How to Localize validation message (DataAnnotationsValidator) in blazor server side

Question

I am using blazor 3.1 in latest version of VS 2019.

So far, I am able to localize page labels (title, table fields etc.).

On the ListEmployee.razor page, I am able to localize table heading etc. On the AddEmplyeeValidation.razor page, I am able to localize form labels but I have a problem localizing the validation messages.

For validation message for the Employee.cs file, validation message are defined in the Resources/Data folder in files Data.Employee.resx and Data.Employee.ar.resx but this doesn't seem to work.

    using System.ComponentModel.DataAnnotations;

    namespace BlazorSPA1.Data
    {
        public class Employee
        {
            [MaxLength(50)]
            public string Id { get; set; }

            [Required (ErrorMessage ="Name is RRRequired")]
            [StringLength(20, ErrorMessage = "Name is too long.")]
            public string Name { get; set; }

            [Required]
            [StringLength(20)]
            public string Department { get; set; }
            [MaxLength(100)]
            public string Designation { get; set; }
            [MaxLength(100)]
            public string Company { get; set; }
            [MaxLength(100)]
            public string City { get; set; }
        }
    }

How can I load the validation messages from the resource files based on language for my AddEmployeForm?

    @page "/addemployeeValidation"
    @inject NavigationManager NavigationManager
    @inject IEmployeeService EmployeeService
    @inject IStringLocalizer<AddEmployeeValidation> L

    <h2>Create Employee</h2>
    <hr />
    <EditForm Model="@employee" OnValidSubmit="@CreateEmployee">
        <DataAnnotationsValidator />
        <ValidationSummary />
        <div class="row">
            <div class="col-md-8">
                <div class="form-group">
                    <label for="Name" class="control-label">@L["Name"]</label>
                    <input for="Name" class="form-control" @bind="@employee.Name" />
                    <ValidationMessage For="@(()=> employee.Name)" />
                </div>
                <div class="form-group">
                    <label for="Department" class="control-label">@L["Department"]</label>
                    <input for="Department" class="form-control" @bind="@employee.Department" />
                </div>
                <div class="form-group">
                    <label for="Designation" class="control-label">@L["Designation"]</label>
                    <input for="Designation" class="form-control" @bind="@employee.Designation" />
                </div>
                <div class="form-group">
                    <label for="Company" class="control-label">@L["Company"]</label>
                    <input for="Company" class="form-control" @bind="@employee.Company" />
                </div>
                <div class="form-group">
                    <label for="City" class="control-label">@L["City"]</label>
                    <input for="City" class="form-control" @bind="@employee.City" />
                </div>
            </div>
        </div>
        <div class="row">
            <div class="col-md-4">
                <div class="form-group">
                    <input type="submit" class="btn btn-primary" value="Save" />
                    <input type="button" class="btn" @onclick="@Cancel" value="Cancel" />
                </div>
            </div>
        </div>
    </EditForm>

    @code {

        Employee employee = new Employee();

        protected async Task CreateEmployee()
        {
            await EmployeeService.CreateEmployee(employee);
            NavigationManager.NavigateTo("listemployees");
        }


        void Cancel()
        {
            NavigationManager.NavigateTo("listemployees");
        }
    }   

I have read a few articles and tried few thing but nothing seems to be working.

Here is my Startup.cs code:

        services.AddServerSideBlazor(options => options.DetailedErrors = true);
        services.AddLocalization(options => options.ResourcesPath = "Resources");
        var supportedCultures = new List<CultureInfo> { new CultureInfo("en"), new CultureInfo("ar") };
        services.Configure<RequestLocalizationOptions>(options =>
        {
            options.DefaultRequestCulture = new Microsoft.AspNetCore.Localization.RequestCulture("en");
            options.SupportedUICultures = supportedCultures;
        });

I am using the following example for localization but it doesn't show how to localize error messages: https://www.c-sharpcorner.com/article/localization-in-blazor-server/

Folder structure image for reference:

Resource file example for English version in same way i have Arabic file also:

In the screenshot below, you will see field names are being pulled correctly from the Resource file but validation messages are not working and only display in English.

Answer 1

Here is my solution for localizing data annotation error messages. I create two resource files, one for fields and another one for error messages.

• DisplayNameResource for localizing fields
• ErrorMessageResource for localizing error messages

In view model class use Display attribute for localizing field name. To specify resource file use ResourceType property on Display attribute:

[Display(Name = "Address", ResourceType = typeof(DisplayNameResource))]

And on validation attributes use ErrorMessageResourceName and ErrorMessageResourceType to specify resource file:

[Required(ErrorMessageResourceName = "RequiredError", ErrorMessageResourceType = typeof(ErrorMessageResource))]

Here is full example:

public class SomeViewModel
{
    [Display(Name = "Address", ResourceType = typeof(DisplayNameResource))]
    [Required(ErrorMessageResourceName = "RequiredError", ErrorMessageResourceType = typeof(ErrorMessageResource))]
    [StringLength(256, ErrorMessageResourceName = "MaxLengthError", ErrorMessageResourceType = typeof(ErrorMessageResource))]
    public string Address { get; set; }

    [Display(Name = "Phone", ResourceType = typeof(DisplayNameResource))]
    [Required(ErrorMessageResourceName = "RequiredError", ErrorMessageResourceType = typeof(ErrorMessageResource))]
    [RegularExpression("^09([0-9]{9})$", ErrorMessageResourceName = "PhoneLengthError", ErrorMessageResourceType = typeof(ErrorMessageResource))]
    public string Phone { get; set; }

    [Display(Name = "Password", ResourceType = typeof(DisplayNameResource))]
    [Required(ErrorMessageResourceName = "RequiredError", ErrorMessageResourceType = typeof(ErrorMessageResource))]
    [StringLength(50, MinimumLength = 6, ErrorMessageResourceType = typeof(ErrorMessageResource), ErrorMessageResourceName = "MinxMaxLengthError")]
    public string Password { get; set; }

    [Display(Name = "ConfirmPassword", ResourceType = typeof(DisplayNameResource))]
    [Required(ErrorMessageResourceName = "RequiredError", ErrorMessageResourceType = typeof(ErrorMessageResource))]
    [StringLength(50, MinimumLength = 6, ErrorMessageResourceType = typeof(ErrorMessageResource), ErrorMessageResourceName = "MinxMaxLengthError")]
    [Compare("Password", ErrorMessageResourceName = "PasswordConfirmMisMatch", ErrorMessageResourceType = typeof(ErrorMessageResource))]
    public string ConfirmPassword { get; set; }
}

Error message for MaxLengthError is {0} cannot be longer than {1} character, so {0} will be replaced with localized filed name and {1} will be replaced with the 256 you specified on attribute [StringLength(256,...

Answer 2

This has been asked before:

How to add ViewModel localization to Blazor?

I suggested that using FluentValidation would be a better approach. Here is a link to my Github repo that demonstrates how it could work:

https://github.com/conficient/BlazorValidationLocalization