Validate form before submit asp net core 2 0

Introduction

When with ASP.NET Core 2.0, it is often necessary to form data before submitting it to the server. This ensures that the data entered by the user is valid and meets the required criteria. In this article, we will explore different ways to validate forms in ASP.NET Core 2.0 and provide examples to illustrate the concepts.

Client-Side Validation

Client-side validation is performed on the client's browser using JavaScript. It provides immediate feedback to the user without making a round trip to the server. ASP.NET Core 2.0 supports client-side validation through the use of data annotations and the jQuery Validation plugin.

Data Annotations

Data annotations are attributes that can be applied to model properties to specify validation rules. These annotations are used by both client-side and server-side validation. Let's consider an example where we have a form with a required email field:


public class User
{
    [Required(ErrorMessage = "Email is required")]
    [EmailAddress(ErrorMessage = "Invalid email address")]
    public  Email { get; set; }
}

In the above example, the [Required] attribute specifies that the email field is required, and the [EmailAddress] attribute ensures that the entered value is a valid email address. These annotations will be used for both client-side and server-side validation.

jQuery Validation Plugin

The jQuery Validation plugin is a popular JavaScript that provides client-side validation capabilities. To enable client-side validation in ASP.NET Core 2.0, we need to the necessary JavaScript files and configure the validation rules. Let's see an example:


<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery-validate/1.19.2/jquery.validate.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery-validation-unobtrusive/3.2.12/jquery.validate.unobtrusive.min.js"></script>

In the above example, we include the necessary JavaScript files for the jQuery Validation plugin. These files are hosted on a CDN for convenience. Once the files are , the plugin will automatically handle the client-side validation based on the data annotations specified in the model.

Server-Side Validation

Server-side validation is performed on the server after the form is submitted. It is essential to perform server-side validation to ensure the integrity and security of the data. ASP.NET Core 2.0 provides built-in mechanisms to perform server-side validation.

ModelState Validation

The ModelState object in ASP.NET Core 2.0 contains the validation state of the model. It is automatically populated with validation errors during model binding. We can check the ModelState.IsValid property to determine if the form data is valid. Let's consider an example:


[]
public IActionResult SubmitForm(User user)
{
    if (!ModelState.IsValid)
    {
        // Handle invalid form data
         View(user);
    }
    
    // Process valid form data
    return RedirectToAction("");
}

In the above example, we check the ModelState.IsValid property to determine if the form data is valid. If it is not valid, we return the view with the invalid model so that the user can correct the errors. If the form data is valid, we can process it accordingly.

Conclusion

Validating forms before submitting them in ASP.NET Core 2.0 is crucial to ensure the integrity and security of the data. By using data annotations and the jQuery Validation plugin, we can perform client-side validation to provide immediate feedback to the user. Additionally, server-side validation using the ModelState object ensures that the data is valid before further . By combining these techniques, we can create robust and user-friendly form validation in ASP.NET Core 2.0.

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