The document provides an overview of Django, a high-level Python web framework, and explains the concept of schema evolution, which involves managing changes to the database schema as application requirements evolve. It details the use of Django migrations for applying these changes, including core commands like 'makemigrations' and 'migrate', types of schema changes, and best practices for managing migrations effectively. Also discussed are conflict resolution strategies, data migrations, and additional tools that enhance Django's database management capabilities.

1. Django Schema Evolution
MANAGING DATABASE SCHEMA CHANGES IN DJANGO

2. Introduction to Django
• Django Overview:
• Django is a high-level Python web framework that
encourages rapid development and clean, pragmatic
design.
• It follows the "batteries-included" philosophy, providing a
wide range of features out-of-the-box.
• Key Features:Built-in ORM for database interactions.
 Automatic admin interface.
 Robust security features.
 Scalability and flexibility.

3. What is Schema Evolution?
 Schema evolution is the process of managing and applying changes to the
database schema over time.
• Allows the database structure to evolve as application requirements change.
• Ensures that new features can be integrated without disrupting existing
functionality.

4. Why Schema Evolution is Important
• Adaptability:
• Adjust the database to meet evolving business requirements.
• Data Integrity:
• Ensure the database accurately reflects the data model and
application logic.
• Performance:
• Optimize queries and data storage.
• Compliance:
• Meet regulatory requirements by ensuring accurate data
modeling.

5. Django Migrations
•Django migrations are a powerful tool for
handling database schema changes.
•Core Commands:
•‘Makemigrations’: Generates migration files
based on changes in models.
•migrate: Applies migrations to the database.
•Migration Files:
•Contain instructions for database operations like
creating tables, adding columns, and more.

6. Creating Migrations
•Command: makemigrations
•Scans the models.py files for changes and creates migration files.
•Example: python manage.py makemigrations
•Command: migrate
•Applies the generated migrations to the database.
•Example: python manage.py migrate
•Example Workflow:
•Modify models in models.py.
•Run python manage.py makemigrations.
•Review generated migration files.
•Run python manage.py migrate to apply changes.

7. Types of Schema Changes
•Adding Fields:
•Example: models.CharField(max_length=100)
•Removing Fields:
•Example: Removing a column from a table.
•Changing Field Types:
•Example: Changing an IntegerField to a FloatField.
•Renaming Models or Fields:
•Example: Renaming username to user_name.
•Creating/Deleting Tables:
•Example: Adding a new model or deleting an obsolete
one.
•Adding Constraints and Indexes:
•Example: Adding a unique constraint or an index for

8. Managing Complex Migrations
 Dependencies:
•Migrations can depend on each other, ensuring they are applied in the
correct order.
•Example: dependencies = [('app_name', '0001_initial')]
•Data Migrations:
•Custom migrations for data transformation.
•Use RunPython or RunSQL to execute custom Python code or SQL.
•Example: migrations.RunPython(forwards_func, backwards_func)
•Reversing Migrations:
•Use the migrate command to roll back changes.
•Example: python manage.py migrate app_name 0001

9. Handling Migration Conflicts
•Conflict Scenarios:
•Multiple developers create conflicting migrations on the same
models.
•Resolution:
•Manually merge migration files.
•Ensure combined migration applies all intended changes.
•Squashing Migrations:
•Use ‘squashmigrations’ to merge multiple migrations into
one.
•Example: ‘python manage.py squashmigrations app_name
0001 0010’
•Example Workflow:
•Detect conflicts during ‘makemigrations’.

10. Best Practices
• Incremental Changes:
• Keep migrations small and manageable.
• Testing:
• Test migrations in a staging environment before applying to
production.
• Version Control:
• Use version control to track migration files and changes.
• Documentation:
• Document changes and reasoning behind migrations.
• Review:
• Regularly review and refactor migrations to keep them clean.

11. Tools and Extensions
•Django Extensions:
•Additional commands and tools for enhancing Django’s
capabilities.
•Example: django-extensions for advanced management
commands.
•South:
•Legacy migration tool used before Django 1.7.
•Third-Party Libraries:
•Tools like django-dbbackup for database backups and
restores.
•Example: python manage.py dbbackup

12. Thank You