当子实体有复合主键时，如何在父实体中定义@OneTomany？

Question

我的parent类有两个子类:child和parenthobby。子类有一个单数PK，其上的@OneTomany映射起作用。问题是我不知道如何将它映射到ParentHobby类上，这个类有一个复合PK。

家长：

//this works
@OneToMany(cascade = CascadeType.ALL, mappedBy = "parent", fetch = FetchType.EAGER)
private List<Child> childList;

//this DOES NOT work
@OneToMany(cascade = CascadeType.ALL, mappedBy = "parent", fetch = FetchType.EAGER)
private List<ParentHobby> hobbyList;

@Entity
@Table(name="CHILD")
public class Child {


    @Id
    @SequenceGenerator(name="CHILD_SEQ", sequenceName="CHILD_DB_SEQ", allocationSize = 1)
    @GeneratedValue(strategy=GenerationType.SEQUENCE, generator="CHILD_SEQ")
    @Column(name="CHILD_ID")
    private long childID;

    @JoinColumn(name = "PARENT_ID", referencedColumnName = "PARENT_ID", insertable = true, updatable = true)
    @ManyToOne(optional = true)
    private Parent parent;

@entity@table(name=“parent_hobby”）公共类ParentHobby{

@EmbeddedId
private ParentHobbyPK id;

ParentHobBypk：

@Embeddable
public class ParentHobbyPK {

    @JoinColumn(name = "PARENT_ID", referencedColumnName = "PARENT_ID", insertable = true, updatable = true)
    @ManyToOne(optional = true)
    private Parent parent;

    @Column(name="HOBBY_ID")
    private String hobbyID;

我在编译时遇到的例外情况是：

mappedBy reference an unknown target entity property: ParentHobby.parent in Parent.hobbyList

当子实体具有复合主键时，如何在父实体中定义@OneTomany关系？

_相似:

@OneTomany关系与复合键

JPA复合密钥@OneTomany

Answer 1

您需要使用派生标识。

parenthobbypk应如下所示：

@Embeddable
public class ParentHobbyPK {
    @Column(name="HOBBY_ID")
    private String hobbyID;
    private long parentID; // corresponds to the PK type of Parent
}

parenthobby应该如下所示（重要的是@mapsid注释）：

@Entity
@Table(name="PARENT_HOBBY")
public class ParentHobby {
    @EmbeddedId
    private ParentHobbyPK id;

    @MapsId("parentID") // maps parentID attribute of the embedded ID
    @ManyToOne(optional = true)
    @JoinColumn(name = "PARENT_ID", referencedColumnName = "PARENT_ID", insertable = true, updatable = true)
    private Parent parent;

    ...
}

派生标识在JPA2.1规范第2.4.1节中讨论。