JPA - When to use getTransaction() when persisting objects

Question

I\'ve recently started working with JPA on the Google App Engine. In reading some examples, I\'ve noticed a couple of variations in the way objects are persisted. In one cas

Answer 1

Google App Engine has its transaction management (https://developers.google.com/appengine/docs/java/datastore/transactions) but the JPA transaction interface isn't aware of some of the GAE underlying functionalities (i.e. entity groups).

So it’s up to your application to decide which operations to perform in a transaction and which not. You should put in a transaction operations that have to be executed atomically.

Remember as a best practice to perform cascading actions and relationship operations in a transaction because JPA might trigger many queries and it could lead to an inconsistent data situation.

Example of using transaction with JPA2:

import javax.persistence.EntityTransaction;


EntityTransaction txn = em.getTransaction();
txn.begin();
try {
    //do something with your database
    txn.commit();
} 
finally {
   if (txn.isActive())
      txn.rollback(); 
}