Spring Data JPA Hibernate - @ManyToOne 关系中出现的额外元素

Question

我有一些实体类具有一对多 - 多对一的关系。我正在使用 Spring 和 Hibernate。

每个TwoWayService 在我的应用程序中恰好有2 个Services。

摘录：

@Entity
@Table(name = "two_way_services")
public class TwoWayService  {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;

    @Column
    private String name;

    @OneToMany(cascade = CascadeType.ALL, 
               mappedBy = "twoWayService", 
               fetch = FetchType.EAGER)
    private List<Service> services;

    public TwoWayService() {    
        services = new ArrayList<>();   
        // Add two as default 
        services.addAll(Arrays.asList(new Service(), new Service()));
    }

    public void setService1(Service service) {
        services.set(0, service);
        service.setTwoWayService(this);
    }

    public void setService2(Service service) {
        services.set(1, service);
        service.setTwoWayService(this);
    }

    ...
}

@Entity
@Table(name = "services")
public class Service {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;

    @Column
    private String name;

    @ManyToOne(optional = false)
    @JoinColumn
    private TwoWayService twoWayService;

    public void setTwoWayService(TwoWayService twoWayService) {
        this.twoWayService = twoWayService;
    }

    ...
}

我在后端使用 Derby。数据库架构是这样的：

CREATE TABLE two_way_services (
  id INT NOT NULL PRIMARY KEY GENERATED ALWAYS AS IDENTITY (START WITH 1, INCREMENT BY 1),
  config_name VARCHAR(255) NOT NULL,
  name VARCHAR(80),
  admin_ip VARCHAR(32) NOT NULL,
  connection_state INT NOT NULL
);

CREATE TABLE  services (
  id INT NOT NULL PRIMARY KEY GENERATED ALWAYS AS IDENTITY (START WITH 1, INCREMENT BY 1),
  name VARCHAR(80),
  type INT NOT NULL,
  ruleset VARCHAR(255) NOT NULL,
  two_way_service_id INT,
  FOREIGN KEY (two_way_service_id) REFERENCES two_way_services(id) ON DELETE CASCADE
);

仓库界面：

public interface TwoWayServiceRepository extends Repository<TwoWayService, Integer> {
    <S extends T> S save(S entity);

    ...
}

在我的单元测试中，我发现当我在 TwoWayService 上调用 findOne 时，我发现我有 4 个 Services 而不是 2 个。浏览数据库直接显示了我所期望的数据。

TwoWayService tws1 = repo.findOne(1); // get by id
assertThat(tws1.getServices().size()).isEqualTo(2); // fails, expected:<[2]> but was:<[4]>

在调试器中检查它，我在services 列表中看到了 4 个元素：我期望的两个元素，加上 2 个额外的元素，它们是预期的副本。我不明白这些是从哪里来的。为什么这些额外的对象会出现在列表中？

Answer 1

我不确定，但我认为，这是因为您在构造函数中添加了 2 个服务，在每个 setter 中添加了 1 个。这总共有 4 个。您测试服务的数量，这是您想要测试的吗？