Operations done in one transaction are only committed at the end of the transaction. If an error occurs in the ORM, the transaction is rolled back. If you have made an INSERT or UPDATE query and you want to make it permanent, you can use self._cr.commit() to commit the changes.
Note that using commit() can be dangerous because it can put records in an inconsistent state. An error in the ORM can cause incomplete rollbacks, so only use commit() if you are completely sure.