public static VerticalLayout formonetomany(VerticalLayout layout) {
        // Populate with example data
        // JPAContainerExample.insertExampleData();

        // BEGIN-EXAMPLE: jpacontainer.fieldfactory.formonetoone
        // Have a persistent container
        final JPAContainer<Country> countries =
                JPAContainerFactory.make(Country.class, "VaadinJPAUnderstandingPU");

        // For selecting an item to edit
        final Select countrySelect = new Select("Select a Country", countries);
        countrySelect.setItemCaptionMode(Select.ITEM_CAPTION_MODE_PROPERTY);
        countrySelect.setItemCaptionPropertyId("name");

        // Country Editor
        final Form countryForm = new Form();
        countryForm.setCaption("Country Editor");
        countryForm.addStyleName("bordered"); // Custom style
        countryForm.setWidth("420px");
        countryForm.setWriteThrough(false); // Enable buffering
        countryForm.setEnabled(false);

        // When an item is selected from the list...
        countrySelect.addListener(new ValueChangeListener() {

            private static final long serialVersionUID = 3371750143781493244L;

            @Override
            public void valueChange(ValueChangeEvent event) {
                // Get the item to edit in the form
                Item countryItem =
                        countries.getItem(event.getProperty().getValue());

                // Use a JPAContainer field factory
                //  - no configuration is needed here
                final FieldFactory fieldFactory = new FieldFactory();
                countryForm.setFormFieldFactory(fieldFactory);

                // Edit the item in the form
                countryForm.setItemDataSource(countryItem);
                countryForm.setEnabled(true);

                // Handle saves on the form
                final Button save = new Button("Save");
                countryForm.getFooter().removeAllComponents();
                countryForm.getFooter().addComponent(save);
                save.addListener(new ClickListener() {

                    private static final long serialVersionUID = 3147385792741616617L;

                    @Override
                    public void buttonClick(ClickEvent event) {
                        try {
                            countryForm.commit();
                            countryForm.setEnabled(false);
                        } catch (InvalidValueException e) {
                        }
                    }
                });
            }
        });
        countrySelect.setImmediate(true);
        countrySelect.setNullSelectionAllowed(false);
        // END-EXAMPLE: jpacontainer.fieldfactory.formonetoone

        layout.setSpacing(true);
        layout.addComponent(countrySelect);
        layout.addComponent(countryForm);
        return layout;
    }

@Entity
public class Person implements Serializable {
    private static final long serialVersionUID = 508426585088564210L;
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long    id;

    private String  name;
    private Integer age;

    @ManyToOne
    private Country country;

    /** Default constructor is required by JPA */
    public Person() {
    }

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

    public Person(String name, int age, Country country) {
        this.name    = name;
        this.age     = age;
        this.country = country;
        country.addPerson(this);
    }

    public Long getId() {
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Integer getAge() {
        return age;
    }
    public void setAge(Integer age) {
        this.age = age;
    }
    public Country getCountry() {
        return country;
    }
    public void setCountry(Country country) {
        this.country = country;
        country.addPerson(this);
    }
}

@Entity
public class Country implements Serializable {

    private static final long serialVersionUID = 508426585088564210L;
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    @OneToMany(mappedBy = "country", cascade = CascadeType.ALL, orphanRemoval = true,fetch=FetchType.LAZY)
    private Set<Person> people;

    /** Default constructor is required by JPA */
    public Country() {
        people = new HashSet<Person>();
    }

    public Country(String name) {
        this.name = name;
        this.people = new HashSet<Person>();
    }

    /** Adds a person to the country. */
    public void addPerson(Person person) {
        people.add(person);
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

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

    public Set<Person> getPeople() {
        return people;
    }

    public void setPeople(Set<Person> people) {
        this.people = people;
    }
}
// END-EXAMPLE: jpacontainer.basic