How to fetch associated entities with Hibernate

Question

I am developing an application using Spring rest and Hibernate and I want to get nested records from database like I'm getting Profession for a User, now I want to fetch Users associated to the Profession I fetched previously.

Here is my Dao class

@SuppressWarnings({ "unchecked", "rawtypes" })
public List<Profession> getProfessionById(long id) throws Exception {
    session = sessionFactory.openSession();
    Criteria cr = session.createCriteria(Profession.class);
    cr.add(Restrictions.eq("uid", id));
    List results = cr.list();
    tx = session.getTransaction();
    session.beginTransaction();
    tx.commit();
    return results;
}

Answer 1

According to you query, the Profession table has a uid column which is probably a FK to the Users table and I think the Users table should have a FK to the Profession instead.

So the Users table will have a many-to-one association to a Profession:

@ManyToOne
private Profession profession;

and the Profession can associate all Users having that particular profession, so in the Profession entity you have the inverse side of this association:

@OneToMany(mappedBy = "profession")
private List<Users> users = new ArrayList<>();

Now to get all users having a profession you can run a simple query like this:

List<Users> users = (ist<Users>) session.createQuery(
    "select u " +
    "from Profession p " +
    "join fetch p.users u " +
    "where p.id = :id")
.setParameter("id", proffesionId)
.list();

Answer 2

First you need to add below mapping in Profession and User entity class

In Profession class

//bi-directional many-to-one association to Users
@OneToMany(mappedBy="profession", cascade=CascadeType.ALL)
private List<User> users;

public List<User> getUsers() {
    return this.users;
}

public void setUsers(List<User> users) {
    this.users = users;
}

In User entity class

@ManyToOne(fetch=FetchType.EAGER)
@JoinColumn(name="profession_id")
private Profession profession;

Then you can fetch profession object by id using your existing DAO class code.

@SuppressWarnings({ "unchecked", "rawtypes" })
public List<Profession> getProfessionById(long id) throws Exception {
    session = sessionFactory.openSession();
    Profession profession =  (Profession) session.get(Profession.class, id);

    // here you can get list of users for this profession 
    // List<User> users = profession.getUsers();
    return profession;
}