CODEWITHSUNDEEP
javaspringhibernatejpaorm
Rose
Rose

Reputation: 2872

Hibernate - Many to many relationship: relationship table not getting populated

I've a class called Node that can have many Grades. And one grade can be associated with many Node objects. So many to many. my annotations are like the following:

@Entity
@Table(name="tbl_nodes")
public class Node {
 //getters setters, constructors.

  private Set<Grade> grades = new HashSet<Grade>();

  @ManyToMany(mappedBy = "nodes")
  public Set<Grade> getGrades() {
    return grades;
  }
}

// and here is grade class

@Entity
@Table(name="grades")
public class Grade {
  private Set<Node> nodes;
  // getters, setters, constructors

  @ManyToMany(cascade = CascadeType.ALL)
  @JoinTable(
      name = "node_grade",
      joinColumns = @JoinColumn(name = "grade_id"),
      inverseJoinColumns = @JoinColumn(name = "node_id")
  )
  public Set<Node> getNodes() {
    return nodes;
  }
}

both classes have @Id annotated ofcourse. For eg. for grade entity it would be:

  @Id
  @GeneratedValue
  @Column(name="grade_id")
  public int getId() {
    return id;
  }

My grade table has 5 rows and a subset of the rows will be referenced when the relationship is made with a node object. I'm using the following query to create a relation between node and grade.

// loads configuration and mappings
    Configuration configuration = new Configuration().configure();
    ServiceRegistryBuilder registry = new ServiceRegistryBuilder();
    registry.applySettings(configuration.getProperties());
    ServiceRegistry serviceRegistry = registry.buildServiceRegistry();

    // builds a session factory from the service registry
    SessionFactory sessionFactory = configuration.buildSessionFactory(serviceRegistry);

    // obtains the session
    Session session = sessionFactory.openSession();
    session.beginTransaction();

    // List all grade 
    Query queryAllGrades = session.createQuery("FROM  Grade");
    List<Grade> allGrades = queryAllGrades.list();
    for(Grade grade: allGrades) {
      System.out.println("Grade::" + grade.getName());
    }

// Create a new Node
    Node node = new Node();
    node.addGrade(allGrades.get(0));

    session.save(node);

    session.getTransaction().commit();
    session.close();

But this only saves the Node object but this doesn't write to my table "node_grade" What am I missing?

even if I try to save the grade object it doesn't save the relationship in node_grade.

session.save(allGrades.get(0)); //doesn't save either the node or the node_grade

session.saveOrUpdate(allGrades.get(0)); //doesn't save either the node or the node_grade

What could be the issue?

Upvotes: 0

Views: 848

Answers (1)

JB Nizet
JB Nizet

Reputation: 691625

You're modifying the inverse side of the association. Hibernate only cares about the owner side.

Node node = new Node();
session.save(node);
allGrades.get(0).addNode(node);

Upvotes: 1

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