hibernate behavior explanation:

hibernate behavior explanation:

I have 3 code snippets:
1:
Session session =
HibernateUtil.getSessionFactory().openSession();
session.beginTransaction();
Prepod prepod = (Prepod) session.load(Prepod.class, 1l);
Student student = (Student) session.load(Student.class, 1l);
Hibernate.initialize(prepod.getStudents());
Hibernate.initialize(student.getPrepods());
session.getTransaction().commit();
session.flush();
session.close();
List<Student> students = new ArrayList<Student>();
students.add(student);
List<Prepod> prepods = new ArrayList<Prepod>();
prepods.add(prepod);
prepod.setStudents(students);
student.setPrepods(prepods);
session = HibernateUtil.getSessionFactory().openSession();
session.beginTransaction();
session.update(student);
session.getTransaction().commit();
session.close();
First snippet works and I saw so log:
Hibernate: select prepod0_.id as id1_1_1_, prepod0_.name as name2_1_1_,
students1_.prepods_id as prepods1_1_3_, student2_.id as students2_2_3_,
student2_.id as id1_0_0_, student2_.age as age2_0_0_, student2_.name as
name3_0_0_ from prepod prepod0_ left outer join prepod_Student students1_
on prepod0_.id=students1_.prepods_id left outer join Student student2_ on
students1_.students_id=student2_.id where prepod0_.id=?
Hibernate: select student0_.id as id1_0_1_, student0_.age as age2_0_1_,
student0_.name as name3_0_1_, prepods1_.students_id as students2_0_3_,
prepod2_.id as prepods1_2_3_, prepod2_.id as id1_1_0_, prepod2_.name as
name2_1_0_ from Student student0_ left outer join prepod_Student prepods1_
on student0_.id=prepods1_.students_id left outer join prepod prepod2_ on
prepods1_.prepods_id=prepod2_.id where student0_.id=?
Hibernate: update Student set age=?, name=? where id=?
2:delete from 1
Hibernate.initialize(prepod.getStudents());
Hibernate.initialize(student.getPrepods());
and we have:
Session session = HibernateUtil.getSessionFactory().openSession();
session.beginTransaction();
Prepod prepod = (Prepod) session.load(Prepod.class, 1l);
Student student = (Student) session.load(Student.class, 1l);
session.getTransaction().commit();
session.flush();
session.close();
List<Student> students = new ArrayList<Student>();
students.add(student);
List<Prepod> prepods = new ArrayList<Prepod>();
prepods.add(prepod);
prepod.setStudents(students);
student.setPrepods(prepods);
session = HibernateUtil.getSessionFactory().openSession();
session.beginTransaction();
session.update(student);
session.getTransaction().commit();
session.close();
result:
Exception in thread "main" org.hibernate.LazyInitializationException:
could not initialize proxy - no Session
at
org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:164)
at
org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:285)
at
org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:185)
at logic.Prepod_$$_javassist_1.setStudents(Prepod_$$_javassist_1.java)
at logic.Main.main(Main.java:43)
3:more delete
session.close();
and
session = HibernateUtil.getSessionFactory().openSession();
Thus we have:
Session session = HibernateUtil.getSessionFactory().openSession();
session.beginTransaction();
Prepod prepod = (Prepod) session.load(Prepod.class, 1l);
Student student = (Student) session.load(Student.class, 1l);
session.getTransaction().commit();
session.flush();
List<Student> students = new ArrayList<Student>();
students.add(student);
List<Prepod> prepods = new ArrayList<Prepod>();
prepods.add(prepod);
prepod.setStudents(students);
student.setPrepods(prepods);
session.beginTransaction();
session.update(student);
session.getTransaction().commit();
session.close();
result of this code: it works and I see so log:
Hibernate: select prepod0_.id as id1_1_1_, prepod0_.name as name2_1_1_,
students1_.prepods_id as prepods1_1_3_, student2_.id as students2_2_3_,
student2_.id as id1_0_0_, student2_.age as age2_0_0_, student2_.name as
name3_0_0_ from prepod prepod0_ left outer join prepod_Student students1_
on prepod0_.id=students1_.prepods_id left outer join Student student2_ on
students1_.students_id=student2_.id where prepod0_.id=?
Hibernate: select student0_.id as id1_0_1_, student0_.age as age2_0_1_,
student0_.name as name3_0_1_, prepods1_.students_id as students2_0_3_,
prepod2_.id as prepods1_2_3_, prepod2_.id as id1_1_0_, prepod2_.name as
name2_1_0_ from Student student0_ left outer join prepod_Student prepods1_
on student0_.id=prepods1_.students_id left outer join prepod prepod2_ on
prepods1_.prepods_id=prepod2_.id where student0_.id=?
Hibernate: insert into prepod_Student (prepods_id, students_id) values (?, ?)
Especially note for this line:
Hibernate: insert into prepod_Student (prepods_id, students_id) values (?, ?)
This behavior doesn't understand for me. Can you explain me why I saw
these results?