260223:1415 20260223 nextJS & nestJS Best pratices

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

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+---
+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)