Alembic migrations in FastAPI - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when you run alembic upgrade head?

In a FastAPI project using Alembic, what is the effect of running the command alembic upgrade head?

A It applies all pending migrations to update the database schema to the latest version.

B It deletes all migration history but keeps the database schema unchanged.

C It rolls back the last applied migration.

D It creates a new migration file with the current database schema.

💡 Hint

Think about what 'upgrade' means in database migrations.

The command alembic upgrade head applies all migrations that have not yet been applied, bringing the database schema up to the latest version defined by the migration scripts.

📝 Syntax

intermediate

Identify the correct Alembic migration script snippet to add a new column

Which snippet correctly adds a new column email of type String(255) to the users table in an Alembic migration?

A op.add_column('users', sa.Column('email', sa.String(255), nullable=False))

B op.create_column('users', 'email', sa.String(255))

C op.add('email', sa.String(255), table='users')

D op.alter_table('users').add_column('email', sa.String(255))

💡 Hint

Look for the Alembic operation that adds a column to a table.

The correct Alembic command to add a column is op.add_column with the table name and a sa.Column object describing the new column.

🔧 Debug

advanced

Why does this Alembic migration raise an error?

Given this migration snippet, why does running it cause an error?

def upgrade():
    op.add_column('items', sa.Column('price', sa.Float))

def downgrade():
    op.drop_column('items', 'cost')

A The 'sa.Float' type is invalid in Alembic migrations.

B The upgrade is missing a nullable argument for the new column.

C The downgrade tries to drop a column named 'cost' which does not exist; it should drop 'price'.

D The migration is missing a revision ID and down_revision identifiers.

💡 Hint

Check the column names used in upgrade and downgrade functions.

The downgrade function tries to drop a column named 'cost' which was never added. The correct column to drop is 'price'. This mismatch causes an error when downgrading.

❓ state_output

advanced

What is the state of the database after this migration?

Consider this Alembic migration upgrade function:

def upgrade():
    op.create_table(
        'orders',
        sa.Column('id', sa.Integer, primary_key=True),
        sa.Column('user_id', sa.Integer, nullable=False),
        sa.Column('total', sa.Float, nullable=False)
    )

What will be the state of the database after running this migration?

A The database schema remains unchanged.

B The 'orders' table is dropped from the database.

C The migration will fail because the 'total' column type is invalid.

D A new table named 'orders' exists with columns 'id', 'user_id', and 'total'.

💡 Hint

Think about what op.create_table does.

The migration creates a new table called 'orders' with the specified columns and constraints. After running, the database will have this new table.

🧠 Conceptual

expert

Why use Alembic migrations in a FastAPI project?

Which is the best explanation for why Alembic migrations are important in a FastAPI project?

A They automatically generate API endpoints based on database tables.

B They allow you to track and apply incremental database schema changes safely over time.

C They replace the need for an ORM by managing raw SQL queries.

D They provide a graphical interface to edit database tables directly.

💡 Hint

Think about managing database changes as your app evolves.

Alembic migrations help developers keep track of database schema changes and apply them incrementally, ensuring the database matches the code expectations safely and consistently.