how to Fix spring boot one to many bidirectional i

问题:

i am try to create a one to many bidirectional mapping using spring boot and spring data jpa please look the below entity

Employer Entity

@Entity  
public class Employer  
{  
private Long id;  
private String employerName;  
private List<Employee> employees;  

@Id  
@GeneratedValue(strategy=GenerationType.AUTO)  
public Long getId()  
{  
    return id;  
}  
public void setId(Long id)  
{  
    this.id = id;  
}  
public String getEmployerName()  
{  
    return employerName;  
}  
public void setEmployerName(String employerName)  
{  
    this.employerName = employerName;  
}  

@OneToMany(cascade=CascadeType.ALL, mappedBy="employer")  
public List<Employee> getEmployees()  
{  
    return employees;  
}  
public void setEmployees(List<Employee> employees)  
{  
    this.employees = employees;  
}  
} 

Employee Entity

@Entity  
public class Employee  
{  
private Long id;  
private String employeeName;  
private Employer employer;  

@Id  
@GeneratedValue(strategy=GenerationType.AUTO)  
public Long getId()  
{  
    return id;  
}  
public void setId(Long id)  
{  
    this.id = id;  
}  
public String getEmployeeName()  
{  
    return employeeName;  
}  
public void setEmployeeName(String employeeName)  
{  
    this.employeeName = employeeName;  
}  
@ManyToOne(cascade=CascadeType.ALL, fetch = FetchType.LAZY)  
public Employer getEmployer()  
{  
    return employer;  
}  
public void setEmployer(Employer employer)  
{  
    this.employer = employer;  
}  
}  

Employer Repo

public interface EmployerServices extends JpaRepository<Employer, Long> {
}

Employee Repo

public interface EmployeeServices extends JpaRepository<Employee, Long> {
}

REST Controller is

 @RestController
 public class Controller {
 @Autowired EmployeeServices employeeServices;
 @Autowired EmployerServices employerServices;
 @GetMapping("/getempr")
 public Object getempr(){
    return employerServices.findOne(1L);
 }
}

now the problem begin start see my out put

its look like a infighting loop and my server throwing error getOutputStream() has already been called for this response.

 I used @JsonBackReference & @JsonManagedReference 

annotation but the problem is its working like one to many

 {
   "id":1,
   "employerName":"employer",
   "employees":[
     {"id":1,"employeeName":"emp1"},
     {"id":2,"employeeName":"emp2"}
   ]
}  

if I am trying to get in the concern of many to one like all employee with employer. the output is

 [
  {
   "id":1,
   "employeeName":"emp1"
  },
  {
    "id":2,
    "employeeName":"emp2"}
 ]

its not showing me the employer details.

please suggets me guys what i am doing wrong. thanks in advance!!

回答1:

with the JSON its a problem with bi-directional mapping. Use the below properties.

@JsonIgnoreProperties("employer")
@JsonIgnoreProperties("employees")

please keep fetching type as eager.

hope this will work.

回答2:

Instead of using @JsonBackReferenceand @JsonManagedReference try to use annotation @JsonIgnoreProperties:

@JsonIgnoreProperties("employer")
private List<Employee> employees;  

@JsonIgnoreProperties("employees")
private Employer employer;  

It prevents Jackson from rendering a specified properties of associated objects.

回答3:

You can solve your issue with two modification with annotations.
Employer.class

@Entity
public class Employer {
    private Long id;
    private String employerName;

    @OneToMany(cascade = CascadeType.ALL,
            mappedBy = "employer",
            orphanRemoval = true)
    private List<Employee> employees;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getEmployerName() {
        return employerName;
    }

    public void setEmployerName(String employerName) {
        this.employerName = employerName;
    }

    public List<Employee> getEmployees() {
        return employees;
    }

    public void setEmployees(List<Employee> employees) {
        this.employees = employees;
    }
}

Employee.class

@Entity
public class Employee {
    private Long id;
    private String employeeName;


    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "employer_id")
    private Employer employer;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getEmployeeName() {
        return employeeName;
    }

    public void setEmployeeName(String employeeName) {
        this.employeeName = employeeName;
    }

    public Employer getEmployer() {
        return employer;
    }

    public void setEmployer(Employer employer) {
        this.employer = employer;
    }
}

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