Hibernate Join between 2 tables with foreign key

Question

Im trying to get a list with results from join with two tables, but always get error. What i want is List with person and job name

• Error

  • Cannot invoke "org.hibernate.hql.internal.ast.tree.FromElement.setAllPropertyFetch(boolean)" because "fromElement" is null

• My tables

  • Person
    • int id
    • text name
    • int job_id (foreign key with table JOB(id))
  • Job
    • int id
    • text name

• Entities

  @Entity
  @Table(name = "person")
  public class Person{
  
  @Id
  @Column(name = "id")
  int id;
  @Column(name = "name")
  String name;
  @Column(name = "job_id")
  int jobId;
  
  public int getId() {
      return id;
  }
  
  public void setId(int id) {
      this.id = id;
  }
  
  public int getJobId() {
      return jobId;
  }
  
  public void setJobId(int jobd) {
      this.jobId= jobId;
  }
  public String getName() {
      return name;
  }
  
  public void setName(int name) {
      this.name= name;
  }
  
  
  @Entity
  @Table(name = "job")
  public class Job{
  
  @Id
  @Column(name = "id")
  int id;
  @Column(name = "name")
  String name;
  
  public int getId() {
      return id;
  }
  
  public void setId(int id) {
      this.id = id;
  }
  
  public String getName() {
      return name;
  }
  
  public void setName(int name) {
      this.name= name;
  }
  

  • DAO

      public class PersonDAO {
      @Autowired
      private SessionFactory sessionFactory;
  
      public void setSessionFactory(SessionFactory sf) {
          this.sessionFactory = sf;
      }
  
      public List<Person> getAllPerson() {
          Session session = this.sessionFactory.getCurrentSession();
          List<PersonResponse> list = session.createQuery("from Person p left join p.jobId").list();
      }
  }
  
  - PersonResponse
      - POJO with Person parameteres/variables without annotations and job name.
  

Answer 1

To be able to use left join in hql you should correct your mapping for Person in the following way:

@Entity
@Table(name = "person")
public class Person
{
   @ManyToOne
   @JoinColumn(name = "job_id")
   Job job;

   // ...
}

and then you will be able to write hql query like this:

List<Person> list = session.createQuery("select p from Person p left join p.job").list();