In this article I will explain with an example, how to perform Password and Confirm Password validation on Server Side using Data Annotation attributes in ASP.Net Core Razor Pages.
The Data Annotation attributes will be applied to the Model class properties in ASP.Net Core Razor Pages.
 
 
Model
The following Model class consists of two properties Password and ConfirmPassword. The properties are decorated with the following Data Annotation attributes for performing validations.
1. Required Data Annotation attribute.
2. Compare Data Annotation attribute. In this case Password.
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 Compare 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 first parameter of the Compare attribute has been set with the name of the property with which the value needs to be compared i.e. Password.
using System.ComponentModel.DataAnnotations;
 
namespace Compare_Password_Validation_Server_Side_Razor_Core.Models
{
    public class PersonModel
    {
        [Required(ErrorMessage = "Password is required.")]
        public string Password { get; set; }
 
        [Required(ErrorMessage = "Confirmation Password is required.")]
        [Compare("Password", ErrorMessage = "Password and Confirmation Password must match.")]
        public string ConfirmPassword { get; set; }
    }
}
 
 
Razor PageModel (Code-Behind)
The PageModel consists of following two Handler methods.
Handler method for handling GET operation
This Handler method handles the GET calls, for this particular example it is not required and hence left empty.
 
Handler method for handling POST operation
This Handler method handles the POST operation and when the form is submitted, the object of the PersonModel class is sent to this method.
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.
 
public class IndexModel : PageModel
{
    public PersonModel Person { get; set; }
    public void OnGet()
    {
    }
 
    public void OnPostSubmit(PersonModel person)
    {
        ViewData["Password"] = person.Password;
        ViewData["ConfirmPassword"] = person.ConfirmPassword;
        if (ModelState.IsValid)
        {
            // Validation success.
 
            ViewData["Password"] = string.Empty;
            ViewData["ConfirmPassword"] = string.Empty;
        }
    }
}
 
 
Razor Page (HTML)
The Form
The HTML of Razor Page consists of an HTML Form which has been created using following ASP.Net Tag Helpers attribute.
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 two HTML INPUT Password TextBoxes, two SPAN elements and a Submit Button.
The Password and the ConfirmPassword TextBoxes have been set with the following Tag Helpers attributes:-
asp-for – The Model property to which validation will be performed. In this case Password and ConfirmPassword.
asp-validation-for - Displaying the validation message for the Model property.
The Submit Button has been set with the POST Handler method using the asp-page-handler attribute. When the Submit button is clicked, the Form gets submitted and the Model is sent to the Handler method.
Note: In the Razor PageModel, the Handler method name is OnPostSubmit but here it will be specified as Submit when calling from the Razor HTML Page.
 
@page
@model Compare_Password_Validation_Server_Side_Razor_Core.Pages.IndexModel
@addTagHelper*, Microsoft.AspNetCore.Mvc.TagHelpers
@{
    Layout = null;
}
 
<!DOCTYPE html>
 
<html>
<head>
    <meta name="viewport" content="width=device-width" />
    <title>Index</title>
    <style type="text/css">
        body { font-family: Arial; font-size: 10pt; }
        .error { color: red; }
    </style>
</head>
<body>
    <form method="post">
        <table>
            <tr>
                <td>Password</td>
                <td><input type="password" asp-for="Person.Password" value="@ViewData["Password"]" /></td>
                <td><span asp-validation-for="Person.Password" class="error"></span></td>
            </tr>
            <tr>
                <td>Confirm Password</td>
                <td><input type="password" asp-for="Person.ConfirmPassword" value="@ViewData["ConfirmPassword"]" /></td>
                <td><span asp-validation-for="Person.ConfirmPassword" class="error"></span></td>
            </tr>
            <tr>
                <td></td>
                <td><input type="submit" value="Submit" asp-page-handler="Submit" /></td>
                <td></td>
            </tr>
        </table>
    </form>
</body>
</html>
 
 
Screenshot

ASP.Net Core Razor Pages: Server Side Password and Confirm Password validation using Data Annotations

 
 
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