NestJS + TypeORM Integration Skill

Purpose

You are a specialized assistant for integrating TypeORM with NestJS in a clean, scalable, and production-friendly way.

Use this skill to:

• Set up TypeORM in a NestJS project (data source, modules, config)
• Define or refactor entities and their relations
• Configure migrations and environment-specific DB settings
• Wire repositories into services using Nest DI
• Implement transactions and query patterns safely
• Optimize DB usage (indexes, query patterns, relations loading) at a structural level

Do not use this skill for:

• General NestJS module/service/controller scaffolding → use nestjs-project-scaffold / nestjs-modules-services-controllers
• Authentication logic → use nestjs-authentication
• Supabase-specific flows → use Supabase skills (unless Supabase Postgres is accessed via TypeORM as a plain DB)

If CLAUDE.md exists, follow its rules on database choice, naming conventions, and directory layout.

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When To Apply This Skill

Trigger this skill when the user asks for things like:

• “Set up TypeORM in this NestJS API.”
• “Create entities and migrations for these tables in NestJS + TypeORM.”
• “Wire repositories into my Nest services.”
• “Fix or refactor our NestJS TypeORM config.”
• “Add relations between these entities and update the service logic.”
• “Handle transactions for this multi-step operation.”

Avoid using this skill when:

• Only high-level REST API contracts are changing without DB impact.
• Only pure in-memory logic is being implemented.

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Assumptions & Defaults

Unless the project states otherwise, assume:

• Database: Postgres (can be adapted to MySQL, SQLite, etc.)
• TypeORM version: current stable for NestJS
• Connection is configured via Nest’s TypeOrmModule
• Config is environment-driven via @nestjs/config and .env files
• Entities live in src/modules/<feature>/entities or src/entities depending on project style
• Migrations live in src/migrations or migrations directory

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High-Level Architecture

Recommended structure (adapt as needed):

project-root/
  src/
    config/
      database.config.ts
    modules/
      user/
        user.module.ts
        user.service.ts
        user.controller.ts
        entities/
          user.entity.ts
      post/
        post.module.ts
        post.service.ts
        post.controller.ts
        entities/
          post.entity.ts
    infrastructure/
      database/
        ormconfig.ts or data-source.ts (optional central place)
  migrations/
    1710000000000-CreateUserTable.ts
    1710000001000-CreatePostTable.ts

This skill should align with the existing structure rather than forcing a totally new one, unless the project is greenfield.

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Step-by-Step Workflow

When this skill is active, follow these steps:

1. Set Up TypeORM Module Configuration

If TypeORM is not configured yet:

• Install TypeORM + DB driver for the chosen database.
• Configure TypeOrmModule in AppModule or a dedicated DatabaseModule.

Example using @nestjs/config:

// src/config/database.config.ts
import { registerAs } from "@nestjs/config";

export default registerAs("database", () => ({
  type: "postgres",
  host: process.env.DB_HOST ?? "localhost",
  port: parseInt(process.env.DB_PORT ?? "5432", 10),
  username: process.env.DB_USERNAME ?? "postgres",
  password: process.env.DB_PASSWORD ?? "postgres",
  database: process.env.DB_NAME ?? "app_db",
}));

// src/app.module.ts
import { Module } from "@nestjs/common";
import { ConfigModule, ConfigService } from "@nestjs/config";
import databaseConfig from "./config/database.config";
import { TypeOrmModule } from "@nestjs/typeorm";

@Module({
  imports: [
    ConfigModule.forRoot({
      isGlobal: true,
      load: [databaseConfig],
    }),
    TypeOrmModule.forRootAsync({
      inject: [ConfigService],
      useFactory: (config: ConfigService) => {
        const db = config.get("database");
        return {
          ...db,
          autoLoadEntities: true,
          synchronize: false, // prefer migrations in production
        };
      },
    }),
    // feature modules...
  ],
})
export class AppModule {}

Key rules:

• synchronize: false in all non-dev environments (this skill encourages migrations).
• autoLoadEntities: true is acceptable for many apps; for stricter control, explicitly list entities.

2. Environment Variables

Ensure .env (and .env.example) contain:

DB_HOST=localhost
DB_PORT=5432
DB_USERNAME=postgres
DB_PASSWORD=postgres
DB_NAME=app_db

This skill should help keep secrets out of code and only in env/config.

3. Entities Design

For each feature, create entity classes:

// src/modules/user/entities/user.entity.ts
import {
  Column,
  CreateDateColumn,
  Entity,
  PrimaryGeneratedColumn,
  UpdateDateColumn,
} from "typeorm";

@Entity({ name: "users" })
export class User {
  @PrimaryGeneratedColumn("uuid")
  id!: string;

  @Column({ unique: true })
  email!: string;

  @Column()
  passwordHash!: string;

  @Column({ default: true })
  isActive!: boolean;

  @CreateDateColumn()
  createdAt!: Date;

  @UpdateDateColumn()
  updatedAt!: Date;
}

Relations example:

// src/modules/post/entities/post.entity.ts
import {
  Column,
  CreateDateColumn,
  Entity,
  ManyToOne,
  PrimaryGeneratedColumn,
} from "typeorm";
import { User } from "../../user/entities/user.entity";

@Entity({ name: "posts" })
export class Post {
  @PrimaryGeneratedColumn("uuid")
  id!: string;

  @Column()
  title!: string;

  @Column({ type: "text" })
  content!: string;

  @ManyToOne(() => User, (user) => user.posts, { onDelete: "CASCADE" })
  author!: User;

  @CreateDateColumn()
  createdAt!: Date;
}

This skill should:

• Encourage using uuid or bigint for IDs consistently (per project preference).
• Use clear relation options (onDelete, eager, lazy) thoughtfully.
• Avoid putting heavy business logic directly into entities.

4. Module & Repository Wiring

Use TypeOrmModule.forFeature to inject repositories into feature modules:

// src/modules/user/user.module.ts
import { Module } from "@nestjs/common";
import { TypeOrmModule } from "@nestjs/typeorm";
import { User } from "./entities/user.entity";
import { UserService } from "./user.service";
import { UserController } from "./user.controller";

@Module({
  imports: [TypeOrmModule.forFeature([User])],
  controllers: [UserController],
  providers: [UserService],
  exports: [UserService],
})
export class UserModule {}

In UserService, inject the repository:

// src/modules/user/user.service.ts
import { Injectable } from "@nestjs/common";
import { InjectRepository } from "@nestjs/typeorm";
import { Repository } from "typeorm";
import { User } from "./entities/user.entity";
import { CreateUserDto } from "./dto/create-user.dto";

@Injectable()
export class UserService {
  constructor(
    @InjectRepository(User)
    private readonly usersRepo: Repository<User>,
  ) {}

  create(dto: CreateUserDto) {
    const entity = this.usersRepo.create({
      email: dto.email,
      passwordHash: dto.passwordHash,
    });
    return this.usersRepo.save(entity);
  }

  findAll() {
    return this.usersRepo.find();
  }

  findOne(id: string) {
    return this.usersRepo.findOne({ where: { id } });
  }

  // etc...
}

This skill should enforce:

• Repositories are injected via DI, not instantiated manually.
• Services depend on repositories, not on the data source directly (except in advanced scenarios).

5. Migrations

Encourage using migrations instead of synchronize for schema changes.

• Create a data-source.ts file if needed for CLI migrations:

// data-source.ts (or src/infrastructure/database/data-source.ts)
import "reflect-metadata";
import { DataSource } from "typeorm";
import databaseConfig from "./src/config/database.config";
import { config as loadEnv } from "dotenv";

loadEnv();

const db = databaseConfig();

export const AppDataSource = new DataSource({
  type: "postgres",
  host: db.database.host,
  port: db.database.port,
  username: db.database.username,
  password: db.database.password,
  database: db.database.database,
  entities: ["src/**/*.entity.{ts,js}"],
  migrations: ["migrations/*.{ts,js}"],
});

• Add package.json scripts for migrations (exact form depends on project):

{
  "scripts": {
    "typeorm:run": "typeorm-ts-node-commonjs migration:run -d data-source.ts",
    "typeorm:revert": "typeorm-ts-node-commonjs migration:revert -d data-source.ts",
    "typeorm:generate": "typeorm-ts-node-commonjs migration:generate -d data-source.ts migrations/AutoMigration"
  }
}

This skill should:

• Prefer explicit migration generation (migration:generate) over schema sync.
• Keep migration files small, ordered, and committed to version control.

6. Transactions & Complex Operations

For operations that require multiple DB writes, this skill should:

• Use QueryRunner or manager.transaction where needed.

Example:

import { DataSource } from "typeorm";

@Injectable()
export class OrderService {
  constructor(private readonly dataSource: DataSource) {}

  async createOrderAndItems(dto: CreateOrderDto) {
    return this.dataSource.transaction(async (manager) => {
      const order = manager.create(Order, { /* ... */ });
      await manager.save(order);

      const items = dto.items.map((itemDto) =>
        manager.create(OrderItem, {
          order,
          // ...
        }),
      );
      await manager.save(items);

      return order;
    });
  }
}

Guidelines:

• Use transactions only where needed; avoid wrapping everything by default.
• Handle error propagation correctly; if the transaction throws, it rolls back.

7. Performance & Query Patterns

This skill should guide towards:

• Using select and projections instead of always loading entire entities.
• Avoiding N+1 queries with relation loading patterns when necessary.
• Adding indexes in migrations for frequently queried columns.
• Using pagination strategies (offset/limit or cursor-based) for large lists.

8. Refactoring Existing TypeORM Usage

When refactoring:

• Identify anti-patterns:
  • Manual connection creation (bypassing Nest DI)
  • Direct use of global getRepository instead of injected repositories
  • synchronize: true in production
• Replace with:
  • TypeOrmModule configuration
  • Injected Repository<T> or DataSource
  • Migrations for schema changes

This skill should try to minimize breaking changes while improving structure.

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Interaction with Other Skills

• nestjs-project-scaffold:
  • Provides the base Nest structure; this skill plugs DB configuration into it.
• nestjs-modules-services-controllers:
  • Uses modules/services; this skill adds entities + repositories behind those services.
• nestjs-authentication:
  • Depends on user entities and user repository; this skill provides that layer.
• TypeORM-specific skills (typeorm-schema-design, typeorm-migrations-workflow):
  • Can be used in addition for deeper DB design and migration strategies.

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Example Prompts That Should Use This Skill

• “Connect this NestJS app to Postgres via TypeORM and create User & Post entities.”
• “Refactor this hand-rolled DB code into proper TypeORM modules and services.”
• “Add migrations for these schema changes and wire them into our NestJS project.”
• “Implement a transactional operation that creates an order and its items.”
• “Fix this TypeORM config; it works locally but fails in production.”

For such prompts, rely on this skill to design and implement NestJS + TypeORM integration that is robust, maintainable, and ready for production, while delegating non-DB concerns to other skills.