String Length Validation

StringLengthValidation.cshtml.cs

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

namespace WorkStandard.Pages.validation
{
    public class StringLengthValidationModel : PageModel
    {
        [BindProperty]
        [DisplayName("Student ID")]
        [StringLength(8, ErrorMessage = "{0} must be within {1} characters")]
        public string? studentId { get; set; }

        public void OnPost()
        {
            //Server side validation check
            if (!ModelState.IsValid)
            {
                return;
            }

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

→ Where Debug.WriteLine outputs to

StringLengthValidation.cshtml

@page
@model WorkStandard.Pages.validation.StringLengthValidationModel

<form method="post">
    <div class="mb-3">
        <label asp-for="studentId"></label>
        <input asp-for="studentId" class="form-control" />
        <span asp-validation-for="studentId" 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");
    }
}

Note: As in this example, you must check validation result at server side. Malicious users can easily bypass client side validation to attack the server.

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

Note： In this sample, The meaning of the number of Characters is same as result of String.Length. If you are not familiar with this see String Length .

Note: To test input over 8 characters, add maxlength="100" explicitly to the input element.

StringMinLengthValidation.cshtml.cs

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

namespace WorkStandard.Pages.validation
{
    public class StringMinLengthValidationModel : PageModel
    {
        [BindProperty]
        [DisplayName("Student ID")]
        [Required(ErrorMessage = "{0} is required.")]
        [StringLength(8, MinimumLength = 3, ErrorMessage = "{0} must be between {2} and {1} characters.")]
        public string? studentId { get; set; }

        public void OnPost()
        {
            //Server side validation check
            if (!ModelState.IsValid)
            {
                return;
            }

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

→ Where Debug.WriteLine outputs to

StringMinLengthValidation.cshtml

@page
@model WorkStandard.Pages.validation.StringMinLengthValidationModel

<form method="post">
    <div class="mb-3">
        <label asp-for="studentId"></label>
        <input asp-for="studentId" class="form-control" />
        <span asp-validation-for="studentId" 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");
    }
}

Note: As in this example, you must check validation result at server side. Malicious users can easily bypass client side validation to attack the server.

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

Note： In this sample, The meaning of the number of Characters is same as result of String.Length. If you are not familiar with this see String Length .

Note: To test input over 8 characters, add maxlength="100" explicitly to the input element.