agent-skills/skills/nestjs-best-practices/rules/db-use-migrations.md

title, impact, impactDescription, tags

title	impact	impactDescription	tags
Use Database Migrations	HIGH	Enables safe, repeatable database schema changes	database, migrations, typeorm, schema

Use Database Migrations

Never use synchronize: true in production. Use migrations for all schema changes. Migrations provide version control for your database, enable safe rollbacks, and ensure consistency across all environments.

Incorrect (using synchronize or manual SQL):

// Use synchronize in production
TypeOrmModule.forRoot({
  type: 'postgres',
  synchronize: true, // DANGEROUS in production!
  // Can drop columns, tables, or data
});

// Manual SQL in production
@Injectable()
export class DatabaseService {
  async addColumn(): Promise<void> {
    await this.dataSource.query('ALTER TABLE users ADD COLUMN age INT');
    // No version control, no rollback, inconsistent across envs
  }
}

// Modify entities without migration
@Entity()
export class User {
  @Column()
  email: string;

  @Column() // Added without migration
  newField: string; // Will crash in production if synchronize is false
}

Correct (use migrations for all schema changes):

// Configure TypeORM for migrations
// data-source.ts
export const dataSource = new DataSource({
  type: 'postgres',
  host: process.env.DB_HOST,
  port: parseInt(process.env.DB_PORT),
  username: process.env.DB_USERNAME,
  password: process.env.DB_PASSWORD,
  database: process.env.DB_NAME,
  entities: ['dist/**/*.entity.js'],
  migrations: ['dist/migrations/*.js'],
  synchronize: false, // Always false in production
  migrationsRun: true, // Run migrations on startup
});

// app.module.ts
TypeOrmModule.forRootAsync({
  inject: [ConfigService],
  useFactory: (config: ConfigService) => ({
    type: 'postgres',
    host: config.get('DB_HOST'),
    synchronize: config.get('NODE_ENV') === 'development', // Only in dev
    migrations: ['dist/migrations/*.js'],
    migrationsRun: true,
  }),
});

// migrations/1705312800000-AddUserAge.ts
import { MigrationInterface, QueryRunner } from 'typeorm';

export class AddUserAge1705312800000 implements MigrationInterface {
  name = 'AddUserAge1705312800000';

  public async up(queryRunner: QueryRunner): Promise<void> {
    // Add column with default to handle existing rows
    await queryRunner.query(`
      ALTER TABLE "users" ADD "age" integer DEFAULT 0
    `);

    // Add index for frequently queried columns
    await queryRunner.query(`
      CREATE INDEX "IDX_users_age" ON "users" ("age")
    `);
  }

  public async down(queryRunner: QueryRunner): Promise<void> {
    // Always implement down for rollback
    await queryRunner.query(`DROP INDEX "IDX_users_age"`);
    await queryRunner.query(`ALTER TABLE "users" DROP COLUMN "age"`);
  }
}

// Safe column rename (two-step)
export class RenameNameToFullName1705312900000 implements MigrationInterface {
  public async up(queryRunner: QueryRunner): Promise<void> {
    // Step 1: Add new column
    await queryRunner.query(`
      ALTER TABLE "users" ADD "full_name" varchar(255)
    `);

    // Step 2: Copy data
    await queryRunner.query(`
      UPDATE "users" SET "full_name" = "name"
    `);

    // Step 3: Add NOT NULL constraint
    await queryRunner.query(`
      ALTER TABLE "users" ALTER COLUMN "full_name" SET NOT NULL
    `);

    // Step 4: Drop old column (after verifying app works)
    await queryRunner.query(`
      ALTER TABLE "users" DROP COLUMN "name"
    `);
  }

  public async down(queryRunner: QueryRunner): Promise<void> {
    await queryRunner.query(`ALTER TABLE "users" ADD "name" varchar(255)`);
    await queryRunner.query(`UPDATE "users" SET "name" = "full_name"`);
    await queryRunner.query(`ALTER TABLE "users" DROP COLUMN "full_name"`);
  }
}

Reference: TypeORM Migrations