Hibernate实体可以与其他独立实体建立多个一对多关系吗？

Question

我有三个实体，比如A，B和C. A包含B和C的多个实例。从逻辑上讲，从A到B和A到C将有两个一对多的关系。行正在增加填充在表中，但B和C在外键列中没有A的ID。代码如下：

A类：

@Entity
public class A
{
 private int id;
 private B[] bSet = null;
 private C[] cSet = null;

 @Id
 @GeneratedValue(strategy = GenerationType.AUTO)
 public int getId()
 {return id;}

 @OneToMany(cascade = CascadeType.ALL, mappedBy = "a")
 @OrderColumn(name = "bIndex")
 public B[] getBset()
 {return bSet;}

 @OneToMany(cascade = CascadeType.ALL, mappedBy = "a")
 @OrderColumn(name = "cIndex")
 public C[] getCset()
 {return cSet;}
}

B组：

@Entity
public class B
{
 private int bId;
 private A a;

 @Id
 @GeneratedValue(strategy = GenerationType.AUTO)
 public int getBId()
 {return bId;}

 @ManyToOne(cascade = CascadeType.ALL)
 public A getA(A a)
 {return a;}
}

C类：

@Entity
public class C
{
 private int cId;
 private A a;

 @Id
 @GeneratedValue(strategy = GenerationType.AUTO)
 public int getCId()
 {return cId;}

 @ManyToOne(cascade = CascadeType.ALL)
 public A getA(A a)
 {return a;}
}

您可能会问为什么我也在A中设置OneToMany端的级联属性。但如果我不这样做，它会引发像这样的瞬态对象异常。

org.hibernate.TransientObjectException: object references an unsaved transient instance - save the transient instance before flushing: B

如果我这样做，异常消失，数据保存在H2数据库中，但B和C中的A列都获取空值。请帮帮我。

修改

我在这里添加了用于持久保存实体的方法。出于我的目的，我使所有实体都从一个普通的空类扩展，以便于使用。

public void populateObjects()
{
  HashMap<String,ArrayList<HibernateEntity>> persistentEntities = new HashMap<String, ArrayList<HibernateEntity>>();

  persistentEntities.put("A", new ArrayList<HibernateEntity>());
  persistentEntities.put("B", new ArrayList<HibernateEntity>());
  persistentEntities.put("C", new ArrayList<HibernateEntity>());

 A a = new A();
 a.bSet = new B[2];
 a.bSet[0] = new B();
 a.bSet[1] = new B();
 a.cSet = new C[1];
 a.cSet[0] = new C();

 persistentEntities.get("A").add(a);
 start();
 persistEntities(persistentEntities);
}


public synchronized boolean start() throws Exception
{
    if(isStarted)
        return isStarted;

    server = Server.createTcpServer();
    server.start();
    Properties prop = new Properties();
    String propFileName = "database.properties";
    InputStream inputStream = getClass().getClassLoader().getResourceAsStream(propFileName);
    prop.load(inputStream);

    if(inputStream == null)
    {
        throw new FileNotFoundException("Property file "+propFileName+" not found in classpath");
    }

    String dbPath = prop.getProperty("db_path");
    String dbName = prop.getProperty("db_name");
    System.out.println("Full database path: "+"jdbc:h2:file:"+dbPath+dbName);
    DriverManager.getConnection("jdbc:h2:file:"+dbPath+dbName);
    Configuration configuration = new Configuration();
    configuration.configure();
    serviceRegistry = new StandardServiceRegistryBuilder().applySettings(configuration.getProperties()).build();
    sessionFactory = configuration.buildSessionFactory(serviceRegistry);

    isStarted = true;
    return isStarted;
}


public void persistEntities(HashMap<String, ArrayList<HibernateEntity>> persistentEntities)
{
 Session session = openSession();
    Transaction transaction = session.beginTransaction();

    Set<String> keySet = persistentEntities.keySet();

    try
    {
        for(String key: keySet)
        {

            ArrayList<HibernateEntity> entities = persistentEntities.get(key);

            if(key.equalsIgnoreCase("A"))
            {
                if(entities.size() > 0)
                {
                    for(HibernateEntity h: entities)
                    {
                        A a = (A)h;
                        session.save(a);                       
                    }
                }

            }
            else if(key.equalsIgnoreCase("B"))
            {
                if(entities.size() > 0)
                {
                    for(HibernateEntity h: entities)
                    {
                        session.save((B)h);
                        System.out.println("Persisted "+key);
                    }
                }

            }
            else if(key.equalsIgnoreCase("C"))
            {
                if(entities.size() > 0)
                {
                    for(HibernateEntity h: entities)
                    {
                        session.save((C)h);
                        System.out.println("Persisted "+key);
                    }
                }

            }            
        }
        transaction.commit();
        System.out.println("Successfully committed");

    }
    finally
    {
        closeSession(session);
    }
}