Transactions & Advanced

Preview — 3 of 10 questions

When using a QueryRunner directly to manage a transaction, which sequence is correct?

javascript

const queryRunner = dataSource.createQueryRunner();
await queryRunner.connect();
await queryRunner.startTransaction();
try {
  await queryRunner.manager.save(from);
  await queryRunner.manager.save(to);
  await queryRunner.commitTransaction();
} catch (err) {
  await queryRunner.rollbackTransaction();
  throw err;
} finally {
  await queryRunner.release();
}

Aconnect() → work → commitTransaction(); no rollback needed

BstartTransaction() → connect() → work → release() → commitTransaction()

CstartTransaction() → work → release(); commit is automatic

Dconnect() → startTransaction() → work → commitTransaction()/rollbackTransaction() → release()

Why is the standalone @Transaction()/@TransactionManager() decorator approach discouraged in modern NestJS/TypeORM code?

javascript

// Preferred: explicit transactional EntityManager
await dataSource.transaction(async (manager) => {
  await manager.save(orderEntity);
  await manager.decrement(Stock, { id: stockId }, 'quantity', 1);
});

AIt was deprecated/removed in favour of explicit dataSource.transaction() or QueryRunner, partly because decorator-injected managers don't integrate cleanly with NestJS DI and request scope

BIt cannot roll back

CIt only works with MySQL

DIt double-commits

Why use TypeOrmModule.forRootAsync() with ConfigService instead of forRoot() with a literal object?

javascript

TypeOrmModule.forRootAsync({
  inject: [ConfigService],
  useFactory: (config: ConfigService) => ({
    type: 'postgres',
    url: config.getOrThrow<string>('DATABASE_URL'),
    entities: [__dirname + '/**/*.entity{.ts,.js}'],
    synchronize: false,
  }),
});

AIt is the only way to set synchronize

BIt allows connection options to be built from injected, validated configuration (e.g. env vars) resolved at runtime

CIt opens connections lazily on first query

DIt is required for PostgreSQL

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