Hibernate -多对多关系:关系表不会被填充

Question

我有一个名为Node的类，它可以有许多等级。一个等级可以与许多Node对象相关联。多对多。我的注释如下:

@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;
  }
}

//这里是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;
  }
}

当然，这两个类都有@Id注释。如。对于等级实体，它将是:

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

我的成绩表有5行，当与节点对象建立关系时将引用其中的一个子集。我使用下面的查询来创建节点和等级之间的关系。

// 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();

但这只保存节点对象，但这并不写到我的表"node_grade"我错过了什么?

即使我尝试保存grade对象，它也不会在node_grade中保存关系。

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

有什么问题吗?

Answer 1

您正在修改关联的反向。Hibernate只关心所有者端。

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