LogicDAO dao = new LogicDAO();
Logic logic=new Logic();
try {
Session s=dao.getSession();
Transaction t=s.beginTransaction();
t.begin();
logic.setUsername("aa");
logic.setPwd("aa");
dao.save(logic);
t.commit();

} catch (HibernateException e) {
System.err.println("Entity retrieval failed.");
e.printStackTrace();
} finally {
try {
dao.getSession().close();
} catch (Exception e) {
e.printStackTrace();
}
}

Error is:

Entity retrieval failed.
org.hibernate.id.IdentifierGenerationException: ids for this class must be manually assigned before calling save(): com.hibernate.db.Logic
at org.hibernate.id.Assigned.generate(Assigned.java:33)
at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:91)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:186)
at org.hibernate.event.def.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:33)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:175)
at org.hibernate.event.def.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:27)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:70)
at org.hibernate.impl.SessionImpl.fireSave(SessionImpl.java:530)
at org.hibernate.impl.SessionImpl.save(SessionImpl.java:518)
at org.hibernate.impl.SessionImpl.save(SessionImpl.java:514)
at com.hibernate.db.LogicDAO.save(LogicDAO.java:27)
at com.hibernate.db.A.main(A.java:22)

You will need to provide more information, but the first line seems to give the pointer

ids for this class must be manually assigned before calling save()


how have you set up the identity