Python Django How to do object level custom validations in the models

Title: How to Perform Object-Level Custom Validations in Django Models
Introduction:
In Django, you can perform object-level custom validations in your models to ensure that data adheres to your specific business rules before it gets saved to the database. This tutorial will guide you through the process of creating custom validation methods for your models using Python and Django. We'll cover the basics of object-level validation and provide a code example to illustrate the concept.
Prerequisites:
Step 1: Create a Django Model
To start, create a Django model or use an existing one. For this tutorial, let's assume we have a simple model called Book:
Step 2: Define a Custom Validation Method
Next, define a custom validation method within your model class. This method should raise a ValidationError when the object doesn't meet your validation criteria. For instance, we want to ensure that the publication year is not in the future.
In this example, we use the clean method, which is a built-in hook for model validation. We check if the publication_year is greater than the current year (using timezone.now().year) and raise a ValidationError if the condition is met.
Step 3: Using the Custom Validation
When you attempt to save an object that violates the custom validation rules, Django will raise a ValidationError. You can handle this error in your views or forms to provide user-friendly feedback.
Here's how you might handle the validation in a view: