカライズで使用。
    /// </summary>
    private IStringLocalizer Localizer
      => _localizer ?? (_localizer = ServiceProvider.GetService<IStringLocalizerFactory>()
               .Create(nameof(SharedResource), new AssemblyName(typeof(SharedResource).Assembly.FullName).Name));

    // このメソッドはランタイムによって呼び出されます。 このメソッドを使用して、コンテナーにサービスを追加します。
    public void ConfigureServices(IServiceCollection services)
    {
      services.AddControllersWithViews(options =>
      {
        // 検証メッセージのローカライズで使用
        // モデルバインディング失敗時のエラーメッセージをカスタマイズ
        // サーバ側でモデルに値を格納する際に発生する可能性がある
        
        // メッセージの {0} や {1} を置換するための関数を定義
        static string f1(string f, string a1) => string.Format(f, a1);
        static string f2(string f, string a1, string a2) => string.Format(f, a1, a2);

        // 各メソッドを読んでメッセージを置き換えます
        var mp = options.ModelBindingMessageProvider;
        mp.SetAttemptedValueIsInvalidAccessor((x, y) => f2(Localizer["ModelBinding_AttemptedValueIsInvalid"], x, y));
        mp.SetMissingBindRequiredValueAccessor((x) => f1(Localizer["ModelBinding_MissingBindRequiredValue"], x));
        mp.SetMissingKeyOrValueAccessor(() => Localizer["ModelBinding_MissingKeyOrValue"]);
        mp.SetMissingRequestBodyRequiredValueAccessor(() => Localizer["ModelBinding_MissingRequestBodyRequiredValue"]);
        mp.SetNonPropertyAttemptedValueIsInvalidAccessor((x) => f1(Localizer["ModelBinding_NonPropertyAttemptedValueIsInvalid"], x));
        mp.SetNonPropertyUnknownValueIsInvalidAccessor(() => Localizer["ModelBinding_NonPropertyUnknownValueIsInvalid"]);
        mp.SetNonPropertyValueMustBeANumberAccessor(() => Localizer["ModelBinding_NonPropertyValueMustBeANumber"]);
        mp.SetUnknownValueIsInvalidAccessor((x) => f1(Localizer["ModelBinding_UnknownValueIsInvalid"], x));
        mp.SetValueIsInvalidAccessor((x) => f1(Localizer["ModelBinding_ValueIsInvalid"], x));
        mp.SetValueMustBeANumberAccessor((x) => f1(Localizer["ModelBinding_ValueMustBeANumber"], x));
        mp.SetValueMustNotBeNullAccessor((x) => f1(Localizer["ModelBinding_ValueMustNotBeNull"], x));
      });

      services.AddMvc()
        // ローカライズに必要。Resx ファイルのフォルダパスを指定
        .AddViewLocalization(LanguageViewLocationExpanderFormat.Suffix, opts => { opts.ResourcesPath = "Resources"; })
        // DataAnnotations のローカライズに必要
        .AddDataAnnotationsLocalization(options =>
        {
          // DataAnnotation を使ったときのメッセージは SharedResource に集約する
          options.DataAnnotationLocalizerProvider = (type, factory) => factory.Create(typeof(SharedResource));
        });
    }

    // このメソッドはランタイムによって呼び出されます。 このメソッドを使用して、HTTP要求パイプラインを構成します。
    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
      // ローカライズで使用するため IServiceProvider をプロパティに保持しておきます。
      ServiceProvider = app.ApplicationServices;

      // 標準の機能で切り替えたい言語を定義します。
      var supportedCultures = new[]
      {
        new CultureInfo("ja"),
        new CultureInfo("en"),
        new CultureInfo("es"),
      };

      // 標準の言語切り替え機能を有効にします。対応しているのは「クエリ文字列」「Cookie」「Accept-Language HTTP ヘッダー」です。
      app.UseRequestLocalization(new RequestLocalizationOptions
      {
        DefaultRequestCulture = new RequestCulture("ja"),
        SupportedCultures = supportedCultures,
        SupportedUICultures = supportedCultures
      });

      // 省略 (初期コード)
    }
  }
}

The key point is services.AddControllersWithViews to add a to the method that receives the option Action , options.ModelBindingMessageProvider I'm setting localized text for each Set method in .

The translated text is IStringLocalizer retrieved from . There is no way to receive direct IStringLocalizer code, which is a bit of a round code. SharedResource.resx If you're generating code from, you'll get localized values directly from it.

IStringLocalizer The key that you specify in SharedResource.resx specifies the key that you added to . Set it to match the contents of each Set method.

Also, because each message has a format string argument, such as , I {0}{1} use Simple with so that you can replace the received string.Format Func values.

Localize default validation messages

The default error message when the attributes of Required a model's properties are set to or so is determined by the framework and is StringLength basically in English.

These can be IValidationAttributeAdapterProvider localized by defining a class derived from the interface.

First of SharedResource.resx all, register the text that is multilingual. The name of the key is arbitrary, but to simplify the program, register it in the form of "Validator_< validation attribute name>".

Next, create the following AdapterProvider class:

The class name is arbitrary, but this time CustomValidationAttributeAdapterProvider I'll write a class called and write the code as follows: The location of the code file is arbitrary, but the sample is placed in a folder called Adapter.

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

namespace LocalizationDefaultValidation
{
  public class CustomValidationAttributeAdapterProvider : IValidationAttributeAdapterProvider
  {
    /// <summary>コード簡略化のためのリソースキー命名規則プリフィックス</summary>
    private const string RESOURCE_KEY_PREFIX = "Validator_";

    private readonly IValidationAttributeAdapterProvider _fallback = new ValidationAttributeAdapterProvider();

    /// <summary>
    /// 指定された ValidationAttribute の IAttributeAdapter を返します。
    /// </summary>
    /// <param name="attribute">IAttributeAdapter を作成するための ValidationAttribute。</param>
    /// <param name="stringLocalizer">メッセージの作成に使用される IStringLocalizer。</param>
    /// <returns>指定された属性の IAttributeAdapter。</returns>
    IAttributeAdapter IValidationAttributeAdapterProvider.GetAttributeAdapter(ValidationAttribute attribute, IStringLocalizer stringLocalizer)
    {
      // すでにエラーメッセージが設定されている場合はそれを使用するのでここでは何も設定しない
      if (attribute.ErrorMessageResourceName != null) return _fallback.GetAttributeAdapter(attribute, stringLocalizer);

      // attribute には「Required」や「StringLength」などが設定されています
      Type attrType = attribute.GetType();
      
      // プリフィックスと属性のクラス名からローカライズ用のキーを生成します
      var key = RESOURCE_KEY_PREFIX + attrType.Name;

      // IStringLocalizer から指定したキーでローカライズされたテキストを取得します
      // ない場合は getString にそのまま key の値が入ります
      var getString = stringLocalizer[key];

      // 正しくローカライズされたテキストが取得できた場合は ErrorMessage に値をセットします。
      if (key != getString && attribute.ErrorMessage != getString)
      {
        attribute.ErrorMessage = getString;
      }

      // 設定した attribute を渡します
      return _fallback.GetAttributeAdapter(attribute, stringLocalizer);
    }
  }
}

If you set the properties of the model to Required or , the method is called for every StringLength IValidationAttributeAdapterProvider.GetAttributeAdapter validation.

ErrorMessageResourceName If the property contains a value, the code on the model side already has a message or localization key, so it returns as it is.

If empty, match the class names of the prefix and validation attribute to make it the localization key, and then retrieve the localized text from the key and set it ErrorMessage to . This allows most of the default messages to be localized.

Next, register this class in startup .cs. Basically, you can add it as follows.

// 省略

using Microsoft.AspNetCore.Mvc.DataAnnotations;

namespace LocalizationDefaultValidation
{
  public class Startup
  {
    // 省略

    // このメソッドはランタイムによって呼び出されます。 このメソッドを使用して、コンテナーにサービスを追加します。
    public void ConfigureServices(IServiceCollection services)
    {
      // 省略

      // 作成した CustomValidationAttributeAdapterProvider をシングルトンとして登録します
      services.AddSingleton<IValidationAttributeAdapterProvider, CustomValidationAttributeAdapterProvider>();
    }
    
    // 省略
  }
}

Run it to make sure it's working properly.

Change an existing message by parameters

For example, StringLength the attribute message is localized, such as "{0} must be within {1} digits." MinimumLength If the property is set, you may want to change the {0} as "Specify {2} digits or more {1} within a number of digits".

In that CustomValidationAttributeAdapterProvider case, extend the class as follows:

// 省略

namespace LocalizationDefaultValidation
{
  public class CustomValidationAttributeAdapterProvider : IValidationAttributeAdapterProvider
  {
    // 省略

    IAttributeAdapter IValidationAttributeAdapterProvider.GetAttributeAdapter(ValidationAttribute attribute, IStringLocalizer stringLocalizer)
    {
      if (attribute is StringLengthAttribute slAttribute)
      {
        // attribute が StringLengthAttribute で MinimumLength が設定されている場合はメッセージを変える
        if (slAttribute.MinimumLength >= 1)
        {
          attribute.ErrorMessage = stringLocalizer["Validator_StringLengthAttributeWithMin"];
          return _fallback.GetAttributeAdapter(slAttribute, stringLocalizer);
        }
      }

      // 省略
    }
  }
}

Because the method is called for each GetAttributeAdapter validation, if the variable passed attribute was StringLengthAttribute an MinimumLength attribute, check the property, If set, get a message that also takes into account the minimum number of digits and ErrorMessage replaces .

If you run it, check and the message changes, it's OK.

Other generic messages

Some messages are not localized after you do so far. For example, messages that are determined only in Javascript.

The target is jquery.validate.js the message listed in the file.

Because this file should not be edited directly, to replace these messages with localized text, you input must add an attribute like to the tag and set data-val-XXXX localized text there. The XXXX part contains the key in the figure jquery.validate.js above. (e.g. data-val-number etc.)

data-val-XXXX To set localized text to attributes in

Let's localize the message when non-numeric characters are included in the Age input field as an example. UserViewModel.Age has Range an attribute, and the output HTML data-val-range appends the input attribute.

<div class="form-group">
  <label class="control-label" for="Age">Age</label>
  <input class="form-control" type="number" data-val="true" data-val-range="Ageは0から150の範囲で指定してください。" data-val-range-max="150" data-val-range-min="0" data-val-required="Ageは必須です。" id="Age" name="Age" value="" />
  <span class="text-danger field-validation-valid" data-valmsg-for="Age" data-valmsg-replace="true"></span>
</div>

However, data-val-number the numeric check message is not localized because there is no attribute. You'll add another attribute on the model side to print the localized message-added data-val-number attribute as well.

The first step is to create an attribute class that checks if it is IntAttribute a number: It is limited to here, but you are int free to change it depending on the situation. The code file can be anywhere, but this time it's in the Adapter folder.

using System.ComponentModel.DataAnnotations;

namespace LocalizationDefaultValidation
{
  public class IntAttribute : ValidationAttribute
  {
    public override bool IsValid(object value)
    {
      // 渡された値が int であれば有効な値とする
      return value is int;
    }
  }
}

If the set value is int a type, it is an attribute that is only a normal verdict, but in practice it is 100% normal if set to a property of type int, so the processing of this class itself does not make any sense. The purpose of this time is to display localized error messages in the client.

Next, create the following Adapter IntAttributeAdapter class: This is also in the Adapter folder.

using Microsoft.AspNetCore.Mvc.DataAnnotations;
using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
using Microsoft.Extensions.Localization;

namespace LocalizationDefaultValidation
{
  /// <summary>Int 属性のアダプター。</summary>
  public class IntAttributeAdapter : AttributeAdapterBase<IntAttribute>
  {
    /// <summary>受け取った IStringLocalizer を保持しておく</summary>
    IStringLocalizer _stringLocalizer;

    public IntAttributeAdapter(IntAttribute attribute, IStringLocalizer stringLocalizer)
        : base(attribute, stringLocalizer)
    {
      _stringLocalizer = stringLocalizer;
    }

    /// <summary>バリデーションの追加処理として呼ばれる。</summary>
    public override void AddValidation(ClientModelValidationContext context)
    {
      // 新たに data-val-number 属性をマージして追加します。値はローカライズしたテキストをセットします。
      MergeAttribute(context.Attributes, "data-val-number", _stringLocalizer["ModelBinding_NonPropertyValueMustBeANumber"]);
    }

    /// <summary>サーバーのエラーメッセージはそのまま返します。</summary>
    public override string GetErrorMessage(ModelValidationContextBase validationContext) => Attribute.ErrorMessage;
  }
}

The point here is AddValidation the method described in the MergeAttribute method.

Merging attributes as attributes of the input tag to return data-val-number to the client. The value to set in the attribute sets a localized error message.

Return this adapter in the class you created CustomValidationAttributeAdapterProvider earlier.

// 省略

namespace LocalizationDefaultValidation
{
  public class CustomValidationAttributeAdapterProvider : IValidationAttributeAdapterProvider
  {
    // 省略
    
    IAttributeAdapter IValidationAttributeAdapterProvider.GetAttributeAdapter(ValidationAttribute attribute, IStringLocalizer stringLocalizer)
    {
      // IntAttribute の場合は IntAttributeAdapter 経由で返す
      if (attribute is IntAttribute intAttribute)
      {
        return new IntAttributeAdapter(intAttribute, stringLocalizer);
      }

      // 省略 (前に追加したコード)
    }
  }
}

If the value to validate IntAttribute is , return the that you created IntAttributeAdapter earlier. The property with the Int attribute is now added when it is displayed on the client data-val-number side.

Finally, UserViewModel.Age IntAttribute add to .

Once you've fixed your code, try it out to see if you want to check it out.

<div class="form-group">
  <label class="control-label" for="Age">Age</label>
  <input class="form-control" type="number" data-val="true" data-val-number="数字を指定してください。" data-val-range="Ageは0から150の範囲で指定してください。" data-val-range-max="150" data-val-range-min="0" data-val-required="Ageは必須です。" id="Age" name="Age" value="" />
  <span class="text-danger field-validation-valid" data-valmsg-for="Age" data-valmsg-replace="true"></span>
</div>

There are other non-localized messages, but you can localize them in the methods described above. Add code when you need it.