Question

我很担心为什么JPA会创建两个多对多而不是两个一对多的关系。我有班级作者和两套手机和电子邮件。

@Entity
public class Author {

    @Id
    @GeneratedValue
    private int id;

    private String firstName;

    private String lastName;

    @OneToMany(cascade = CascadeType.PERSIST, fetch = FetchType.EAGER)
    private Set<Phone> phones;

    @OneToMany(cascade = CascadeType.PERSIST, fetch = FetchType.EAGER)
    private Set<Email> emails;

和两个班级

@Entity
public class Phone {

    @Id
    @GeneratedValue
    private int id;

    private String number;

    @ManyToOne
    @JoinColumn(name = "author_fk_phone_id")
    private Author author;

@Entity
public class Email {

    @Id
    @GeneratedValue
    private int id;

    private String email;

    @ManyToOne
    @JoinColumn(name = "author_fk_id")
    private Author author;

因此JPA应该创建Author，Phone，Email表，但JPA还会创建author_email，author_phone表。我很困惑。

Answer 1

您的JPA提供程序会创建其他表（author_email和author_phone），因为您具有双向关系，但您没有指出这些关系的哪一方是所有者（mappedBy属性）。

对Author类中的集合进行以下更改，它应该按预期工作。

@OneToMany(cascade = CascadeType.PERSIST, fetch = FetchType.EAGER, mappedBy = "author")
private Set<Phone> phones;

@OneToMany(cascade = CascadeType.PERSIST, fetch = FetchType.EAGER, mappedBy = "author")
private Set<Email> emails;

多对多而不是一对多

1 个答案: