NestJS Database Standards

Priority: P0 (CRITICAL)

Selection Strategy

See references/persistence_strategy.md for database selection matrix and scaling patterns (Connection Pooling, Sharding).

Patterns

• Repository Pattern: Isolate database logic.
• TypeORM: Inject @InjectRepository(Entity).
• Prisma: Create comprehensive PrismaService.
• Abstraction: Services should call Repositories, not raw SQL queries.

Configuration (TypeORM)

• Async Loading: Always use TypeOrmModule.forRootAsync to load secrets from ConfigService.
• Sync: Set synchronize: false in production; use migrations instead.

Migrations

• Never use synchronize: true in production.
• Generation: Whenever TypeORM entity (.entity.ts) modified, migration MUST generated using pnpm migration:generate.
• Audit: Always inspect generated migration file to ensure it matches entity changes before applying.
• Production Strategies:
• CI/CD Integration (Recommended): Run pnpm migration:run in pre-deploy or post-deploy job (e.g., GitHub Actions, GitLab CI). Ensure production environment variables correctly set.
• Manual SQL (For restricted DB access): Use typeorm migration:show to get SQL or simply copy up method's SQL into management tool (like Supabase SQL Editor). Always track manual runs in migrations metadata table.
• Zero-Downtime: Use Expand-Contract pattern (Add -> Backfill -> Drop) for destructive changes.
• Seeding: Use factories for dev data; only static dicts for prod.

Best Practices

1. Pagination: Mandatory. Use limit/offset or cursor-based pagination.
2. Indexing: Define indexes in code (decorators/schema) for frequently filtered columns (where, order by).
3. Transactions: Use QueryRunner (TypeORM) or $transaction (Prisma) for all multi-step mutations to ensure atomicity.

Anti-Patterns

• No synchronize in production: Use explicit migrations; synchronize: true drops and recreates columns.
• No raw entity returns from services: Map to DTOs before leaving service layer.
• No unpaginated list queries: All list endpoints must implement limit/offset or cursor pagination.