Re: hibernate question ?

I have an entity like
@Entity
public class Address {
    @Id
    private int id;
    private String street;
    private String city;
    private String state;
    private String zip;
    private Set<Address> addressSet = new HashSet<Address>();

    public int getId() {
        return id;
    }

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

...

    @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY,
        mappedBy = "address")
    public Set<Address> getAddressSet() {
        return this.addressSet;
    }

    public void setAuthDevices(Set<Address> address) {
        this.addressSet = address;
    }
}

and entity :

@Entity
public class Student {
    @Id
    private int id;
    private String name;

    @ManyToOne(cascade=CascadeType.PERSIST)
    Address address;

    public int getId() {
        return id;
    }

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

...
}

if i [sic] do this :

Student emp = new Student();
    emp.setId(1);
    emp.setName("name");
    Address addr = new Address();
    addr.setId(1);
    addr.setStreet("street");
    addr.setCity("city");
    addr.setState("state");
    emp.setAddress(addr);
    addr.getAddressSet().add(emp);
    em.persist(emp);

the cascade attribute works and two insert are generated(cascade persist
works, but whenI do something like this :

    Student emp = em.find(Student.class, 1L);
    emp.setName("name");
    Address addr = em.find(Adress.class, 1L);
    addr.setStreet("streetOne");
    emp.setAddress(addr);
    em.persist(emp);

two sql updates are generates and address and student is updates, but
there is NO cascade = MERGE on Student entity... how is this POSSIBLE ?