Validate alphanumeric characters (by regular expression)

RegexAlphaNumeric.cshtml.cs

using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;
using System.ComponentModel;
using System.ComponentModel.DataAnnotations;

namespace WorkStandard.Pages.validation
{
    public class RegexAlphaNumericModel : PageModel
    {
        [BindProperty]
        [DisplayName("Model ID")]
        [RegularExpression("[0-9a-zA-Z]*",ErrorMessage = "The {0} must be alphanumeric characters.")]
        public string? ModelNumber { get; set; }

            public void OnPost()
            {
                if (!ModelState.IsValid)
                {
                    return;
                }

            System.Diagnostics.Debug.WriteLine($"No errors.{ModelNumber}");
        }
    }
}

→ Where Debug.WriteLine outputs to

RegexAlphaNumeric.cshtml

@page
@model WorkStandard.Pages.validation.RegexAlphaNumericModel

<form method="post">
    <div class="mb-3">
        <label asp-for="ModelNumber"></label>
        <input asp-for="ModelNumber" class="form-control" />
        <span asp-validation-for="ModelNumber" class="text-danger"></span>
    </div>
    <div>
        <input type="submit" class="btn btn-primary" />
    </div>
</form>

@section Scripts {
    @{
        //Enable client side validation
        await Html.RenderPartialAsync("_ValidationScriptsPartial");
    }
}

The CSS classes...

• mb-3 Set little margin at bottom.→ Spacing
• form-control Make the input a Bootstrap look.→ Forms
• text-danger The string become red to indicate danger.→ Theme colors
• btn btn-primary Give the button a Bootstrap look to indicate that it's a key feature.→ Buttons