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

---
title: Use Database Migrations
impact: HIGH
impactDescription: Enables safe, repeatable database schema changes
tags: 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):**

```typescript
// 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):**

```typescript
// 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](https://typeorm.io/migrations)