Nestjs Database

NestJS Database & ORM

Best-practices reference for integrating a database into NestJS through TypeORM, Prisma, or Mongoose. Covers async module configuration, repository injection, schema lifecycle (migrations vs synchronize), transactions, relation loading, projection, DTO mapping, and indexing/pagination. Examples favor TypeORM with Prisma notes where the idiom differs.

When to Apply

• Wiring TypeOrmModule/MongooseModule/PrismaModule with ConfigService
• Injecting repositories or model services into providers
• Choosing between synchronize and migrations for schema changes
• Writing multi-step writes that must be atomic (transactions)
• Loading relations efficiently (avoiding N+1 queries)
• Selecting only needed columns / not over-fetching
• Returning data from controllers without leaking ORM entities
• Indexing queried columns and paginating large result sets

Rules

• async-module-config - configure the data layer with forRootAsync + ConfigService; never hardcode credentials
• repository-pattern - inject repositories/services into providers; keep DB access out of controllers
• migrations-not-synchronize - set synchronize: false in production and manage schema with migrations
• transactions-for-multi-write - wrap multi-step writes in a transaction (QueryRunner / dataSource.transaction / prisma.$transaction)
• avoid-n-plus-one - load relations explicitly (relations/leftJoin/include); never query inside a loop
• select-needed-columns - project specific fields; avoid SELECT * and over-fetching
• separate-entities-from-dtos - map ORM entities to response DTOs; don't expose persistence models directly
• index-and-pagination - index queried columns and paginate large results with take/skip

How to Use

Read individual rule files in rules/ for the rationale plus incorrect/correct examples. Each rule is self-contained; apply the ones relevant to the change you are making. Default to TypeORM idioms; Prisma/Mongoose equivalents are noted inline where they differ.