hibernate: how to select all rows in a table

Question

I try to do something like Select * from LogEntry with Hibernate. insert works fine:

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;

[...]
protected EntityManager manager;

protected final String tableName = "LogEntry";

public DatabaseImpl(DB_TYPE db) {
    this.db = db;
    if (entityManagerFactory != null && entityManagerFactory.isOpen()) {
        entityManagerFactory.close();
    }
    entityManagerFactory = Persistence.createEntityManagerFactory(db.getPersUnit());
    manager = entityManagerFactory.createEntityManager();
}
public void insert(LogEntry entry) {

    manager.getTransaction().begin();
    manager.persist(entry);
    manager.getTransaction().commit();
}

But when I try to get the inserted values using this method: public LogEntryList getAll() {

    manager.getTransaction().begin();

    Query query = manager.createNativeQuery("SELECT * FROM " + tableName + ";");
    ArrayList<LogEntry> entries = (ArrayList<LogEntry>) query.getResultList();
    manager.getTransaction().commit();

    return new LogEntryList(entries);
}

I always get the Exception: java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to de.motza.entities.LogEntry

I know the problem is the casting of the Query result to the object, but I can't find anywhere how to cast the objects properly, or how to get more than one row from the table.

does anybody have any advice? If requested, I can post my persistence.xml and more code

Answer 1

Becuase you have used nativeQuery so you need to transfer result by using setResultTransormer method.

Query query = manager.createNativeQuery("SELECT * FROM " + tableName + ";");
query.setResultTransformer(Transformers.aliasToBean(LogEntry.class))
ArrayList<LogEntry> entries = (ArrayList<LogEntry>) query.getResultList();

Answer 2

For starters, you should try to take advantage of HQL, Hibernate Query Language. In the example you gave above, you are trying to execute a native SQL query. The reason you are getting the ClassCastException is that the native query is circumventing the framework and returning raw Objects instead of the type you want.

Try using this code instead for your SELECT *:

String hql = "from LogEntry";
Session session = entityManagerFactory.openSession();
Query query = session.createQuery(hql);
List<LogEntry> logEntries = query.list();      // no ClassCastException here