database-migration（数据库迁移）

You help create and manage database migrations using Alembic for the QA Team Portal backend.

When to Use This Skill

• Creating new database tables (new SQLAlchemy models)
• Adding/removing/modifying columns in existing tables
• Adding indexes or constraints
• Data migrations (transforming existing data)
• Reviewing migration files before applying

Prerequisites

• SQLAlchemy models exist in backend/app/models/
• Models are imported in backend/app/db/base.py
• Alembic is initialized (backend/alembic/ directory exists)
• Database connection configured in .env

Workflow

1. Create Migration

cd backend

# Auto-generate migration from model changes
uv run alembic revision --autogenerate -m "descriptive message"

# Or create empty migration for data changes
uv run alembic revision -m "migrate existing data"

2. Review Generated Migration

• Open the new file in backend/alembic/versions/
• Check upgrade() function for forward migration
• Check downgrade() function for rollback
• Verify changes match your intent
• Add any custom logic if needed (e.g., data transformation)

3. Apply Migration

# Apply to database
uv run alembic upgrade head

# Or apply one version
uv run alembic upgrade +1

4. Verify Migration

# Check current version
uv run alembic current

# View migration history
uv run alembic history --verbose

Common Migration Patterns

Adding a New Table

def upgrade():
    op.create_table(
        'research',
        sa.Column('id', postgresql.UUID(), nullable=False),
        sa.Column('title', sa.String(length=255), nullable=False),
        sa.Column('description', sa.Text(), nullable=True),
        sa.Column('status', sa.Enum('ongoing', 'completed', 'planned'), nullable=False),
        sa.Column('created_at', sa.DateTime(), nullable=False),
        sa.Column('updated_at', sa.DateTime(), nullable=False),
        sa.PrimaryKeyConstraint('id')
    )
    op.create_index('ix_research_status', 'research', ['status'])

def downgrade():
    op.drop_index('ix_research_status', table_name='research')
    op.drop_table('research')

Adding a Column

def upgrade():
    op.add_column('team_members',
        sa.Column('linkedin_url', sa.String(length=255), nullable=True)
    )

def downgrade():
    op.drop_column('team_members', 'linkedin_url')

Data Migration

def upgrade():
    # Add column
    op.add_column('users', sa.Column('role', sa.String(50), nullable=True))

    # Migrate data
    connection = op.get_bind()
    connection.execute(
        "UPDATE users SET role = 'member' WHERE role IS NULL"
    )

    # Make not nullable
    op.alter_column('users', 'role', nullable=False)

def downgrade():
    op.drop_column('users', 'role')

Rollback Migrations

# Rollback one version
uv run alembic downgrade -1

# Rollback to specific version
uv run alembic downgrade <revision_id>

# Rollback all migrations
uv run alembic downgrade base

Troubleshooting

"Target database is not up to date"

# Check current version
uv run alembic current

# Stamp database with current code version
uv run alembic stamp head

Migration conflicts

# List all heads
uv run alembic heads

# Merge conflicting branches
uv run alembic merge -m "merge branches" <rev1> <rev2>

Reset migrations (development only!)

# Drop all tables
uv run alembic downgrade base

# Or drop database and recreate
dropdb qa_portal
createdb qa_portal
uv run alembic upgrade head

Best Practices

1. Always review auto-generated migrations - Alembic may miss some changes
2. Test migrations on dev database first - Don't apply directly to production
3. Write reversible migrations - Ensure downgrade() actually works
4. One logical change per migration - Keep migrations focused
5. Include data migrations when needed - Don't just change schema
6. Backup production database before applying migrations
7. Use descriptive messages - Clear commit-style messages

Safety Checks

Before applying to production:

• Migration reviewed and tested on dev database
• Downgrade tested and works
• No data loss in migration
• Indexes added for new query patterns
• Foreign key constraints properly defined
• Backup of production database taken
• Deployment plan includes rollback procedure

Output Format

After creating/applying migration, report:

1. Migration file created: <filename>
2. Changes summary: What tables/columns affected
3. Applied successfully: Yes/No
4. Current database version: <revision_id>
5. Any warnings or issues encountered