Develop Reference

Delete all rows from a mysql table

I'm trying to delete all the records from a MySQL table (46 records).
The code I have tried. Any suitable answer?
Session hs = connection.NewHibernateUtil.getSessionFactory().openSession();
Criteria cr = hs.createCriteria(Bookmark.class);
Bookmark b;
List<Bookmark> li = cr.list();
for (Bookmark s : li) {
b = new Bookmark();
b.setId(s.getId());
Transaction tr = hs.beginTransaction();
hs.delete(b);
tr.commit();
hs.flush();
hs.close();
}
Error
org.hibernate.NonUniqueObjectException: a different object with the same identifier value was already associated with the session: [mypojos.Bookmark#7]

You cant delete objects like that. You would first have to get the object from db and then you can delete using hs.delete(b); this is usually used when you have to cascade changes to associated objects.
Best approach in this case is to use HQL query something like this.
String stringQuery = "DELETE FROM tablename";
Query query = session.createQuery(stringQuery);
query.executeUpdate();

How to update a JPA entity using Querydsl?

I am trying to query JPA with Querydsl (4.1.4) as written here
http://www.querydsl.com/static/querydsl/latest/reference/html/ch02.html#jpa_integration . I use Hibernate (5.2.12.Final) as the JPA backend. I generate Querydsl query types from the JPA annotated classes using the apt-maven-plugin with the com.querydsl.apt.jpa.JPAAnnotationProcessor processor.
I have an issue while updating an entity : the updated value does not show up in the Java code. Here is the relevant code snippet that updates a boolean property (named success) in the Entity :
final EntityManagerFactory entityManagerFactory = PersistenceTestUtils.buildEntityManagerFactory();
final EntityManager entityManager = entityManagerFactory.createEntityManager();
final EntityTransaction transaction = entityManager.getTransaction();
transaction.begin();
final QJpaUpdateRound qJpaUpdateRound = QJpaUpdateRound.jpaUpdateRound;
final JPQLQueryFactory queryFactory = new JPAQueryFactory(entityManager);
final QJpaUpdateRound qJpaUpdateRound = QJpaUpdateRound.jpaUpdateRound;
final JPQLQueryFactory queryFactory = new JPAQueryFactory(entityManager);
final long roundId = 3L;
System.out.println("Original " +originalRound);
queryFactory //
.update(qJpaUpdateRound) //
.set(qJpaUpdateRound._success, true) //
.where(qJpaUpdateRound._id.eq(roundId)) //
.execute();
// entityManager.clear(); // Workaround
// Fetch the updated value
final UpdateRound updatedRound = queryFactory //
.selectFrom(qJpaUpdateRound) //
.where(qJpaUpdateRound._id.eq(roundId)) //
.fetchOne();
transaction.commit();
System.out.println("Updated "+ updatedRound);
This prints :
Original JpaUpdateRound{id=3; instant=2017-11-06T19:27:01.141Z;
success=false} Updated JpaUpdateRound{id=3;
instant=2017-11-06T19:27:01.141Z; success=false}
Also, an identity test on originalRound and updatedRound shows that both variables are the same instance.
I checked in the database : the value is really updated. And if I uncomment the following line
entityManager.clear(); // Workaround
The program prints
Original JpaUpdateRound{id=3; instant=2017-11-06T19:39:01.038Z;
success=false} Updated JpaUpdateRound{id=3;
instant=2017-11-06T19:39:01.038Z; success=true}
which is the result I expect.
It seems that the entity cache does not get updated when the Querydsl update is performed. Thus, it only returns the original Java object.
Why ? How can I synchronize the JPA backend and Querydsl ?

It appears there is no other way than manually tell the entity manager that it should refresh its data. Whether using entityManager.refresh(entity) on each entity that needs to be reloaded from the database; whether by clearing the whole entity manager cache by calling entityManager.clear().
See Force refresh of collection JPA entityManager

Hibernate update with same column

SQL statement:
UPDATE table SET column = 'new_value' WHERE column = 'old_value'
(same column name)
How to do this in Hibernate?

You may use EntityManager.merge() which can lead to NonUniqueObjectException if there are multiple results are found with same column name.
Better to use NamedQuery ot NativeNamedQuery to achieve this.

My understanding is that you would want to perform batch updates.
I suggest you refer to this link
You can make use of the below code in order to get this done.
Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();
String hqlUpdate = "update Customer c set c.name = :newName where c.name = :oldName";
int updatedEntities = s.createQuery( hqlUpdate )
.setString( "newName", newName )
.setString( "oldName", oldName )
.executeUpdate();
tx.commit();
session.close();
Do note the below point mentioned in the link.
Joins, either implicit or explicit, are prohibited in a bulk HQL query. You can use sub-queries in the WHERE clause, and the sub-queries themselves can contain joins.

Hibernate simple select query doesn't return anything

I got this simple Hibernate query set up but it returns nothing, here is my code:
EntityManagerFactory emf = javax.persistence.Persistence.createEntityManagerFactory("timereg");
EntityManager em = emf.createEntityManager();
int id = em.createQuery("SELECT emp.id FROM Employee as emp WHERE emp.bsn = '398723916'").getFirstResult();
object.getEmployee().setId(id);
System.out.println("query returns employee id: " + id);
The stupid thing is that id stays zero but when i execute this query in PostgreSQL it returns 37.
I think hibernate does not like my way of implementing a select query, does anyone know what is wrong with my select query ?
THE ANSWER:
There was nothing wrong with the select query i just had to use getSingeResult() instead of getFirstResult();
Change the code into:
EntityManagerFactory emf = javax.persistence.Persistence.createEntityManagerFactory("timereg");
EntityManager em = emf.createEntityManager();
Object ob = em.createQuery("select id from Employee where bsn = '398723917'").getSingleResult();
object.getEmployee().setId(Integer.parseInt(ob.toString()));
System.out.println(ob);
This is the total solution for my problem, but i got inspired by Yanflea so he deserves all the credits.

You are using the method getFirstResult(), which gives you the position of the record in the table. You should use getSingleResult() instead. See http://docs.oracle.com/javaee/6/api/javax/persistence/Query.html.
EDIT
Here it is :
Object ob = em.createQuery("select id from Employee where bsn = '398723917'").getSingleResult();

Hibernate is not deleting my objects. Why?

I have just set up a test that checks that I am able to insert entries into my database using Hibernate. The thing that drives me crazy is that Hibernate does not actually delete the entries, although it reports that they are gone!
The test below runs successfully, but when I check my DB afterwards the entries that were inserted are still there! I even try to check it using assert (yes I have -ea as vm parameter). Does anyone have a clue why the entries are not deleted?
public class HibernateExportStatisticDaoIntegrationTest {
HibernateExportStatisticDao dao;
Transaction transaction;
#Before
public void setUp(){
assert numberOfStatisticRowsInDB() == 0;
dao = new HibernateExportStatisticDao(HibernateUtil.getSessionFactory());
}
#After
public void deleteAllEntries(){
assert numberOfStatisticRowsInDB() != 0;
Session session = HibernateUtil.getSessionFactory().getCurrentSession();
for(PersistableStatisticItem item:allStatisticItemsInDB()) {
session.delete(item);
}
session.flush();
assert numberOfStatisticRowsInDB() == 0;
}
#Test public void exportAllSavesEntriesToDatabase(){
int expectedNumberOfStatistics = 20;
dao.exportAll(StatisticItemFactory.createTestStatistics(expectedNumberOfStatistics));
assertEquals(expectedNumberOfStatistics, numberOfStatisticRowsInDB());
}
private int numberOfStatisticRowsInDB() {
return allStatisticItemsInDB().size();
}
#SuppressWarnings("unchecked")
private List<PersistableStatisticItem> allStatisticItemsInDB(){
Session session = HibernateUtil.getSessionFactory().getCurrentSession();
transaction = session.beginTransaction();
Query q = session.createQuery("FROM PersistableStatisticItem item");
return q.list();
}
}
The console is filled with
Hibernate: delete from UPTIME_STATISTICS where logDate=? and serviceId=?
but nothing has been deleted when I check it.

I guess it's related to inconsistent use of transactions (note that beginTransaction() in allStatisticItemsInDB() is called several times without corresponding commits).
Try to manage transactions in proper way, for example, like this:
Session session = HibernateUtil.getSessionFactory().getCurrentSession();
Transaction tx = session.beginTransaction();
for(PersistableStatisticItem item:
session.createQuery("FROM PersistableStatisticItem item").list()) {
session.delete(item);
}
session.flush();
assert session.createQuery("FROM PersistableStatisticItem item").list().size() == 0;
tx.commit();
See also:
13.2. Database transaction demarcation

I have the same problem. Although I was not using transaction at all. I was using namedQuery like this :
Query query = session.getNamedQuery(EmployeeNQ.DELETE_EMPLOYEES);
int rows = query.executeUpdate();
session.close();
It was returning 2 rows but the database still had all the records. Then I wrap up the above code with this :
Transaction transaction = session.beginTransaction();
Query query = session.getNamedQuery(EmployeeNQ.DELETE_EMPLOYEES);
int rows = query.executeUpdate();
transaction.commit();
session.close();
Then it started working fine. I was using SQL server. But I think if we use h2, above code (without transaction) will also work fine.
One more observation : To insert and get records usage of transaction is not mandatory but for deletion of records we will have to use transaction. (only tested in SQL server)

Can you post your DB schema and HBM or Fluent maps? One thing that got me a while back was I had a ReadOnly() in my Fluent map. It never threw an error and I too saw the "delete from blah where blahblah=..." in the logs.