Java 如何在JPA2中创建映射为实体类的3路或4路多对多关联

我正在使用Spring3.1、Hibernate4.0.1.FINAL和SpringDataJPA1.0.2.RELEASE。假设我在

a类

和

B类

之间有一个

多对多

，映射为

ABMap

。我还有另一个介于

C类

和

D类

之间的多对多映射为

CDMap

。 我有一个类

ABMapID

annotated@embeddeble

@Embeddable
public class ABMapID{
   private String aID;
   private String bID;
}
//... setters and getters

下面是映射本身

 @Entity
 public class ABMap {

 @Id
@AttributeOverrides({
  @AttributeOverride(name = "aID", column = @Column(name = "a_id",insertable = false, updatable = false)),
  @AttributeOverride(name = "bID", column = @Column(name = "b_id", insertable = false,updatable = false))
})
private ABMapID ID;
@ManyToOne(targetEntity = A.class)
@JoinColumn(name = "a_id",insertable = false,updatable = false)
private A a;

@ManyToOne(targetEntity = B.class)
@JoinColumn(name = "b_id", insertable = false, updatable = false)
private B b;
//.... setters and getters  
}

现在，我们想将

ABMap

更改为

ACDMap

，其中

ACDMapID

由aID和CDMapID组成（CDMapID本身由cID组成，dID）。 所以我的新关联id是ACDMapID

 @Embeddable
 public class ACDMapID {
  private String aID;
  private CDMapID cdmapID;

} 

and the entity is mapped like so

@Entity
public class ACDMap {
   @Id
@AttributeOverrides({
  @AttributeOverride(name = "aID", column = @Column(name = "a_id",insertable = false, updatable = false)),
  @AttributeOverride(name = "cdmapID", column = @Column(name = "dcmap_id", insertable = false,updatable = false))
})
  private ACDMapID ID;

}

所以运行这个给我这个错误

原因：org.hibernate.AnnotationException:从ACDMap引用CDMap的外键的列号错误。应该是2

---

有没有办法做到这一点？我更愿意保留CDMap。你似乎不理解JPA的概念。您不应该以编程方式处理ID，而应该处理对象

您需要基于可嵌入对象中的ID的动态关联。也许这样的构造在普通Hibernate中是可能的，但在JPA中肯定不是

---

JPA的全部目的是让您处理对象，而不是数据库关系。一旦你开始混合这两个方面，地狱就会爆发，所以JPA的人决定不支持这种混合，我不能责怪他们。

我想我应该试一试，以下是结果（没有尝试过，所以这纯粹是理论上的）

@Entity
public class A
{
    @Id
    private Long id;

    @ManyToMany
    @JoinTable(name = "A_B", joinColumns={
        @JoinColumn(name = "a_id")
    }, inverseJoinColumns = {
        @JoinColumn(name = "b_id")
    })
    private Collection<B> collectionOfB;

    @ManyToMany
    @JoinTable(name = "A_C_D", joinColumns={
        @JoinColumn(name ="a_id")
    }, inverseJoinColumns = {
        @JoinColumn(name = "c_id"),
        @JoinColumn(name = "d_id")
    })
    private Collection<ACD> collectionOfCD;
}

@Entity
public class B
{
    @Id
    private Long id;

    @ManyToMany(mappedBy = "collectionOfB")
    private Collection<A> collectionOfA;
}

@Entity
public class C
{
    @Id
    private Long id;

    @ManyToMany
    @JoinTable(name = "C_D", joinColumns={
        @JoinColumn(name = "c_id")
    }, inverseJoinColumns = {
        @JoinColumn(name = "d_id")
    })
    private Collection<D> collectionOfD;
}

@Entity
public class D
{
    @Id
    private Long id;

    @ManyToMany(mappedBy = "collectionOfD")
    private Collection<C> collectionOfC;
}

@Entity
@Table(name = "C_D")
public class CD
{
    @EmbeddedId
    private CDPK key;

    @MapsId("cId")
    @ManyToOne
    private C c;

    @MapsId("dId")
    @ManyToOne
    private D D;
}

@Embeddable
public class CDPK
{
    @Column(name = "c_id")
    private Long cId;
    @Column(name = "d_id")
    private Long dId;
}

| A  |       | A_B         |      | B  |
| id |------<| a_id | b_id |>-----| id |
  |
  |
  |     | A_C_D              |
  \----<| a_id | c_id | d_id |
                 \/     \/
                 |      |
                 |      |
    | C  |     | C_D         |      | D  |
    | id |----<| c_id | d_id |>-----| id |