弹簧数据一对多映射
弹簧数据一对多映射
提问于 2015-07-01 21:29:15
我尝试在Spring数据项目中配置OneToMany和ManyToOne映射，但存在一些问题。
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();
}
}主计长：
@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：
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，来自getEmployers类的controller方法返回这个方法：
[{"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，请原谅，但我没有找到合适的答案。
提前感谢！
回答 2
Stack Overflow用户
回答已采纳
发布于 2015-07-02 03:21:34
您在Employers和Projects之间有一个双向关联，另外，您已经将关联的两边配置为加载EAGERly (默认情况下，@ManyToOne关联被取为EAGERly，并且强制@OneToMany端也被取回EAGERly )。由于这种配置，当序列化框架加载Employers时，它会找到具有指向Employers的反向链接的有效Projects，并最终陷入循环循环。
为了获得所需的结果，必须将@ManyToOne端(在Project实体上)标记为LAZYly为@ManyTone(fetch = FetchType.LAZY)。
Stack Overflow用户
发布于 2017-04-07 13:25:59
在关系的前一部分(即User.java类)中添加@JsonManagedReference：
@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>();
...在关系的后面部分(即Role.java类)中添加@JsonBackReference：
@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>();
...这对我很管用。:-)
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原文链接：
https://stackoverflow.com/questions/31172021
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