What you do is called a projection. That’s when you return only a scalar value that belongs to one entity. You can do this with JPA. See scalar value. I think in this case, omitting the entity type altogether is possible: Query query = em.createNativeQuery( “select id from users where username = ?”); query.setParameter(1, “lt”); … Read more
The terms “jta-datasource” and “resouce-local datasource” are a little vague to me. I guess you actually refer to the jta-datasource and non-jta-datasource elements. In short: if the transaction type of the persistence unit is JTA, the jta-datasource element is used to declare the JNDI name of the JTA data source that will be used to … Read more
Depending on whether the transaction encloses the loop, batching typically already happens in your case. JPA will collect all your updates in its L1 cache, and typically write that all to the DB in a batch when the transaction commits. This is not really that different with batching in JDBC, where every batch-item you add … Read more
As of EJB 3.1, singleton beans can be notified of module start and stop: @Singleton @Startup public class StartupBean { @PostConstruct private void postConstruct() { /* … */ } @PreDestroy private void preDestroy() { /* … */ } } Prior to EJB 3.1, there is no standard, EJB-only solution. I’d suggest adding a WAR to … Read more
DAO is an abstraction of data persistence. Repository is an abstraction of a collection of objects. DAO would be considered closer to the database, often table-centric. Repository would be considered closer to the Domain, dealing only in Aggregate Roots. Repository could be implemented using DAO‘s, but you wouldn’t do the opposite. Also, a Repository is … Read more
Although you are getting valid results, the SQL query fetches all data and it’s not as efficient as it should. So, you have two options. Fixing the issue with two SQL queries that can fetch entities in read-write mode The easiest way to fix this issue is to execute two queries: . The first query … Read more
Fixed it by removing CascadeType.MERGE on Permission entity
The error occurs because the object’s ID is set. Hibernate distinguishes between transient and detached objects and persist works only with transient objects. If persist concludes the object is detached (which it will because the ID is set), it will return the “detached object passed to persist” error. You can find more details here and … Read more
Stateful session beans (SFSB) are not exactly what you think they are. You seem to think that they behave somehow like session scoped JSF managed beans. This is untrue. The term “session” in EJBs has an entirely different meaning than the HTTP session which you’ve had in mind. The “session” in EJBs must be interpreted … Read more