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I'm learning about @Transactional and I want to ask you a question. Why is important to use @Transactional at the following methods?

@Repository
public class CustomerDAOImpl implements CustomerDAO {

    // need to inject the session factory
    @Autowired
    private SessionFactory sessionFactory;

    @Override
    @Transactional
    public List<Customer> getCustomers() {

        // get the current hibernate session
        Session currentSession = sessionFactory.getCurrentSession();

        // create a query  ... sort by last name
        Query<Customer> theQuery = 
                currentSession.createQuery("from Customer order by lastName",
                                            Customer.class);

        // execute query and get result list
        List<Customer> customers = theQuery.getResultList();

        // return the results       
        return customers;
    }

    @Override
    @Transactional
    public void saveCustomer(Customer theCustomer) {

        // get current hibernate session
        Session currentSession = sessionFactory.getCurrentSession();

        // save/upate the customer ... finally LOL
        currentSession.saveOrUpdate(theCustomer);

    }

    @Override
    @Transactional
    public Customer getCustomer(int theId) {

        // get the current hibernate session
        Session currentSession = sessionFactory.getCurrentSession();

        // now retrieve/read from database using the primary key
        Customer theCustomer = currentSession.get(Customer.class, theId);

        return theCustomer;
    }

    @Override
    @Transactional
    public void deleteCustomer(int theId) {

        // get the current hibernate session
        Session currentSession = sessionFactory.getCurrentSession();

        // delete object with primary key
        Query theQuery = 
                currentSession.createQuery("delete from Customer where id=:customerId");
        theQuery.setParameter("customerId", theId);

        theQuery.executeUpdate();       
    }

}

I thought that we need to use @Transactional when we have 2 or more writes on a database. For example if we want to transfer $100 from user A to user B. In this case we need to do 2 things, first we need to decrease $100 from user A, and second we need to add $100 to user B. And we need this 2 writes as a single atomic operation. And I understand why we need @Transactional in this situation.

But what I don't understand is why do we need @Transactional for the 4 methods in the above code. In getCustomers() method we just retrieve the customers, in saveCustomer() we just save a customer in the database, deleteCustomer() we just delete a customer. So in these methods we have only one write in the database. Then why do we need @Transactional? Thank you!

0 Answers0