Hibernate two parents one child mapping

Question

I have following scenario: There are companies and employees. Each company has a set of employees. Each employee can work for several companies. So I implemented following relationships:

Company.class:

@JoinTable(name = "company_employee", joinColumns = @JoinColumn(name = "company_id") , inverseJoinColumns = @JoinColumn(name = "employee_id") )
@ManyToMany(fetch = FetchType.LAZY)
private List<Employee> employees;

Employee.class:

@JoinTable(name = "company_employee", joinColumns = @JoinColumn(name = "employee_id") , inverseJoinColumns = @JoinColumn(name = "company_id") )
@ManyToMany(fetch = FetchType.LAZY)
private List<Company> companies;

Obviously, to work for several companies, each employee should have several not overlapping schedules assigned for each company he or she works. Also, there should be a list of schedules for each combination Company-Employee, as sometimes old schedule expires, and new schedule becomes effective. So I also have Schedule.class, which is supposed to have child to parent @ManyToOne relationships both to Company and Employee, and should work following way: each Schedule, and thus, List<Schedule> should correspond to exactly one combination of Company and Employee instances. How to implement this relationship?

Update 1

I only have in mind adding @OneToMany Schedule relationship to each Company and Employee, but then I need to put instances of Schedule both to Company and Employee each time, and this way just don't look right, also it's not obvious for me now how to fetch it back. So any help will be appreciated.

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This post was updated to show real-life scenario I have, not just generic Entity1, Entity2, Entity3 names for classes.

Update 2

I accepted the answer, but I cannot use it if Schedule contain Lists. According to my plan, Schedule should contain List<Vacation> to know the set of Vacations over a year, and List of Days, each of which shows start of particular week day, break, and end of this day. Those Days are also unique for each Schedule instance.

It was supposed to be something like below, but obviously now I don't have schedule_id, so how to connect those lists to Schedule?

@OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL, orphanRemoval = true) 
@JoinColumn(name = "schedule_id") 
private List<Vacation> vacations;

@JoinTable(name = "schedule_week", joinColumns = @JoinColumn(name = "schedule_id") , inverseJoinColumns = @JoinColumn(name = "day_id") )
@OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL, orphanRemoval = true) 
private List<Day> week;

How to include those lists right?

Answer 1

I would like to suggest the following solution.

An embeddable class that contains the Company and Employee for a particular schedule.

@Embeddable
public class ScheduleOwner implements Serializable{

    @MapsId("id")
    @ManyToOne(cascade = CascadeType.ALL)
    Company c;

    @MapsId("id")
    @ManyToOne(cascade = CascadeType.ALL)
    Employee e;
}

The Schedule class is embedding a ScheduleOwner instance.

@Entity
public class Schedule {

    @EmbeddedId
    ScheduleOwner owner;

    String description;
}

The Company and Employee classes(no change done to them)

@Entity
public class Company {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @JoinTable(name = "company_employee", joinColumns = @JoinColumn(name = "company_id") , inverseJoinColumns = @JoinColumn(name = "employee_id") )
    @ManyToMany(fetch = FetchType.LAZY)
    private List<Employee> employees;
}


@Entity
public class Employee {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @JoinTable(name = "company_employee", joinColumns = @JoinColumn(name = "employee_id") , inverseJoinColumns = @JoinColumn(name = "company_id") )
    @ManyToMany(fetch = FetchType.LAZY)
    private List<Company> companies;
}

UPDATE 1

Below is how you could save and fetch results.

  Employee e1 = new Employee();
  Company c1 = new Company();
  c1.employees.add(e1);

  e1.companies.add(c1);

  ScheduleOwner so = new ScheduleOwner();
  so.c = c1;
  so.e = e1;

  Schedule s = new Schedule();
  s.owner = so;

  session.save(c1);
  session.save(e1);
  session.save(s);

  // below query will fetch from schedule, where company id = 9
  Schedule ss = (Schedule) session.createQuery("From Schedule sh where sh.owner.c.id = 9").uniqueResult();

UPDATE 2

@Entity
public class Company {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @JoinTable(name = "company_employee", joinColumns = @JoinColumn(name = "company_id", referencedColumnName="id") 
                                        , inverseJoinColumns = @JoinColumn(name = "employee_id", referencedColumnName="id"))
    @ManyToMany(fetch = FetchType.LAZY)
    List<Employee> employees = new ArrayList<>();

    String name;
}

@Entity
public class Employee {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @ManyToMany(fetch = FetchType.LAZY, mappedBy = "employees")
    List<Company> companies = new ArrayList<>();

    String name;
}

@Entity
public class Schedule {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    int schedule_id;

    @ManyToOne
    @JoinColumn(name = "company_id", insertable = false, updatable = false)
    private Company company;
    @ManyToOne
    @JoinColumn(name = "employee_id", insertable = false, updatable = false)
    private Employee employee;

    String description;

    @OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL, orphanRemoval = true, mappedBy = "schedule")
    List<Vacation> vacations;

}

@Entity
public class Vacation {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int vacation_id;

    @ManyToOne
    @JoinColumn(name = "schedule_id" ) 
    Schedule schedule;

    @OneToMany(mappedBy = "vacation")
    List<Day> days;
}

Day entity directly relates to Vacation. Not to Schedule.

@Entity
public class Day {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;


    @ManyToOne
    @JoinColumn(name = "vacation_id")
    Vacation vacation;
}

Hope this helps.