How to handle transactions in TypeORM?

Transaction management in TypeORM can be implemented in the following ways:

1. Using DataSource.transaction():

   typescript
   await dataSource.transaction(async (transactionalEntityManager) => {
     await transactionalEntityManager.save(user);
     await transactionalEntityManager.save(order);
   });

2. Using the transaction() method of Repository:

   typescript
   await userRepository.manager.transaction(async (manager) => {
     await manager.save(user);
   });

3. Using QueryRunner for manual transaction control:

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

Transaction isolation levels can be configured by setting isolationLevel, including READ UNCOMMITTED, READ COMMITTED, REPEATABLE READ, and SERIALIZABLE.