jpa/hibernate/pg映射问题

我有两个实体,实体1和实体2,一对多关系。在Entity1上,我有一个包含条目的映射。

我用于在地图上保留带有某些实体2的新实体1的代码如下:

   Entity1 e1 = new Entity1();  
   Entity2 e2 = null;  
   e1.setE2s(new HashMap<String, Entity2>());
   for (String key : someKeySet()){
      e2 = new Entity2();
      e2.setCode(key);                      
      e2.setSwhon(true);        
      e2.setE1(e1);
      e1.getE2s(key, e2);       
      em.persist(e1.getE2s().get(key));         

    }       
    em.persist(e1);
    em.flush();

这是实体的一个例外:

@Entity
@Table(name = "wm_Entities1")  
public class Entity1 implements Serializable {  
   private static final long serialVersionUID = 6592708276573465599L;  
   private Map<String, Entity2> e2s;
   private Long id;  
   @Id  
   @GeneratedValue(strategy=GenerationType.TABLE)  
   public long getId() {  
    return id;  
   }  
   public void setId(long id) {  
    this.id = id;  
   }  
   public void setE2s(Map<String, Entity2> e2s){    
    this.e2s = e2s;
   }       
   @OneToMany(mappedBy = "e1", fetch = FetchType.EAGER)  
   public Map<String, Entity2> getE2s() {  
    return e2s;  
   }  
}

@Entity
@Table(name = "wm_Entities2")
public class Entity2 implements Serializable {  
    private static final long serialVersionUID = -6131765066573346790L; 
    private long id;
    private Entity1 e1;
    @Id
    @GeneratedValue(strategy=GenerationType.TABLE)
    public long getId() {
        return id;
    }

    public void setId(long id) {
        this.id = id;
    }
    @ManyToOne()
    @JoinColumn(name="e1_id")
    public Entity1 getE1() {
        return this.e1;
    }
    public void setE1(Entity1 e1) {
        this.e1 = e1;
    }
}

这似乎工作得很好,因为它在pg数据库中插入了两个实体,但关键是它没有在数据库中创建保存e2的map key(理论上jpa生成这个key),所以当我取回e1,并尝试从中获取e2s映射时,我有一个:

javax.ejb.ejb异常: org.hibernate.hibernateexception:空 集合的索引列:

如何保存此mapkey??

注意:我在jpa/hibernate中使用javaee,运行jboss 4.2,使用pgsqdb。