How to extract field value from another field that is of type Object

I'm new to java reflexion and I'm trying to integrate SQLite with java.

I have 2 objects Person and Department. There is relation OneToMany between them.

As I'm working on save functionality (SQLite) I want to extract field names and its values so I can build full query. I have no problem with extracting names and values of fields that are of primitive type (String, int etc.). I have problem with type of Object (in this case it is Department field in Person object).

I'm able to print object but unable to access its fields (namely pk).

Could you help me please?

METHOD FOR EXTRACTING FIELDS

// method for extracting fields
private StringBuilder getFieldsWithValues(Object entity) throws IllegalAccessException, NoSuchFieldException {
        StringBuilder query = new StringBuilder();

        for (Field field : entity.getClass().getDeclaredFields()) {
            System.out.print((field.getName() + " - "));
            field.setAccessible(true);
            // TODO: eliminate if statement from for cycle
            if (field.isAnnotationPresent(ManyToOne.class)) {
                // HERE I want to extract the pk value from Department object
                System.out.println(field.get(entity));
            } else {
                System.out.println(field.get(entity));
            }
        }
        return query;
    } 

DEPARTMENT OBJECT

import javax.persistence.Entity;
import javax.persistence.Id;

@Entity
public class Department {
    @Id
    private long pk;
    private String name;
    private String code;

    public Department() {
    }

    public Department(String name, String code) {
        this.name = name;
        this.code = code;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getCode() {
        return code;
    }

    public void setCode(String code) {
        this.code = code;
    }

    public String toString() {
        return String.format("Department %d: %s (%s)", pk, name, code);
    }
} 

PERSON OBJECT

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.ManyToOne;

@Entity
public class Person {
    @Id
    private long id;
    private String surname;
    private String name;
    private int age;

    @ManyToOne
    private Department department;

    public Person(String surname, String name, int age) {
        this.surname = surname;
        this.name = name;
        this.age = age;
    }

    public Person() {
    }

    public String getSurname() {
        return surname;
    }

    public void setSurname(String surname) {
        this.surname = surname;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public long getId() {
        return id;
    }


    public Department getDepartment() {
        return department;
    }

    public void setDepartment(Department department) {
        this.department = department;
    }

    @Override
    public String toString() {
        return String.format("Person %d: %s %s (%d)", id, surname, name, age);
    }
}