In this article I will explain with an example, how to perform Mobile Number (Cellphone Number) validation for TextBox i.e. exact Ten Numbers (Digits) validation on Client Side using Data Annotation in ASP.Net Core MVC.
Note: For beginners in ASP.Net Core (.Net Core 7), please refer my article ASP.Net Core 7: Hello World Tutorial with Sample Program example.
 
The Mobile Phone Number (Cellphone Number) validation will be performed using Regular Expression (Regex).
 
 

Model

The following Model class consists of one property MobileNumber. The property is decorated with the following Data Annotation attributes for performing validations.
1. Required Data Annotation attribute.
2. RegularExpression Data Annotation attribute.
Note: The Data Annotations attributes can be used with the Entity Data Model (EDM), LINQ to SQL, and other data models.
 
The Required Data Annotation and the RegularExpression Data Annotation attributes have been specified with a property Error Message with a string value. As the name suggests, this string value will be displayed to the user when the respective validation fails.
The RegularExpression Data Annotation attribute has been set with a Regular Expression for validating Mobile Phone Number (Cellphone Number).
using System.ComponentModel.DataAnnotations;
 
namespace MobileNumber_Validation_MVC_Core.Models
{
    public class PersonModel
    {
        [Display(Name = "Mobile Number:")]
        [Required(ErrorMessage = "Mobile Number is required.")]
        [RegularExpression("^([0-9]{10})$", ErrorMessage = "Invalid Mobile Number.")]
        public string MobileNumber { get; set; }
    }
}
 
 

Controller

The Controller consists of following Action methods.

Action method for handling GET operation

Inside this Action method, simply the View is returned.
 

Action method for handling POST operation

This Action method handles the POST operation and when the form is submitted.
The state of the submitted Model is checked using ModelState.IsValid property.
Note: ModelState.IsValid property is an inbuilt property which verifies two things:
          1. Whether the Form values are bound to the Model.
          2. All the validations specified inside Model class using Data annotations have been passed.
 
Finally, the View is returned to Index View.
public class HomeController : Controller
{
    public IActionResult Index()
    {
        return View();
    }
 
    [HttpPost]
    public IActionResult Validate()
    {
        if (ModelState.IsValid)
        {
            // Validation Success.
        }
 
        return View("Index");
    }
}
 
 

View

HTML Markup

Inside the View, in the very first line the PersonModel class is declared as Model for the View.
 

The Form

The View consists of an HTML Form which has been created using following ASP.Net Tag Helpers attributes.
asp-action – Name of the Action. In this case the name is Validate.
asp-controller – Name of the Controller. In this case the name is Home.
method – It specifies the Form Method i.e. GET or POST. In this case it will be set to POST.
 

Implementing Validation

The Form consists of a Label, an HTML INPUT TextBox, a SPAN element and a Submit Button.
The TextBox has been set with the following Tag Helpers attributes:-
asp-for – The Model property to which validation will be performed. In this case MobileNumber.
asp-validation-for – Displaying the validation message for the Model property.
When the Submit Button is clicked, the Form gets submitted and the TextBox value i.e. MobileNumber is sent to the Controller.
 

Enabling Client-Side validations

The default validation performed on server side when one uses Data Annotations along with Model class for validation purpose.
In order to enable Client-Side validations, you need to inherit the following script files.
1. jquery.min.js
2. jquery.validate.js
3. jquery.validate.unobtrusive.js
Once, the above files are inherited, the Client-Side validations using Data Annotations is enabled.
@model MobileNumber_Validation_MVC_Core.Models.PersonModel
@addTagHelper*, Microsoft.AspNetCore.Mvc.TagHelpers
@{
    Layout = null;
}
 
<!DOCTYPE html>
 
<html>
<head>
    <meta name="viewport" content="width=device-width" />
    <title>Index</title>
</head>
<body>
    <form method="post" asp-controller="Home" asp-action="Validate">
        <table>
            <tr>
                <td><label asp-for="MobileNumber"></label></td>
                <td><input type="text" asp-for="MobileNumber" /></td>
                <td><span asp-validation-for="MobileNumber" class="error"></span></td>
            </tr>
            <tr>
                <td></td>
                <td><input type="submit" value="Submit" /></td>
                <td></td>
            </tr>
        </table>
    </form>
 
    <script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.7.1/jquery.min.js"></script>
    <script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/jquery-validate/1.19.3/jquery.validate.js"></script>
    <scripttype="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/jquery-validation-unobtrusive/3.2.12/jquery.validate.unobtrusive.js"></script>
</body>
</html>
 
 

Screenshot

ASP.Net Core MVC: Mobile Number (Cellphone Number) Validation using Data Annotations
 
 

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