当孩子有复合PK时，如何在父实体中定义@OneToMany？

Question

我的Parent班级有两个子班级： Child和ParentHobby. Child 类有一个单一的 PK 并且@OneToMany它的映射有效。问题是我不知道如何将它映射到具有复合 PK 的 ParentHobby 类上。

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;

孩子：

@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;

家长爱好：

@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;

我在编译时得到的异常是：

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？

_相似的：

@OneToMany 与复合键的关系

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JPA复合键@OneToMany

Answer 1

You need to use a derived identity.

ParentHobbyPK should look like this:

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

ParentHobby should look like this (the important thing being the @MapsId annotation):

@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;

    ...
}

派生身份在 JPA 2.1 规范的第 2.4.1 节中讨论。