Database migration in production in Django - Mini Project: Build & Apply

Database migration in production

📖 Scenario: You are working on a Django web application that is live in production. You need to add a new field to an existing model and safely migrate the database without downtime or data loss.

🎯 Goal: Learn how to create a new field in a Django model, generate and apply migrations, and handle the migration process carefully in a production environment.

📋 What You'll Learn

Create a new field in an existing Django model

Generate a migration file using Django management commands

Apply the migration to the production database

Ensure the migration is safe and does not cause downtime

💡 Why This Matters

🌍 Real World

Adding new features or fixing bugs often requires changing the database schema in live Django applications without causing downtime or data loss.

💼 Career

Database migration skills are essential for backend developers and DevOps engineers working with Django in production environments.

1

Add a new field to the Django model

Open the models.py file in your Django app and add a new field called is_active of type models.BooleanField with default value True to the existing UserProfile model.

Django

from django.db import models

class UserProfile(models.Model):
    username = models.CharField(max_length=150)
    email = models.EmailField()
    # Add the is_active BooleanField with default True below
    # Your code here

Hint

Use is_active = models.BooleanField(default=True) inside the UserProfile class.

2

Generate the migration file

Run the Django management command python manage.py makemigrations to create a migration file for the new is_active field.

Django

from django.db import models

class UserProfile(models.Model):
    username = models.CharField(max_length=150)
    email = models.EmailField()
    is_active = models.BooleanField(default=True)

# Run the command below in your terminal
# Your code here

Hint

Use the exact command python manage.py makemigrations in your terminal to generate migration files.

3

Apply the migration to the production database

Run the Django management command python manage.py migrate to apply the new migration and update the production database schema.

Django

from django.db import models

class UserProfile(models.Model):
    username = models.CharField(max_length=150)
    email = models.EmailField()
    is_active = models.BooleanField(default=True)

# Run in terminal:
# python manage.py makemigrations

# Now apply the migration with the command below
# Your code here

Hint

Use the exact command python manage.py migrate to apply migrations to the database.

4

Ensure safe migration practices

Add a comment in your code reminding to backup the database and test migrations in a staging environment before applying to production.

Django

from django.db import models

class UserProfile(models.Model):
    username = models.CharField(max_length=150)
    email = models.EmailField()
    is_active = models.BooleanField(default=True)

# Run in terminal:
# python manage.py makemigrations
# python manage.py migrate

# Add a comment about safe migration practices below
# Your code here

Hint

Add a clear comment reminding to backup and test migrations before production deployment.

Practice

1. What is the primary purpose of running python manage.py migrate in a Django production environment?

easy

A. To create new migration files based on model changes

B. To apply database schema changes defined in migration files

C. To start the Django development server

D. To reset the database to its initial state

Solution

1. Step 1: Understand the migrate command

   The migrate command applies changes to the database schema based on migration files already created.

2. Step 2: Differentiate from makemigrations

   makemigrations creates migration files, but migrate applies them to the database.

3. Final Answer:

   To apply database schema changes defined in migration files -> Option B

4. Quick Check:

   migrate applies changes = A [OK]

Hint: migrate applies changes, makemigrations creates files [OK]

Common Mistakes:

• Confusing migrate with makemigrations
• Thinking migrate resets the database
• Believing migrate starts the server

2. Which of the following is the correct command to create new migration files after changing Django models?

easy

A. python manage.py runserver

B. python manage.py migrate

C. python manage.py makemigrations

D. python manage.py flush

Solution

1. Step 1: Identify the command for creating migrations

   makemigrations scans model changes and creates migration files.

2. Step 2: Confirm other commands' purposes

   migrate applies migrations, runserver starts server, flush clears data.

3. Final Answer:

   python manage.py makemigrations -> Option C

4. Quick Check:

   makemigrations creates files = A [OK]

Hint: makemigrations creates files, migrate applies them [OK]

Common Mistakes:

• Using migrate instead of makemigrations to create files
• Confusing runserver with migration commands
• Using flush to manage migrations

3. Given the following sequence of commands in production:

python manage.py makemigrations
python manage.py migrate

What will happen if a model field was renamed but the migration was not created before running migrate?

medium

A. No changes will be applied to the database schema

B. An error will occur because migrate requires new migration files

C. The database schema will update correctly with the renamed field

D. The old field will be deleted automatically

Solution

1. Step 1: Understand migration dependency

   migrate applies changes only if migration files exist. Without new migration files, no schema changes happen.

2. Step 2: Effect of missing migration files

   If you rename a field but skip makemigrations, the database stays unchanged after migrate.

3. Final Answer:

   No changes will be applied to the database schema -> Option A

4. Quick Check:

   migrate needs migration files = C [OK]

Hint: Always run makemigrations before migrate to apply changes [OK]

Common Mistakes:

• Assuming migrate updates schema without migration files
• Expecting automatic field deletion
• Thinking migrate throws error without new migrations

4. You ran python manage.py migrate in production but got an error about conflicting migrations. What is the best way to fix this?

medium

A. Use python manage.py migrate --merge to resolve conflicts

B. Manually edit the database tables to match models

C. Ignore the error and restart the server

D. Delete all migration files and recreate them

Solution

1. Step 1: Identify cause of migration conflicts

   Conflicts happen when multiple migration branches exist. Django offers a merge option to fix this.

2. Step 2: Use the merge option

   migrate --merge helps combine conflicting migrations safely without deleting files or manual edits.

3. Final Answer:

   Use python manage.py migrate --merge to resolve conflicts -> Option A

4. Quick Check:

   migrate --merge resolves conflicts = D [OK]

Hint: Use migrate --merge to fix conflicts safely [OK]

Common Mistakes:

• Deleting migration files causing data loss
• Manually editing tables risking corruption
• Ignoring errors leads to bigger issues

5. In a production environment, you want to add a new non-nullable field to a large existing table without downtime. Which approach is safest?

hard

A. Add the field as non-nullable directly and run migrate

B. Skip migrations and add the field manually in the database

C. Drop the table and recreate it with the new field

D. Add the field with null=True, migrate, then update data and alter to null=False

Solution

1. Step 1: Understand downtime risks

   Adding a non-nullable field directly can lock the table and cause downtime in production.

2. Step 2: Use a two-step migration

   First add the field as nullable (null=True), migrate, then fill data, and finally alter to non-nullable (null=False).

3. Final Answer:

   Add the field with null=True, migrate, then update data and alter to null=False -> Option D

4. Quick Check:

   Two-step migration avoids downtime = B [OK]

Hint: Add nullable field first, then make non-nullable after data update [OK]

Common Mistakes:

• Adding non-nullable field directly causing downtime
• Dropping tables losing data
• Skipping migrations causing inconsistencies