Database migrations with Flask-Migrate - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize Flask-Migrate with the Flask app and SQLAlchemy database.

Flask

from flask_migrate import Migrate
migrate = Migrate(app, [1])

Drag options to blanks, or click blank then click option'

Amigrate

Bdb

Capp

DMigrate

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the Flask app twice instead of the database instance.

Using the wrong variable name for the database.

You need to pass the SQLAlchemy database instance db to Migrate along with the Flask app.

2fill in blank

medium

Complete the command to create a new migration script with Flask-Migrate.

Flask

flask db [1] -m "Initial migration"

Drag options to blanks, or click blank then click option'

Amigrate

Bdowngrade

Cinit

Dupgrade

Attempts:

3 left

💡 Hint

Common Mistakes

Using upgrade instead of migrate to create migration scripts.

Using init after the project is already initialized.

The migrate command generates a new migration script based on model changes.

3fill in blank

hard

Fix the error in the command to apply migrations to the database.

Flask

flask db [1]

Drag options to blanks, or click blank then click option'

Aupgrade

Bmigrate

Cinit

Drevision

Attempts:

3 left

💡 Hint

Common Mistakes

Using migrate instead of upgrade to apply changes.

Using init after migrations are already set up.

The upgrade command applies the migration scripts to update the database schema.

4fill in blank

hard

Fill both blanks to import and initialize Flask-Migrate in your app factory function.

Flask

from flask_migrate import [1]

def create_app():
    app = Flask(__name__)
    db.init_app(app)
    [2] = [1](app, db)
    return app

Drag options to blanks, or click blank then click option'

AMigrate

Bmigrate

CMigrateApp

Dmigrate_app

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase for the class import.

Using the same name for both class and instance.

You import the class Migrate and then create an instance named migrate to initialize migrations.

5fill in blank

hard

Fill all three blanks to create a migration script and apply it in one sequence.

Flask

flask db [1] -m "Add user table"
flask db [2]
flask db [3]

Drag options to blanks, or click blank then click option'

Amigrate

Bupgrade

Cdowngrade

Dinit

Attempts:

3 left

💡 Hint

Common Mistakes

Using init in the middle of migration commands.

Mixing up upgrade and downgrade order.

First, migrate creates the migration script, then upgrade applies it, and downgrade can revert it if needed.

Practice

1. What is the main purpose of Flask-Migrate in a Flask application?

easy

A. To handle user authentication and sessions

B. To create HTML templates for the Flask app

C. To manage database schema changes safely using migrations

D. To serve static files like CSS and JavaScript

Solution

1. Step 1: Understand Flask-Migrate's role

   Flask-Migrate is a tool that helps manage changes to the database structure over time.

2. Step 2: Identify the correct purpose

   It uses migrations to safely update the database schema without losing data.

3. Final Answer:

   To manage database schema changes safely using migrations -> Option C

4. Quick Check:

   Flask-Migrate = database migrations [OK]

Hint: Flask-Migrate is about database schema changes [OK]

Common Mistakes:

• Confusing Flask-Migrate with template or static file handling
• Thinking it manages user sessions
• Assuming it creates HTML or CSS files

2. Which command correctly initializes Flask-Migrate in your Flask project?

easy

A. flask db init

B. flask migrate start

C. flask db create

D. flask migrate init

Solution

1. Step 1: Recall the initialization command

   The command to set up Flask-Migrate for the first time is flask db init.

2. Step 2: Check other options

   Other commands like flask migrate start or flask db create are incorrect or do not exist.

3. Final Answer:

   flask db init -> Option A

4. Quick Check:

   Initialize Flask-Migrate = flask db init [OK]

Hint: Use 'flask db init' to start migrations [OK]

Common Mistakes:

• Using 'flask migrate init' instead of 'flask db init'
• Confusing 'start' with 'init'
• Trying commands that don't exist in Flask-Migrate

3. Given the following commands run in order:

flask db init
flask db migrate -m "Add users table"
flask db upgrade

What is the effect on the database?

medium

A. No changes happen until the app restarts

B. The database is reset and all data is lost

C. Only a migration script is created but not applied

D. The database schema is updated with the new users table

Solution

1. Step 1: Understand each command's role

   flask db init sets up migration files, flask db migrate creates a migration script, and flask db upgrade applies changes to the database.

2. Step 2: Determine the final effect

   After running all three, the database schema is updated with the new users table as described in the migration.

3. Final Answer:

   The database schema is updated with the new users table -> Option D

4. Quick Check:

   Upgrade applies migration = schema updated [OK]

Hint: Upgrade applies migration changes to DB [OK]

Common Mistakes:

• Thinking upgrade resets the database
• Believing migrate alone applies changes
• Assuming changes need app restart

4. You run flask db migrate but see no new migration script created. What is the most likely cause?

medium

A. You forgot to run flask db init first

B. No changes detected in the models since last migration

C. The database server is down

D. You need to restart the Flask app

Solution

1. Step 1: Understand what triggers migration scripts

   flask db migrate creates a script only if it detects changes in the database models.

2. Step 2: Identify the cause of no new script

   If no changes are found, no new migration script is generated, which is the most common reason.

3. Final Answer:

   No changes detected in the models since last migration -> Option B

4. Quick Check:

   No model changes = no migration script [OK]

Hint: No model changes means no migration script [OK]

Common Mistakes:

• Assuming database server status affects migration script creation
• Thinking app restart is needed for migrations
• Forgetting to initialize migrations (less common if already done)

5. You want to rename a column in your database using Flask-Migrate. Which sequence of steps is correct?

hard

A. Update the model's column name, run flask db migrate, then flask db upgrade

B. Run flask db upgrade first, then update the model, then flask db migrate

C. Delete the old column manually, update the model, then run flask db migrate

D. Update the model, restart Flask app, then run flask db upgrade

Solution

1. Step 1: Change the model to reflect the new column name

   Modify your SQLAlchemy model to rename the column as desired.

2. Step 2: Create and apply migration

   Run flask db migrate to generate the migration script, then flask db upgrade to apply it to the database.

3. Final Answer:

   Update the model's column name, run flask db migrate, then flask db upgrade -> Option A

4. Quick Check:

   Model change + migrate + upgrade = rename column [OK]

Hint: Change model first, then migrate and upgrade [OK]

Common Mistakes:

• Running upgrade before migrate
• Manually deleting columns instead of migrating
• Restarting app without migration commands