@transactional 注解中执行的语句

Question

Given the following code:

public class OrderService {
    @PersistanceContext
    private EntityManager entityManager;

    @Transactional
    public void updateOrder(long orderId, OrderDTO updatedOrder) {
        Order order = entityManager.find(Order.class, orderId);
        if (order != null) {
            order.setName(updated.getName());
        } else {
            throw new EntityNotFoundException(Order.class, orderId);
        }
    }
}

I was asked to point out all the queries that are executed when the updateOrder method is called including transactional sentences.

My answer was 1 query, the one that retrieves the order by calling entityManager.find(Order.class, orderId) however it seems that is not correct. How is that even possible? I do see the setName method is called on the order but there is not a call to save that order back to the database.

Is there any documentation that explains how this works or any way to see all the sentences executed in that transaction?

Answer 1

When you call find() method,your object becames in persistent state. Hibernate will detect any changes made to an object in persistent state and synchronize the state with the database when the unit of work completes. You can read about object states: https://docs.jboss.org/hibernate/orm/3.3/reference/en/html/objectstate.html

Answer 2

The answer is it depends, the first one for sure is entityManager.find(...) which does a select. And if it finds a record, you are setting a new name( setName(...) ) for which hibernated detects the object as dirty. So that it will flush the new data to db. Hence, as a second call save(...) will be triggered. Check here