Migrations concept and workflow in Django - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a migration in Django?

A migration is a way Django tracks changes to your database schema. It helps update the database structure safely as your models change.

beginner

What command do you use to create new migrations after changing models?

You use python manage.py makemigrations to create migration files that describe the changes in your models.

beginner

What does the python manage.py migrate command do?

It applies the migration files to the database, updating the database schema to match your current models.

intermediate

Why should you always review migration files before applying them?

Because migrations change your database, reviewing helps avoid mistakes like deleting data or wrong schema changes.

beginner

What is the typical workflow when you change a Django model?

1. Change your model code.
2. Run python manage.py makemigrations to create migration files.
3. Review migration files.
4. Run python manage.py migrate to update the database.
5. Test your app to ensure it works.

Which command creates migration files after model changes?

A python manage.py makemigrations

B python manage.py migrate

C python manage.py runserver

D python manage.py collectstatic

The makemigrations command creates migration files describing model changes.

What does the migrate command do?

A Creates new migration files

B Updates the database schema based on migration files

C Starts the Django development server

D Deletes old migration files

The migrate command applies migrations to update the database schema.

Why is it important to review migration files before applying them?

A To automatically fix errors in models

B To speed up the migration process

C To avoid accidental data loss or wrong schema changes

D To generate documentation

Reviewing helps catch mistakes that could harm your database.

What happens if you change a model but forget to run makemigrations?

A The migration files will be deleted

B The server will crash immediately

C Django will auto-update the database

D The database won't update to match the model changes

Without migration files, the database stays the same and can cause errors.

Which file type stores the instructions for database changes in Django migrations?

A Python files (.py)

B JSON files (.json)

C SQL files (.sql)

D Text files (.txt)

Migration files are Python scripts that describe database changes.

Explain the step-by-step workflow of making and applying migrations in Django.

Think about what happens after you change your models.

Why are migrations important in Django projects? Describe their role and benefits.

Consider how migrations help manage database changes over time.

Practice

1. What is the main purpose of Django migrations?

easy

A. To keep the database schema synchronized with Django models

B. To create HTML templates automatically

C. To manage user authentication

D. To optimize Django views for speed

Solution

1. Step 1: Understand what migrations do

   Django migrations track changes in models and update the database schema accordingly.

2. Step 2: Compare options with this purpose

   Only To keep the database schema synchronized with Django models describes keeping the database schema in sync with models, which is the core purpose of migrations.

3. Final Answer:

   To keep the database schema synchronized with Django models -> Option A

4. Quick Check:

   Migrations purpose = sync DB schema [OK]

Hint: Migrations sync models and database structure [OK]

Common Mistakes:

• Confusing migrations with template or view management
• Thinking migrations handle user authentication
• Assuming migrations optimize performance

2. Which command do you run to create new migration files after changing models?

easy

A. python manage.py migrate

B. python manage.py makemigrations

C. python manage.py runserver

D. python manage.py collectstatic

Solution

1. Step 1: Identify the command for creating migration files

   The command makemigrations generates migration files based on model changes.

2. Step 2: Differentiate from other commands

   migrate applies migrations, runserver starts the server, and collectstatic collects static files.

3. Final Answer:

   python manage.py makemigrations -> Option B

4. Quick Check:

   Create migrations = makemigrations [OK]

Hint: Use makemigrations to create migration files [OK]

Common Mistakes:

• Using migrate instead of makemigrations to create files
• Confusing runserver with migration commands
• Thinking collectstatic manages migrations

3. Given this sequence of commands:

python manage.py makemigrations
python manage.py migrate

What happens after running these commands?

medium

A. The server starts running with updated models

B. Static files are collected and served

C. Migration files are created and then applied to update the database schema

D. The database is reset to initial state

Solution

1. Step 1: Understand makemigrations effect

   This command creates migration files reflecting model changes but does not apply them yet.

2. Step 2: Understand migrate effect

   This command applies the created migration files to update the database schema accordingly.

3. Final Answer:

   Migration files are created and then applied to update the database schema -> Option C

4. Quick Check:

   makemigrations + migrate = create & apply migrations [OK]

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

Common Mistakes:

• Thinking migrate creates migration files
• Assuming these commands start the server
• Confusing static file commands with migrations

4. You ran python manage.py migrate but got an error saying a migration file is missing. What is the likely cause?

medium

A. You forgot to run makemigrations to create migration files

B. You ran migrate before starting the server

C. Your models.py file is empty

D. You need to delete the database before migrating

Solution

1. Step 1: Analyze the error about missing migration files

   This usually means migration files were not created yet for model changes.

2. Step 2: Identify the missing step

   Running makemigrations generates migration files needed before applying them with migrate.

3. Final Answer:

   You forgot to run makemigrations to create migration files -> Option A

4. Quick Check:

   Missing migration files = forgot makemigrations [OK]

Hint: Always run makemigrations before migrate [OK]

Common Mistakes:

• Thinking migrate creates migration files
• Assuming server must run before migrate
• Believing database must be deleted before migrating

5. You added a new field to a model and want to share the changes with your team. What is the correct workflow to update the database and share the changes safely?

hard

A. Delete the database, then run makemigrations and migrate on each machine

B. Run migrate first, then create migration files manually and share them

C. Only update the models.py file and ask team members to restart their servers

D. Run makemigrations, commit migration files to version control, then run migrate on all machines

Solution

1. Step 1: Create migration files after model changes

   Run makemigrations to generate migration files reflecting the new field.

2. Step 2: Share migration files and apply them

   Commit migration files to version control so the team can get them, then run migrate on each machine to update the database schema safely.

3. Final Answer:

   Run makemigrations, commit migration files to version control, then run migrate on all machines -> Option D

4. Quick Check:

   makemigrations + commit + migrate = safe team update [OK]

Hint: Commit migration files before migrating on other machines [OK]

Common Mistakes:

• Running migrate before creating migration files
• Deleting databases unnecessarily
• Only updating models.py without migrations