name: create-db-migration description: Creates Alembic database migrations safely. Use when schema changes are needed, adding tables, columns, indexes, or modifying database structure. allowed-tools: Read, Bash(docker compose exec back:*), Glob, Grep

Create Database Migration

Creates Alembic database migrations for schema changes.

Prerequisites

Ensure Docker containers are running:

docker compose ps

If not running, start them:

docker compose up -d

Workflow

1. Create Migration

docker compose exec back uv run alembic revision --autogenerate -m "Description of change"

Good migration descriptions:

• "Add notifications table"
• "Add index on users.email"
• "Add description column to items"
• "Remove deprecated legacy_id column"

2. Review Migration

After creation, review the generated migration file in back/alembic/versions/.

Check for:

• Correct upgrade() and downgrade() operations
• No data loss in downgrade()
• Proper index creation
• Foreign key constraints

3. Apply Migration Locally

Migrations run automatically on container restart, or manually:

docker compose exec back uv run alembic upgrade head

4. Verify

docker compose exec back uv run alembic current

Common Migration Patterns

Add Column

def upgrade():
    op.add_column('table_name', sa.Column('column_name', sa.String(), nullable=True))

def downgrade():
    op.drop_column('table_name', 'column_name')

Add Index

def upgrade():
    op.create_index('ix_table_column', 'table_name', ['column_name'])

def downgrade():
    op.drop_index('ix_table_column', table_name='table_name')

Add Table

def upgrade():
    op.create_table(
        'table_name',
        sa.Column('id', sa.UUID(), primary_key=True),
        sa.Column('created_at', sa.DateTime(), nullable=False),
    )

def downgrade():
    op.drop_table('table_name')

Warnings

• Destructive operations: Be careful with DROP TABLE, DROP COLUMN
• Data migrations: Consider data preservation in downgrade
• Production: Migrations run via Lambda, triggered by CI/CD after deployment

Production Migration

In deployed environments:

• Migrations run via dedicated Migration Lambda
• Triggered automatically by CI/CD after deployment
• Manual trigger: aws lambda invoke --function-name template-saas-api-migrate-lambda-{stage} /dev/null