当子有复合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类具有单个PK，并且其@OneToMany上的映射有效。问题是我不知道如何将其映射到具有复合PK的ParentHobby类。

上级：

//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;

儿童：

@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;

我在编译时遇到的异常是：

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

当子有复合主键时，如何在父实体中定义@OneToMany关系？

Answer 1

您需要使用派生身份。

ParentHobbyPK 应该看起来像这样：

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

ParentHobby应该看起来像这样（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;

    ...
}

派生身份将在JPA 2.1规范的第2.4.1节中讨论。