Relationship in Spring-jpa Infinite recursion - jackson

Question

I have two tables Department and Employees. Department is parent of Employee and both are joined by department_id.
Department
#Entity
public class Department {
#Override
public String toString() {
return "Department [departmentId=" + departmentId + ", departmentName=" + departmentName + "]";
}
#Id
public Integer departmentId;
public String departmentName;
#OneToMany(mappedBy = "department",fetch=FetchType.LAZY)
public Set<Employee> employees;
}
Employee
#Entity
public class Employee {
#Override
public String toString() {
return "Employee [employee_id=" + employeeId + ", employee_name=" + employeeName + ", department="
+ department + "]";
}
#Id
public Integer employeeId;
public String employeeName;
#ManyToOne
#JoinColumn(name = "departmentId")
public Department department;
}
When I am trying to retrieve all department details it is creating a cyclic dependency and jackson is throwing the following error . So I would like to know how is this case handled where you need flexibility to access the child details from parent and access parent details from child.
2017-08-01 12:03:13.245 WARN 18197 --- [o-auto-1-exec-3]
.w.s.m.s.DefaultHandlerExceptionResolver : Failed to write HTTP message:
org.springframework.http.converter.HttpMessageNotWritableException: Could not
write JSON: Infinite recursion (StackOverflowError); nested exception is
com.fasterxml.jackson.databind.JsonMappingException:

Answer 1

I was able to achieve this solution using the following approach #JsonIgnoreProperties. By using this way i was able to fetch employee details in department and department level details in employees and avoiding infinite recursion
#JsonIgnoreProperties("department")
#OneToMany(mappedBy = "department",fetch=FetchType.EAGER)
public Set<Employee> employees;
#JsonIgnoreProperties("employees")
#ManyToOne
#JoinColumn(name = "departmentId")
public Department department;

Answer 2

You can use #JsonManagedReference and #JsonBackReference :
#JsonBackReference
public Department department;
and in Department Model
#JsonManagedReference
public Set<Employee> employees
It should work now :)

Answer 3

Yes this is expected, Jackson will iterate over your references and since the relation is bidirectional it will get stuck in an infinite operation.
To solve this you can use #JsonIgnore to ignore serializing one side of the relation to break the loop
#Entity
public class Employee {
#Override
public String toString() {
return "Employee [employee_id=" + employeeId + ", employee_name=" + employeeName + ", department="
+ department + "]";
}
#Id
public Integer employeeId;
public String employeeName;
#JsonIgnore
#ManyToOne
#JoinColumn(name = "departmentId")
public Department department;
}