How to apply Remote Validations in ASP.NET MVC?. The Complete ASP.NET MVC Developer Course 2023 [Videos].

In this article, I am going to discuss Remote Validations in ASP.NET MVC applications. Please read our previous article where we discussed Validation Message and Validation Summary Attribute in ASP.NET MVC Application. At the end of this article, you will understand what is Remote Validation and why we need this and how to implement Remote Validations in ASP.NET MVC applications.

What is Remote Validation in ASP.NET MVC Application?

Sometimes, to check if a field value is valid or not, we may need to make a database call. A classic example of this is the Gmail user registration page. To register a user, we need a unique username. So, to check, if the username is not taken already, we have to make a call to the server and check the database table. RemoteAttribute is useful in situations like this. So in this Video, I am going to discuss how to use Remote Validations in ASP.NET MVC Application.

Example: When a user provides a username that already exists, the associated validation error message should be displayed immediately as shown below. 

 Step 1: Create Users table

Step2: Create one ASP.NET MVC application with the name “RemoteValidationInMVC”

Step3:Create an ado.net entity data model using table Users. Save and build the solution.

It will create the following model

Step4: Add HomeController with the following settings

1. Template = MVC5 controller with views, using Entity Framework
2. Model Class = User (RemoteValidationInMVC.Models)
3. Data context class = UserDBContext (RemoteValidationInMVC.Models)
4. Controller Name = HomeController

Step5: 

Copy and paste the following function in HomeController. This is the method that gets called to perform the remote validation. An AJAX request is issued to this method. If this method returns true, validation succeeds, else validation fails and the form is prevented from being submitted. The parameter name (UserName) must match the field name on the view. If they dont match, the model binder will not be able to bind the value with the parameter, and validation may not work as expected.

Step6:

Right-click on the Models folder and a class file with the name PUser.cs. Copy and paste the following code. Notice that the name of the method (IsUserNameAvailable) and the controller name (Home) and the error message are passed as arguments to Remote Attribute. Remote is the attribute for validation in Data Annotation, which is used in model class to validate records instantly.

In the above example, we have defined a few properties of the Remote attribute to work on remote validation properly, lets know them in brief.

1. IsUserNameAvailable: This is the JsonResult method which checks the details from the database and returns true or false.
2. Home: This is the MVC Controller name and inside that, the IsUserNameAvailable JsonResult method is defined to check the details from the database.
3. HttpMethod: This is the HttpMethod type which is called on Remote attribute e.g. Get, Put, Post. This is optional to define.
4. ErrorMessage: This is used to show the message on the client-side. 

There are many optional properties of the Remote attribute which are used as per the validation requirements.

Step7:

Include references to the following CSS and script files in Create.cshtml view. jquery.validate and jquery.validate.unobtrusive script files are required for remote validation to work.

Step8:

Make sure ClientValidation and UnobtrusiveJavaScript are enabled in web.config

<add key=”ClientValidationEnabled” value=”true” />
<add key=”UnobtrusiveJavaScriptEnabled” value=”true” /> 

Run the application and see everything is working as expected. The remote attribute only works when JavaScript is enabled. If the end-user disables JavaScript on his/her machine then the validation does not work.