Why You Should Use Inheritance When Writing Django Models

When building a Django application, managing your models efficiently is key to maintaining clean, readable, and scalable code. One powerful yet often overlooked practice is using inheritance to streamline your models. By creating a BaseModel class and subclassing your models from it, you can effortlessly reuse common fields across all your models. In this blog post, we’ll dive into why this practice is essential and how to implement it effectively.

What is a BaseModel?

A BaseModel is a custom abstract model that serves as a foundation for all other models in your Django project. It encapsulates fields and functionality that are commonly needed across multiple models, such as:

• Tracking Creation and Updates: Fields like created_at, updated_at, and last_updated_by are often required to track when a record was created, modified, and who made the changes.
• User Associations: Adding a user field helps to tie records to specific users, making it easier to implement multi-tenancy or user-specific features.

By placing these fields in a BaseModel, you avoid repeating yourself across multiple models.

Why Use Inheritance in Django Models?

1. Avoid Redundancy: Without a BaseModel, you’d need to duplicate common fields in every model. This not only clutters your code but also increases the risk of inconsistencies.

2. Improved Maintainability: When a common field needs to be updated, such as adding constraints or altering its behavior, you can make the change in one place — the BaseModel. Every model that inherits from it will automatically reflect the change.

3. Consistency Across Models: Using inheritance ensures all models share the same implementation for shared fields. This minimizes bugs caused by varying implementations in different models.

4. DRY Principle: Django embraces the "Don't Repeat Yourself" (DRY) principle. Inheriting from a BaseModel aligns perfectly with this philosophy by reducing code duplication.

How to Create and Use a BaseModel

Here’s a step-by-step guide to implementing a BaseModel in Django:

1. Define the BaseModel

Create an abstract base class by setting abstract = True in the model’s Meta options. This ensures that Django won’t create a database table for the BaseModel itself.

from django.db import models  
from django.contrib.auth.models import User  

class BaseModel(models.Model):  
    created_at = models.DateTimeField(auto_now_add=True)  
    updated_at = models.DateTimeField(auto_now=True)  
    last_updated_by = models.ForeignKey(
        User, on_delete=models.SET_NULL, null=True, blank=True, related_name="%(class)s_last_updated_by"
    )  

    class Meta:  
        abstract = True

2. Subclass Your Models

Now, create your application-specific models by inheriting from the BaseModel.

class Product(BaseModel):  
    name = models.CharField(max_length=255)  
    price = models.DecimalField(max_digits=10, decimal_places=2)  

class Order(BaseModel):  
    order_number = models.CharField(max_length=100)  
    total_amount = models.DecimalField(max_digits=10, decimal_places=2)

3. Add Custom Behavior (Optional)

You can extend the BaseModel to include methods or properties that all models should have. For example, a method to format timestamps:

class BaseModel(models.Model):  
    created_at = models.DateTimeField(auto_now_add=True)  
    updated_at = models.DateTimeField(auto_now=True)  

    def get_formatted_created_at(self):  
        return self.created_at.strftime("%Y-%m-%d %H:%M:%S")  

    class Meta:  
        abstract = True

Tips for Using a BaseModel

1. Keep it Lean: Include only the fields and methods that are truly common across all models. Avoid adding application-specific fields or logic.

2. Use Descriptive Field Names: Use related_name in ForeignKeys like last_updated_by to avoid clashes when multiple models inherit from the BaseModel.

3. Document It: Add documentation to the BaseModel so team members understand its purpose and how to use it.

The Benefits in Action

Imagine you’re tasked with adding an archived_at field to every model. If you’re using a BaseModel, you can add this field in one place, and every model that subclasses it will inherit the new field automatically:

class BaseModel(models.Model):  
    created_at = models.DateTimeField(auto_now_add=True)  
    updated_at = models.DateTimeField(auto_now=True)  
    archived_at = models.DateTimeField(null=True, blank=True)  

    class Meta:  
        abstract = True

This approach saves hours of refactoring and reduces the likelihood of errors.

Conclusion

Using inheritance in Django models is a best practice that enhances code readability, maintainability, and consistency. By creating a BaseModel for your common fields and methods, you embrace the DRY principle, streamline your development process, and future-proof your application for changes.

Start implementing BaseModel in your projects today and experience the benefits of clean, scalable Django code!