Model Look up table for a JPA Entity Field - jpa

Question

I'm trying to find out the appropriate relationship to be used in order to model an JPA Entity Field which needs a Look-up table (Comboxbox equivalent on the UI) to select the value from. An example below:
#Entity
public class Employee {
#Id
private int employeeId;
private String name;
private Department department;
}
#Entity
public class Department {
#Id
private int id;
private String name;
}
The instances of Department could be as follows:
Id | Name
-----------------------
100 | Human Resources
101 | Sales
102 | Finances
For an employee, the department field should get a value from one of the above. What should be the JPA annotations for the corresponding fields in both the entities?
Thanks,
Sandeep Joseph

Answer 1

I think you are looking for a unidirectional ManyToOne relationship from Employee to Department, something like this:
#Entity
public class Employee {
#Id
private int employeeId;
private String name;
#ManyToOne
#JoinColumn(name = "department_id", nullable = false)
private Department department;
}
This means an employee must be associated to a single department and a department can be associated to many employees.
If you need to know the list of employees associated to a department then you can make the relationship bidirectional by adding this:
#Entity
public class Department {
#Id
private int id;
private String name;
#OneToMany(mappedBy = "department")
private Collection<Employee> employees;
}