I mapped some classes to some tables with hibernate in java, i set hibernate to show SQL, it opens the session, it show that id does the SQL, it closes the session but there are no modifications to the database.

Entity

public class Profesor implements Comparable<Profesor> {
private int id;
private String nume;
private String prenume;
private int departament_id;
private Set<Disciplina> listaDiscipline; //the teacher gives some courses}

public class Disciplina implements Comparable<Disciplina>{ //the course class

private int id;
private String denumire;
private String syllabus;
private String schNotare;
private Set<Lectie> lectii;
private Set<Tema> listaTeme;
private Set<Grup> listaGrupuri; // the course gets teached/assigmened to some groups of students
private Set<Assignment> listAssignments;}

Mapping

<hibernate-mapping default-cascade="all">
<class name="model.Profesor" table="devgar_scoala.profesori">
<id name="id" column="id">
 <generator class="increment"/>
</id>
<set name="listaDiscipline" table="devgar_scoala.`profesori-discipline`">
<key column="Profesori_id" />
<many-to-many class="model.Disciplina" column="Discipline_id"  />
</set>
<property name="nume" column="Nume" type="string" />
<property name="prenume" column="Prenume" type="string" />
<property name="departament_id" column="Departamente_id" type="integer" />
</class>

<class name="model.Grup" table="devgar_scoala.grupe">
<id name="id" unsaved-value="0">
<generator class="increment"/>
</id>
<set name="listaStudenti" table="devgar_scoala.`studenti-grupe`">
<key column="Grupe_id" />
<many-to-many column="Studenti_nrMatricol" class="model.Student" />
</set>

<property name="nume" column="Grupa" type="string"/>
<property name="programStudiu" column="progStudii_id" type="integer" />
</class>
<class name="model.Disciplina" table="devgar_scoala.discipline" >
<id name="id"  >
<generator class="increment"/>
</id> 
<property name="denumire" column="Denumire" type="string"/>
<property name="syllabus" type="string" column="Syllabus"/>
<property name="schNotare" type="string" column="SchemaNotare"/>

<set name="listaGrupuri" table="devgar_scoala.`Discipline-Grupe`">
<key column="Discipline_id" />
<many-to-many column="Grupe_id" class="model.Grup" />
</set>

<set name="lectii" table="devgar_scoala.lectii">
<key column="Discipline_id" not-null="true"/>
<one-to-many class="model.Lectie"  />
</set>
</class>

The only 'funny' thing is that the Profesor object gets loaded not with/by Hibernate but with manual classic SQL Java. Thats why i save the Profesor object like this p - the manually loaded Profesor object

Profesor p2 = (Profesor) session.merge(p);
session.saveOrUpdate(p2);


//flush session of course

After this i get in the Java console:

Hibernate: insert into devgar_scoala.grupe (Grupa, progStudii_id, id) values (?, ?, ?)

but when i look into the database there are no new rows in the table Grupe (the Groups table)