drizzle-safe-migrations

Development

Production-safe Drizzle migration workflow for schema changes that require data backfills or constraint tightening. Use when changing enums/check constraints/defaults, removing status values, or sequencing custom and generated migrations in Drizzle. Trigger on requests about Drizzle migration safety, deployment-safe backfills, migration ordering, and rollback planning. Don't use for ORMs other than Drizzle, app-layer query optimization, or greenfield schema design.

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Source SKILL.md: https://github.com/pedronauck/skills/blob/HEAD/skills/mine/drizzle-safe-migrations/SKILL.md

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Drizzle Safe Migrations

Overview

Use this skill to run database migrations in a way that is auditable, deployment-safe, and consistent with Drizzle's migration model.

Core Rules

Always generate schema migrations with the project script (bun run db:generate).
Never hand-edit generated schema migration files.
Generate data backfills as custom migrations (bun run db:generate -- --custom --name <name>) and edit only that custom SQL file.
Apply data normalization before tightening constraints.
Keep one-off data fixes in migration history, not as hidden runtime logic, unless an emergency hotfix requires temporary mitigation.

Workflow

Classify the change:
- schema-only: only column/table/index/default changes.
- data+schema: old rows must be transformed before new constraints/defaults.
For data+schema, create custom migration first:
- bun run db:generate -- --custom --name <descriptive_name>
- Add idempotent backfill SQL.
Generate schema migration second:
- bun run db:generate
Verify migration ordering in drizzle/meta/_journal.json:
- backfill migration index must be lower than constraint-tightening migration index.
Verify generated SQL and snapshots:
- backfill migration contains only intended data change.
- schema migration contains constraint/default/type changes.
Run full backend verification:
- bun run lint && bun run typecheck && bun run test
Document deployment notes:
- expected data transformations,
- lock-risk areas,
- rollback strategy.

Backfill Requirements

Use restrictive WHERE clauses.
Prefer idempotent updates (UPDATE ... WHERE status = 'legacy_value').
Do not mix unrelated DDL/DML in the same migration.
Keep SQL explicit and minimal.

Constraint Tightening Pattern

When removing allowed values (enum/check):

Backfill existing rows to valid target value.
Update default to new value.
Tighten check/enum constraint.

For large tables or strict uptime targets, use staged PostgreSQL patterns (NOT VALID + VALIDATE CONSTRAINT) where applicable.

Anti-Patterns

Hand-editing generated schema migration files.
Tightening constraints before backfilling existing data.
Hiding one-time migration logic in app startup code without migration artifacts.
Running migrations without validating order in the Drizzle journal.

Reference

See references/production-playbook.md for command templates and review checklists.