How to access the JoinColumn variable directly in a Entity.

Question

I have the below two entities with @OneToMany relationship between them,
Employee*
@Entity
@Table(name="EMPLOYEE")
public class Employee {
     @Id
     int employee_id;
     String employee_name;
Can I uncomment this ???
     //int emp_department_id;
     @ManyToOne
     @JoinColumn(name="emp_department_id")
     Department department;
Department*
@Entity
@Table(name="DEPARTMENT")
public class Department {
     @Id
     int department_id;
     String department_name;
     @OneToMany(mappedBy="department")
     Set<Employee> employeesSet;
I only want to persist the Employee since I already have the Department data in Db,
*1.But, if i uncomment emp_department_id and try to do this,*
               Employee e1= new Employee();
               e1.employee_id=1;
               e1.employee_name="employee1";
               e1.emp_department_id=1;
I get,
Internal Exception: java.sql.SQLException: ORA-00957: duplicate column name
Error Code: 957
Call: INSERT INTO EMPLOYEE3 (EMPLOYEE_ID, EMP_DEPARTMENT_ID, EMPLOYEE_NAME, emp_department_id) VALUES (?, ?, ?, ?)
     bind => [4 parameters bound]
*2. Instead I have to do something like this,*
               Department d= new Department();
               d.department_id=1;
               d.department_name="Engineering";
               Employee e1= new Employee();
               e1.employee_id=1;
               e1.employee_name="employee1";
               e1.department=d;
Is there a way to uncomment Employee.emp_department_id and insert employee data using pt. 1 ???

Answer 1

Hello,
Yes you can uncomment out that line if you want the fk column value without having to travers the relationship. The problem you are hitting when you do is because you then have the "emp_department_id" field defined twice. The error you are getting is because EclipseLink is currently case sensitive by default, so the JPA defined column name default for the emp_department_id attribute of "EMP_DEPARTMENT_ID" isn't matching the @JoinColumn(name="emp_department_id") since they are different cases - you should change the @JoinColumn so it uses an upper case field name to be consistent, ie
@JoinColumn(name="EMP_DEPARTMENT_ID") or set the EclipseLink eclipselink.jpa.uppercase-column-names property to true. This will then have the two fields match and will give you a more appropriate exception, that the field has two writable mappings.
Then you need make one of them read-only by adding the insertable=false, updateable=false to the annotation. You probably want to change the relationship, and so I'd make the int as read-only.
Best Regards,
Chris