Question

I managed (as you can see in older posts from me) to insert a onetomany relation through hibernate. My two entity classes look like following:

Project.java:

@Entity
public class Project {

 @Id
 @GeneratedValue(strategy = GenerationType.IDENTITY)
 private int id; 
    @OneToMany(cascade = CascadeType.ALL, mappedBy="project")
    @OrderColumn(name = "project_index")
    List<Application> applications;
....

Application.java (which is a child of project. One project can have many applications, but one application belongs to just one project)

@Entity
public class Application {

 @Id
 @GeneratedValue(strategy = GenerationType.IDENTITY)
 private int id;
    @ManyToOne
    @JoinColumn(name = "project_id")
    private Project project;
...

So far, insertion of data works well. But getting data out of my database is the problem. I tried two ways:

---

Way 1: I retrieve a Project and try to get Applications out of the list attribute. But unfortunately Application entities are in a ‘storedSnapshot’, which seems pretty wrong to me. Here is a screenshot from my debug screen:

Actually that way works! I did some mistakes somewhere else…

---

Way 2: I try to retrieve a list of all applications via sql query:

public List<Application> getApplications(int project_id) {
  Session session = HibernateUtil.getSessionFactory().getCurrentSession();
  session.beginTransaction();
  List<Application> applications = session.createQuery("from Application a where a.project_id=" + project_id + " ").list();
  return applications;
 }

..which throws strange exception -.-

org.hibernate.QueryException: could not resolve property: project_id of: de..common.entities.Application [from de..common.entities.Application a where a.project_id=1 ]

Problem with way 2 is that that I mix up SQL and HQL.

---

A little help for a hibernate beginner would be great 🙂
Cheers..

Answer 1

You should be able to access the applications by simply:

List<Application> applications = project.getApplications();

PersistentBag is implementing java.util.List so you should not care of its internals.

You will just need an open session to do that, otherwise a LazyInitializationException will be thrown.