#OneToMany relationship issue while saving multiple values in Hibernate and Spring - spring

Question

I have two entities with #OneToMany bidirectional relationship as below:
#Entity
public class Company {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Integer companyId;
private String name;
#OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER, mappedBy="company")
Set<Employee> employees = new LinkedHashSet<>();
Employee class
#Entity
public class Employee {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Integer empId;
private String name;
private String address;
private String email;
#ManyToOne
#JoinColumn(name="companyId")
Company company;
Intially i saved 2 employees as below:
Employee emp= new Employee();
emp.setName("John");
emp.setEmail("John#gmail.com");
employeeRepository.save(emp);
Employee emp2= new Employee();
emp2.setName("Smith");
emp2.setEmail("smith#gmail.com");
employeeRepository.save(emp2);
Now I want to save one employee working for 2 different companies like below:
Company company =new Company();
company.setName("Google");
Employee emp = employeeRepository.findOne(1);
company.getEmployees().add(emp);
emp.setCompany(company);
companyRepository.save(company);
Company company2 =new Company();
company2.setName("Microsoft");
company2.getEmployees().add(emp);
emp.setCompany(company2);
companyRepository.save(company2);
It is updating only second company id into employee table. I want both the companies to be assigned to that employee. How can I do that?

Answer 1

The issue here is that you have a one-to-many when obviously it should be a many-to-many, viz. an employee can work for more than one company and a company has many employees.
You can either change the relationship to a #ManyToMany (and use #JoinTable if required) or you can create another entity, say, CompanyEmployee to which both Employee and Company have a one-to-many-relationship. The latter approach is probably preferable as you can then record additional information about the association e.g. start_date, end-date etc.
#Entity
#Table(name = "company_employees")
public class CompanyEmployee {
#ManyToOne
private Employee employee;
#ManyToOne
private Company company;
private Date startDate;
private Date endDate;
}