Django’s Flexible Backend Support – How Django Web Application Uses Different Databases

A Django web application can work with multiple databases such as SQLite, PostgreSQL, MySQL, Oracle, MS SQL Server, or even MongoDB (with third-party support).

Django uses a component called Database Backend (DB engine) configured in settings.py to communicate with different database systems.

ORM (Object Relational Mapping)

In Django, ORM stands for Object-Relational Mapping. It’s a powerful feature that allows developers to interact with the database using Python code instead of SQL.

ORM is a layer that translates Python objects (like classes and attributes) to database tables and columns, and vice versa.

Instead of writing raw SQL queries, you define models in Python, and Django ORM handles all the SQL behind the scenes.

How Django ORM Works

Define Models (Python Classes)

• You create models in models.py using Django’s Model class.
• Each model represents a table, and each attribute becomes a column.

from django.db import models

class Book(models.Model):
    title = models.CharField(max_length=100)
    author = models.CharField(max_length=100)

Migrations (Translate Models to SQL)

• Django generates SQL code to create the actual database schema.

python manage.py makemigrations
python manage.py migrate

Querying with Python

• Instead of writing SQL, you use model methods to perform CRUD operations.

# Create
Book.objects.create(title="Geetha", author="Vyasadeva")

# Read
books = Book.objects.all()

# Update
book = Book.objects.get(id=1)
book.title = "Bhagavad Gita"
book.save()

# Delete
book.delete()

Database Abstraction

• You can switch between databases (e.g., SQLite, PostgreSQL, MySQL) without changing your model code.
• Just update the DATABASES setting in settings.py.

When you call:

Book.objects.filter(author="Vyasa")

Django internally translates it to:

SELECT * FROM book WHERE author = 'Vyasa';

Handles all execution and result conversion automatically.

Django uses ORM, so your model code is the same regardless of the backend:

class Book(models.Model):
    title = models.CharField(max_length=100)
    author = models.CharField(max_length=100)

You don’t change the model when switching databases.

Architecture

Switching Databases

To switch databases:

1. Install required adapter.
2. Change ENGINE in settings.py.
3. Update credentials.
4. Run migrate.

No need to change your models or views.

Step-by-Step Process

Step 1: Install Django and the Required Database Driver

For SQLite – Built-in with Python. No installation needed.

For PostgreSQL – Install psycopg2:

pip install psycopg2

For MySQL – Install mysqlclient:

pip install mysqlclient

For MS SQL Server – Use third-party backend like django-mssql-backend:

pip install django-mssql-backend

For Oracle – Install cx_Oracle:

pip install cx_Oracle

For MongoDB – Use third-party ORM like djongo or mongoengine:

pip install djongo

Step 2: Configure DATABASES in settings.py

SQLite

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': BASE_DIR / "db.sqlite3",
    }
}

PostgreSQL:

DATABASES = {
'default': {
'ENGINE': 'django.db.backends.postgresql',
'NAME': 'your_db',
'USER': 'your_user',
'PASSWORD': 'your_password',
'HOST': 'localhost',
'PORT': '5432',
}
}

MySQL:

DATABASES = {
'default': {
'ENGINE': 'django.db.backends.mysql',
'NAME': 'your_db',
'USER': 'your_user',
'PASSWORD': 'your_password',
'HOST': 'localhost',
'PORT': '3306',
}
}

MS SQL Server:

DATABASES = {
    'default': {
        'ENGINE': 'mssql',
        'NAME': 'your_db',
        'USER': 'your_user',
        'PASSWORD': 'your_password',
        'HOST': 'localhost',
        'PORT': '',  # Default is 1433
        'OPTIONS': {
            'driver': 'ODBC Driver 17 for SQL Server',
        },
    }
}

Oracle:

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.oracle',
        'NAME': 'your_db',
        'USER': 'your_user',
        'PASSWORD': 'your_password',
        'HOST': 'localhost',
        'PORT': '1521',
    }
}

MongoDB (djongo):

DATABASES = {
    'default': {
        'ENGINE': 'djongo',
        'NAME': 'your_db',
    }
}

Step 3: Run Migrations

python manage.py makemigrations
python manage.py migrate

Django uses ORM, so your model code is the same regardless of the backend

Benefits of Django ORM

• Write clean, readable Python code instead of SQL.
• Easier to maintain and refactor.
• Automatically handles relationships, joins, and validations.
• Database-independent, Easily adaptable to various databases
• Same code works with different databases.