@Transactional spring JPA .save() not necessary?

Question

I understand that if we use annotation @Transactional. "save()" method is not necessary. Is it exact?

And for my example:

@Transactional
void methodA() {
   ...
   ObjectEntity objectEntity = objectRepository.find(); 
   methodB(objectEntity);
}

void methodB(ObjectEntity obj) {
   ...
   obj.setName("toto");
   objectRepository.save(obj);    <-- is it necessary?
}

Thanks for your help

Answer 1

It works like following:

• save() attaches the entity to the session and at the end of the transaction as long as there were no exceptions it will all be persisted to the database.

• Now if you get the object from the DB (e.g. ObjectEntity objectEntity = objectRepository.find();) then that object is already attached and you don't need to call the save() method.

• If the object, however, is detached (e.g. ObjectEntity objectEntity = new ObjectEntity();) then you must use the save() method in order to attach it to the session so that changes made to it are persisted to the DB.

Answer 2

[It is a little too late, but I hope it would be helpful to future readers]:

Within a transaction context, an update to a managed instance is reflected in the persistence storage at the commit/flush time, i.e., in your case at the end of methodB(). However, calling save() comes with a cost in scenarios like yours, as stated in Spring Boot Persistence Best Practices:

The presence or absence of save() doesn’t affect the number or type of queries, but it still has a performance penalty, because the save() method fires a MergeEvent behind the scenes, which will execute a bunch of Hibernate-specific internal operations that are useless in this case. So, in scenarios such as these, avoid the explicit call of the save() method.