How to create Hibernate Mapping for a self referencing table

Question

I was asked how I would create a hibernate mapping for a column in a table that refers to the primary key of the table.

For example, an Employee table has EMP_ID as primary key and it also has MGR_ID column to know the manager of the employee. As a manager is also an Employee, it would be in the same table. Hence every Employee row has a manager Id which is also an employee.

1. How do we create Hibernate Mapping for this Employee Class?
2. How would the Employee class look like? Does it have just a manager Id in it or it will contain another Employee Object as a member variable.

Kindly help me with this kind of scenario. Thank you.

Gracious

Answer 1

You can have a reference to the manager in your Employee class.

The entity looks like this:

@Entity
@Table(name="EMPLOYEE")
public class Employee {
     
    @Id
    @Column(name="EMPLOYEE_ID")
    @GeneratedValue
    private Long employeeId;
     
    @Column(name="FIRSTNAME")
    private String firstname;
     
    @Column(name="LASTNAME")
    private String lastname;
     
    @ManyToOne(cascade={CascadeType.ALL})
    @JoinColumn(name="manager_id")
    private Employee manager;
 
    @OneToMany(mappedBy="manager")
    private Set<Employee> subordinates = new HashSet<>();
 
    public Employee() {
    }
 
    public Employee(String firstname, String lastname) {
        this.firstname = firstname;
        this.lastname = lastname;
    }
         
    // Getter and Setter methods
}

Refer to this link for complete example:

Hibernate Self Join Annotations One To Many mapping example

Carmine

is this approach effective? Suppose, You have Director, Director have manager, manager have employee. So when you open an employee, you will get a manager, inside that manager you will get employee as a child. So it will create a circular data load issue. What is the solution for that? – Tema

this kind of sucks .. you need to introduce a second column just to be able to not have hibernate blow up – Gantt

@SayedUzZaman the solution is to add fetch = FetchType.LAZY in the annotations parameters – Salchunas