NestJS Database Standards

Priority: P0 (FOUNDATIONAL)

Database integration patterns and ORM standards for NestJS applications.

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 a 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 a TypeORM entity (.entity.ts) is modified, a migration MUST be generated using pnpm migration:generate.
• Audit: Always inspect the generated migration file to ensure it matches the entity changes before applying.
• Production Strategies:
  • CI/CD Integration (Recommended): Run pnpm migration:run in a pre-deploy or post-deploy job (e.g., GitHub Actions, GitLab CI). Ensure the production environment variables are correctly set.
  • Manual SQL (For restricted DB access): Use typeorm migration:show to get the SQL or simply copy the up method's SQL into a management tool (like Supabase SQL Editor). Always track manual runs in the 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 the service layer.
• No unpaginated list queries: All list endpoints must implement limit/offset or cursor pagination.