Hi,

I've become familiar with the basics of Hibernate through some various online tutorials. However, there's one concept which none of the tutorials introduce, but which often is mentioned on this forum: transactions.

What is the consequence of not using transactions, but simply performing the whole SELECT/UPDAT/DELETE process withouth commencing a transaction? For instance, a tutorial gives this example:



There isn't any transactions involved here. However, on the other side, everything i've been trying out works just fine withouth transactions.

So, my question would be: why would i use transactions and what good do they do?

http://www.google.com/search?q=hibernat ... ransaction

Well... as long as everything works you will often not notice a difference between using a transaction or not. If things start to go badly you will see a big difference. This is because a single operation may actually be made up of several SQL statements. If you use transactions it doesn't matter where in the sequence things start to go wrong, since the entire transaction is rolled back and your database is returned to the state it was in before the first SQL was executed. If you don't use transactions your database can be left in an inconsistent state since only some SQL statements was processed. A simple case is the traditional money transfer between two accounts. In it's simplest form it involves two SQL statements, one that decreases the amount in the FROM account and one that increases the amount in the TO account. Imagine what would happen if only one of the statements was successful!

This is just one case were transactions are useful. They are also needed when you have multiple clients accessing the same database at the same time. In most cases, a client doesn't want to see changes from other clients until the entire operation has completed successfully. Using transactions is a way to control that.