Database transactions and concurrency - POJOs in Action: Developing Enterprise Applications with Lightweight Frameworks - page 465

bbb AND
bbbbb r.restaurant_id = o.restaurant_id
bbb AND l.order_id = o.order_id
ORDER BY o.order_id ASC
This statement retrieves the order information from the PLACED_ORDER , RES-
TAURANT , and PLACED_ORDER_LINE_ITEM tables. The OrderDAO stores the ver-
sion in the OrderDTO , which is returned to the sendOrders() transaction script.
The OrderDAO updates the Order using the following SQL statement:
UPDATE PLACED_ORDER
SET VERSION = VERSION + 1,
STATUS = 'SENT', MESSAGE_ID = ?, SENT_TIME = ?
WHERE ORDER_ID = ? AND VERSION = ?
This UPDATE statement changes the state of a specific order to SENT and updates
the MESSAGE_ID , SENT_TIME , and VERSION columns only if the VERSION column is
unchanged since it was read.
The markOrderAsSent() method, which executes the UPDATE statement, checks
the count of the rows updated and throws an exception if it is zero. It executes the
UPDATE statement by calling SqlMapClientTemplate.update() :
public class OrderDAOIBatisImpl extends SqlMapClientDaoSupport
implements OrderDAO {
public OrderDAOIBatisImpl(
SqlMapClientTemplate sqlMapClientTemplate) {
setSqlMapClientTemplate(sqlMapClientTemplate);
}
void markOrdersAsSent(List orders, …) {
…
int rowCount = getSqlMapClientTemplate()
.update("markOrderAsSent", …);
if (rowCount == 0)
throw new OptimisticLockingFailureException();
…
}
…
If the rowCount is zero, this method throws an OptimisticLockingFailureExcep-
tion , which is a Spring framework data access exception that is described in more
detail in section 12.2.5. In section 12.4, we describe how the application can catch
this exception and retry the transaction.