Database migration in deployment in Flask - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Flask-Migrate's role in deployment

What is the primary purpose of Flask-Migrate during the deployment of a Flask application?

A To automatically update the database schema to match the current models without losing data

B To create a backup of the database before deployment

C To optimize SQL queries for faster performance

D To generate HTML forms for database models

💡 Hint

Think about how your database structure changes when you update your code models.

Flask-Migrate helps manage database schema changes by generating migration scripts and applying them, ensuring the database matches the current models without data loss.

❓ component_behavior

intermediate

Behavior of migration commands in Flask

What happens when you run flask db migrate followed by flask db upgrade during deployment?

A <code>flask db migrate</code> applies migrations; <code>flask db upgrade</code> rolls back changes

B <code>flask db migrate</code> generates migration scripts; <code>flask db upgrade</code> applies them to the database

C <code>flask db migrate</code> deletes old migrations; <code>flask db upgrade</code> creates new tables

D <code>flask db migrate</code> backs up the database; <code>flask db upgrade</code> restores it

💡 Hint

One command prepares changes, the other applies them.

flask db migrate creates migration scripts based on model changes. flask db upgrade applies those scripts to update the database schema.

🔧 Debug

advanced

Fixing migration script conflicts

You deployed a Flask app and ran migrations. Later, a teammate also created migrations on their branch. When merging, you get a conflict in migration scripts. What is the best way to resolve this?

A Ignore the conflict and run <code>flask db upgrade</code> anyway

B Delete all migration files and recreate them from scratch

C Manually merge the conflicting migration files and then run <code>flask db upgrade</code>

D Revert the database to the previous state and avoid merging branches

💡 Hint

Migration files are code and can be merged carefully.

Conflicts in migration scripts should be resolved by merging the files carefully to keep all schema changes, then applying the migrations.

❓ state_output

advanced

Database state after partial migration

After running flask db migrate and partially applying flask db upgrade, the deployment crashes. What is the likely state of the database?

A The database schema is partially updated, causing inconsistencies and errors

B The database schema is fully updated and consistent

C The database schema remains unchanged from before migration

D The database is completely reset to an empty state

💡 Hint

Think about what happens if migration scripts are interrupted.

If the upgrade is interrupted, the database schema may be partially changed, leading to errors due to inconsistent structure.

📝 Syntax

expert

Correct Alembic migration script snippet

Which option shows the correct way to add a new column age of type Integer to the users table in an Alembic migration script?

A op.add_column('users', Column('age', Integer))

B op.add_column('users', sa.Column('age', sa.Int(), nullable=True))

C add_column('users', sa.Column('age', Integer, nullable=False))

D op.add_column('users', sa.Column('age', sa.Integer(), nullable=True))

💡 Hint

Remember to use the correct Alembic and SQLAlchemy syntax with proper imports.

The correct syntax uses op.add_column with sa.Column and sa.Integer(). Option D matches this exactly.