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alembic-migration

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Create, review, and apply database schema changes with Alembic. Use whenever a SQLAlchemy model is added or changed, a column/index/constraint needs to change, or a data backfill is required — anything that alters the PostgreSQL schema.

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Source SKILL.md: https://github.com/vstorm-co/full-stack-ai-agent-template/blob/HEAD/template/%7B%7Bcookiecutter.project_slug%7D%7D/.claude/skills/alembic-migration/SKILL.md

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Alembic Migrations

This project uses async SQLAlchemy 2.0 + Alembic on PostgreSQL. Migrations live in backend/alembic/versions/ and are numbered (0001_…, 0002_…).

Workflow

  1. Change the model first in backend/app/db/models/ (Mapped[...] + mapped_column(), __repr__, relationships with ondelete="CASCADE"). Make sure the model is imported in backend/app/db/models/__init__.py so autogenerate sees it.

  2. Autogenerate the migration:

    cd backend && uv run alembic revision --autogenerate -m "add <thing>"
# or: make db-migrate

  3. ALWAYS review the generated file. Autogenerate is a draft, not the truth:

    • Confirm upgrade() matches your intent and downgrade() actually reverses it.
    • Check the down_revision chains onto the current head (uv run alembic heads).
    • Watch for dropped columns/tables you didn't intend, server defaults, enum changes, and JSON/array types.
    • Name the revision file with the next sequential prefix to match the existing convention.

  4. Apply and verify:

    cd backend && uv run alembic upgrade head   # or: make db-upgrade
uv run alembic current                       # confirm at head

    Then round-trip once to prove downgrade() works: alembic downgrade -1 && alembic upgrade head.

Data migrations / backfills

For backfills, add explicit op.execute(...) or a small data-loop in upgrade() (see the existing *_backfill_*.py migrations for the pattern). Keep schema and data changes in separate, well-named revisions when practical.

Rules

  • Never edit a migration that has already been applied in shared environments — add a new one.
  • make dev / make bootstrap run alembic upgrade head automatically; you don't need a separate step in dev.
  • Keep models and migrations in sync — a model change without a migration will pass tests (sessions are mocked) but break on real Postgres.