django-migration

Django Migrations are a version control system for a database schema. They represent a set of operations (written in Python) that transition the database from one state to another, keeping it synchronized with the Django Models.

When you change a Model (e.g., add a new column), the database doesn’t know about it automatically. Migrations are instructions that tell the database exactly how to alter its tables to match your new Python code.

1. Developer changes models.py.
2. Developer runs python manage.py makemigrations.
3. Django compares the models to the previous state and generates a migration file (Python script).
4. Developer runs python manage.py migrate.
5. Django translates the migration file into SQL ALTER TABLE / CREATE TABLE statements and executes them.
6. Django records that this migration was applied in the django_migrations table.

graph LR
  A[Update models.py] -->|makemigrations| B(Migration File 0002_add_field.py)
  B -->|migrate| C[(Database Schema Updated)]

Migrations are like architectural blueprints showing modifications to a building. If you want to add a room, you don’t just magically have a room. You draw up the plans (makemigrations) and then the construction crew follows the plans to build it (migrate).

• Auto-generated based on model differences.
• Can be applied forward or rolled backward.
• Tracked in a special database table to prevent applying the same migration twice.

• Built from: Django Model — migrations reflect model changes.
• Related: Django ORM — works closely with the ORM.
• Related: Django Project — managed via manage.py.
• Related: Python — migrations are just Python files.

• Deleting migration files manually can cause the database state and Django state to fall out of sync, requiring complex manual fixes.
• Adding a non-nullable field to an existing table requires providing a default value.