Hibernate, what will happen if beginTransaction won't be used?

Question

I'm using hibernate 5.2 for connection to SQLite library. I created a new Session and used session.createNativeQuery("My sql").executeUpdate() after what I closed my Session. Everything works fine, but I came across several examples where after creating Session they begin Transaction, perform SQL operations, commit Transaction, and close Session. But not all examples online have Transaction in them and my code works fine without it.

This made me curious:

Why we need to use Transaction?
What will happen if we won't?
And most important, in which cases it needs to be used and in which not?

I use <property name="hibernate.connection.pool_size">1</property>

That has nothing todo with Java or hibernate. Transaction is a db thing — Jens, Jun 29 '17 at 10:33

score 1 · Answer 1 · answered Jun 29 '17 at 11:16

1

Why we need to use Transaction? -> What you are doing is just a simple update, transaction mgmt is used in case there are multiple updates and you want ACID nature for your transaction.

What will happen if we won't? -> If there are multiple update statements and one of them throws an exception you will have inconsistent data.

answered Jun 29 '17 at 11:16

Dhananjay

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I was executing several `SQL` queries without `Transaction` and it went fine. Can you tell a bit more about case it can go wrong? – Alyona Jun 29 '17 at 12:09
Alyona there are concepts like conflict serializable, dhanajay is referring to those – Anshuman Jayaprakash Jun 30 '21 at 16:52

score 0 · Accepted Answer · answered Jun 30 '17 at 04:38

You can try relating hibernate with JDBC and you will be getting some hints about transaction.

In JDBC you need to just open a connection start your work, and in the end you can commit or rollback.

But what if you have many different parallel tasks , which may be dependent or independent to each other. Then you may require commit/rollback each task separately or rollback if any fails.

for example
Big Task :
    small task1
    small task2
    small task3 and many more

rollback the big task if any small task fails.This can be one of the many business requirements.

In JDBC, Connection interface has provided commit() and rollback() methods.

In jpa/hibernate, Transaction interface has provided commit() and rollback() methods.

So one session can have many dependent or independent transactions.

Below is documentation from org.hibernate.Transaction

Allows the application to define units of work, while maintaining 
abstraction from the underlying transaction implementation (eg. JTA, JDBC). 

A transaction is associated with a Session and is usually 
initiated by a call to org.hibernate.Session.beginTransaction(). 
A single session might span multiple transactions since the notion of a session 
(a conversation between the application and the datastore) is of coarser granularity 
than the notion of a transaction. However, it is intended that there be at most 
one uncommitted transaction associated with a particular Session at any time.

This also might help you What is the difference between a session and a transaction in JPA 2.0?

score 0 · Answer 3 · answered Jun 30 '17 at 05:52

Let's define what is transaction - basically it is atomic unit of work.

There are two types of transaction management or transaction demarcation(think of demarcation as of starting transaction, committing or rolling transaction back) : CMT (container managed transactions) - managed by underlying container for you (JTA) and BMT(bean managed transactions) - transaction demarcation is managed programmatically by developer itself. So if you see in any example that transaction is obtained and programmatically committed or rolled back - that is example of BMT, that is when it is your responsibility of a developer to manage transaction.

Whenever you do not see explicit transaction demarcation - that means that is is CMT. This is very broad subject - I advise you to read more.

Hibernate, what will happen if beginTransaction won't be used?

3 Answers3