Spring Data一对多映射
我尝试在Spring Data项目中配置OneToMany和ManyToOne映射，但有一些问题。
所以我有两个实体：雇主和项目。 一个雇主可以有很多项目。
实体类：
Employer.java
@Entity
@Table (name="Employer")
public class Employer {
@Id
@SequenceGenerator(name="my_seq", sequenceName="GLOBAL_SEQUENCE")
@GeneratedValue(strategy = GenerationType.SEQUENCE ,generator="my_seq")
@Column (name="employer_id")
private int id;
@Column (name="name")
private String name;
@JoinColumn (name="employer_id")
@OneToMany(mappedBy = "employer", cascade = CascadeType.ALL, fetch = FetchType.EAGER)
private Set<Project> project = new HashSet<Project>();
......................
}
Project.java
@Entity
@Table (name="Project")
public class Project {
@Id
@SequenceGenerator(name="my_seq", sequenceName="GLOBAL_SEQUENCE")
@GeneratedValue(strategy = GenerationType.SEQUENCE ,generator="my_seq")
@Column (name="project_id")
private int id;
@Column (name="name")
private String name;
@ManyToOne
@JoinColumn(name="employer_id", nullable = false)
private Employer employer;
......................
}
存储库类：
public interface EmployerRepository extends JpaRepository<Employer, Integer> {
}
public interface ProjectRepository extends JpaRepository<Project, Integer> {
}
服务：
@Service
public class EmployerServiceImpl implements EmployerService {
@Autowired
private EmployerRepository employerRepository;
@Override
public List<Employer> getAllEmployers() {
return employerRepository.findAll();
}
}
@Service
public class ProjectServiceImpl implements ProjectService {
@Autowired
private ProjectRepository projectRepository;
@Override
public List<Project> getAllProjects() {
return projectRepository.findAll();
}
}
控制器：
@Controller
public class MainController {
private EmployerService employerService;
private ProjectService projectService;
@Autowired(required = true)
@Qualifier(value = "employerService")
public void setEmployerService(EmployerService employerService) {
this.employerService = employerService;
}
@Autowired(required = true)
@Qualifier(value = "projectService")
public void setProjectService(ProjectService projectService) {
this.projectService = projectService;
}
@RequestMapping(value="/employers", method=RequestMethod.GET)
public @ResponseBody List<Employer> getEmployers(@RequestParam(value = "name", required = false) String name) {
return employerService.getAllEmployers();
}
..............................
}
雇主表格：
EMPLOYER_ID . NAME
......................
1 . Google
2 . Oracle
3 . Facebook
项目表：
PROJECT_ID . NAME . EMPLOYER_ID
.......................................
1 . Create web site . 1
2 . Create reporting . 2
3 . Create web service . 3
4 . Fixing web site . 1
我期待着这样的事情：
[{"id":1,"name":"Google","project":[{"id":1,"name":"Create web site"}, {"id":4,"name":"Fixing web site"}},
{"id":2,"name":"Oracle","project":{"id":2,"name":"Create reporting"}},
{"id":3,"name":"Facebook","project":{"id":3,"name":"Create web service"}}]
但是controller类的getEmployers方法返回这一个：
[{"id":1,"name":"Oracle","project":[{"id":4,"name":"Fixing web site",
"employer":{"id":1,"name":"Oracle","project":[{"id":4,"name":"Fixing web site",
"employer":{"id":1,"name":"Oracle","project":[{"id":4,"name":"Fixing web site",
"employer":{"id":1,"name":"Oracle","project":[{"id":4,"name":"Fixing web site",
"employer":{"id":1,"name":"Oracle","project":[{"id":4,"name":"Fixing web site",
"employer":{"id":1,"name":"Oracle","project":[{"id":4,"name":"Fixing web site","employer":
...................
如果这个问题讨论了很多次，请抱歉，但我没有找到任何合适的答案。
提前致谢！
您有Employer和Project s之间的双向联系。 另外，你已经配置了要加载的关联的两边EAGER ly（默认情况下@ManyToOne关联被获取EAGER ly，并且你也迫使@OneToMany一边被获取EAGER ly）。 由于这种配置，当序列化框架加载Employer ，它会找到有效的Project ，这些Project具有与Employer的反向链接并最终陷入循环循环。
为了得到你想要的结果，你必须将@ManyToOne标记为@ManyTone(fetch = FetchType.LAZY)标记为LAZY ly（在Project实体上@ManyTone(fetch = FetchType.LAZY) 。
添加@JsonManagedReference在关系的前面部分（即User.java类）中：
@Entity
public class User implements Serializable {
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
private long id;
@Column(name="name")
private String name;
@ManyToMany
@JoinTable(name="users_roles",joinColumns=@JoinColumn(name = "user_fk"), inverseJoinColumns=@JoinColumn(name = "role_fk"))
@JsonManagedReference
private Set<Role> roles = new HashSet<Role>();
...
添加@JsonBackReference在关系的后面部分（即Role.java类）：
@Entity
public class Role implements Serializable {
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
private int id;
@ManyToMany(mappedBy="roles")
@JsonBackReference
private Set<User> users = new HashSet<User>();
...
这对我很好。 :-)
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