# DB Change

> Use for schema/data migrations (EF Core or other). Do NOT trigger for pure app-layer changes. Focus on safe rollout and rollback.

- Skill: `askaret/db-change` (Agent Skill)
- Install (CLI): `npx skillmds@latest add askaret/db-change`
- Raw SKILL.md: https://api.skillmd.com/api/skills/askaret/db-change/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: askaret (https://skillmd.com/u/askaret)
- Updated: 2026-09-10
- Page: https://skillmd.com/skills/askaret/db-change

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Principles:
- Prefer backward-compatible migrations (expand → migrate → contract).
- Minimize locking and long transactions; design for online changes where feasible.
- Data backfills must be idempotent, resumable, and observable.

Checklist:
1) Plan
- Identify tables/columns/indexes affected
- Determine rollout strategy:
  - Expand: add nullable column / new table / additive index
  - Migrate: backfill and dual-write/read if needed
  - Contract: drop old column, enforce constraints, finalize
- Define rollback approach and what "safe to retry" means

2) Migration implementation
- Create migration (EF Core / SQL tool)
- Ensure indexes/constraints are appropriate and named consistently
- Check for default values and nullability
- Evaluate lock risk (large table rewrite, index build)

3) Data backfill (if required)
- Write an idempotent backfill job/script:
  - batches with stable ordering
  - progress logging / metrics
  - safe retry without corruption
  - can be paused/resumed
- Verify performance impact (throttling, time windows)

4) App changes
- Ensure app supports both old and new schema during rollout
- Update queries/projections to avoid breaking older deployments (if relevant)

5) Verification
- Run migration locally in a realistic dataset if possible
- Add/update tests (integration tests if repo supports them)
- Document runbook for prod (timing, expected duration, monitoring)

Finish with:
- Migration plan (expand/migrate/contract steps)
- Commands run + results
- Operational notes (runtime, monitoring, rollback)
- Risks/follow-ups