spring jpa add field to many to many table

@Entity
public class Employer {

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

    @OneToMany(mappedBy = "employer")
    private List<EmployerDeliveryAgent> deliveryAgentAssoc;

    // other properties and getters and setters
}

@Entity
public class DeliveryAgent {

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

    @OneToMany(mappedBy = "deliveryAgent")
    private List<EmployerDeliveryAgent> employerAssoc;

    // other properties and getters and setters
}

@Entity
@Table(name = "employer_delivery_agent")
@IdClass(EmployerDeliveryAgentId.class)
public class EmployerDeliveryAgent {

    @Id
    @ManyToOne
    @JoinColumn(name = "employer_id", referencedColumnName = "id")
    private Employer employer;

    @Id
    @ManyToOne
    @JoinColumn(name = "delivery_agent_id", referencedColumnName = "id")
    private DeliveryAgent deliveryAgent;

    @Column(name = "is_project_lead")
    private boolean isProjectLead;
}

public class EmployerDeliveryAgentId implements Serializable {

    private int employer;
    private int deliveryAgent;

    // getters/setters and most importantly equals() and hashCode()
}