無法獲取的對象集合中的許多一對多從數據庫

Question

關係，我在休眠以下層次：

@Entity 
@Table(name = "elements") 
@Inheritance(strategy=InheritanceType.JOINED) 

public abstract class Elements implements Serializable { 

    private static final long serialVersionUID = 1L; 

    @Id 
    @GeneratedValue(strategy = GenerationType.IDENTITY) 
    @Basic(optional = false) 
    @Column(name = "idelement") 
    private Integer idElement; 

    @ManyToMany(cascade = CascadeType.PERSIST, mappedBy = "elementsCollection") 
    private Collection<ElementsGroups> elementsGroupsCollection; 

    . 
    . 
    More attributes, constructor and getter/setter 
    . 
    . 
} 

@Entity 
@Table(name = "valves") 
@PrimaryKeyJoinColumn(name="idelement") 
@XmlRootElement 
public class Valves extends Elements { 

    @Basic(optional = false) 
    @Column(name = "position") 
    private int position; 

    @Basic(optional = false) 
    @Column(name = "status") 
    private boolean status; 

    . 
    . 
    More attributes, constructor and getter/setter 
    . 
    . 
} 

@Entity 
@Table(name = "elementsgroups") 
@XmlRootElement 
public class ElementsGroups implements Serializable { 

    private static final long serialVersionUID = 1L; 

    @Id 
    @GeneratedValue(strategy = GenerationType.IDENTITY) 
    @Basic(optional = false) 
    @Column(name = "idgroup") 
    private Integer idGroup; 

    @Basic(optional = false) 
    @Column(name = "description") 
    private String description; 

    @ManyToMany(cascade = {CascadeType.PERSIST}) 
    @JoinTable(name="joinelementsgroups", joinColumns={@JoinColumn(name="idgroup")}, inverseJoinColumns={@JoinColumn(name="idelement")}) 
    private Collection<Elements> elementsCollection; 

    . 
    . 
    More attributes, constructor and getter/setter 
    . 
    . 
} 

的想法是有一個「元素」超包裹的一堆元素該系統共享一些特徵和功能。這些元素可以分成幾組。這是數據庫結構：

當我堅持了Valve子類的對象，並將其添加到一個組，我可以看到在數據庫中的變化。事情是這樣的：

SessionFactory sf = new Configuration().configure().buildSessionFactory(); 

    Session s = sf.openSession(); 
    Transaction tx = s.beginTransaction(); 
    Valve v1 = new Valve(); 
    Valve v2 = new Valve(); 
    s.save(v1); 
    s.save(v2); 
    tx.commit(); 

    tx = s.beginTransaction(); 
    LinkedList<Elements> valves = new LinkedList<>(); 
    valves.add(v1); 
    valves.add(v2); 
    ge.setElementsCollection(valves); 

    s.save(ge); 
    tx.commit(); 

//Database: OK 

當我拿到Valve對象，我可以得到該對象所屬的組，通過它的getter方法。當我試圖讓ElementsGroups對象，在那裏我可以得到它的所有屬性出現問題，但elementsCollection是不是含有Valve前加入空：

tx = s.beginTransaction(); 
    Valve v1 = (Valve)s.get(Valve.class, 3); 
    for(ElementsGroups g : v1.getElementsGroupsCollection()) 
     System.out.println("Valve belongs to: " + g); 

    ElementsGroups ge = (ElementsGroups)s.get(ElementsGroups.class, 1); 
    System.out.println("Group number of elements: " + ge.getElementsCollection().size()); 

    tx.commit(); 

輸出：

Valve belongs to: model.ElementsGroups[ idgroup=1 ] 
Group number of elements: 0 

我有已經實現的類似的關係不會顯示這個問題，所以我猜這個問題可能與類的層次結構有關，但我是Hibernate的新手，不知道我是否錯過了某些東西。

PS：請注意，我DROP掉的代碼的幾個部分，以方便其閱讀，但我可以添加必要時

Answer 1

我想你忘記了與ElementGroups實體來填充閥門實體，從而使雙方都引用彼此之間：

tx = s.beginTransaction(); 
    LinkedList<Elements> valves = new LinkedList<>(); 

    Valve managedV1 = s.merge(v1); 
    Valve managedV2 = s.merge(v2); 

    valves.add(managedV1); 
    valves.add(managedV2); 

    managedV1.getElementsGroupsCollection().add(ge); 
    managedV2.getElementsGroupsCollection().add(ge); 

    ge.setElementsCollection(valves); 

    s.save(ge); 
    tx.commit(); 

另外我想你應該在第二筆交易中首先合併閥門。