Question

我有实体结构：

@Entity
@Table(name = "users")
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", updatable = false, nullable = false)
    private Long id;

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "user", cascade = { CascadeType.ALL })
    List<UserAgreement> userAgreements= new ArrayList<>();

}

@Entity
@Table(name = "user_agreements")
public class UserAgreement {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", updatable = false, nullable = false)
    private Long id;

    @ManyToOne(cascade = CascadeType.REFRESH)
    @JoinColumn(name = "user_id")
    private User user;

    @ManyToOne(cascade = CascadeType.REFRESH)
    @JoinColumn(name = "agreement_id")
    private Agreement agreement;
}


@Entity
@Table(name = "agreements")
public class Agreement {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", updatable = false, nullable = false)
    private Long id;

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "agreement", cascade = { CascadeType.ALL })
    List<UserAgreement> userAgreements = new ArrayList<>();
}

我正在使用Spring Boot和JpaRepository。当我使用AgreementRepository extends JpaRepository<Agreement, Long>来保存协议和相关的UserAgreement时，它运行良好并将必要的字段级联到DB：

agreement.getUserAgreements().add(new UserAgreement(user, agreement, status));
agreementRepository.save(agreement);

但是，保存后，如果尝试检索user.getActiveUserAgreements()，我会得到空列表。它没有刷新。

如何强制用户实体获取从另一方保存的List<UserAgreement>？

Answer 1

来自Wikibooks: OneToMany

这种关系是双向的，因为应用程序更新了一个关系的一面，对方也应该得到更新，并且同步。在JPA中，与Java一样，它的责任在于应用程序，或维护关系的对象模型。如果你的应用程序添加到关系的一方，然后它必须添加到了另一边。

这意味着您需要在创建关系时将UserAgreement分配给User。

Answer 2

看起来像多对多关联。您可能可能会删除UserAgreement类。无论如何，为了支持它，你必须编写辅助方法addAgreement（），removeAgreement（）等。在这里查看更多细节https://vladmihalcea.com/the-best-way-to-use-the-manytomany-annotation-with-jpa-and-hibernate/

OneToMany不返回从其他实体保存的值

2 个答案: