Hibernate version:
2.1

Mapping documents:
<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration
PUBLIC "-//Hibernate/Hibernate Configuration DTD//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-2.0.dtd">

<hibernate-configuration>
<session-factory>
<!-- properties -->
<property name = "hibernate.show_sql">false</property>

<property name = "hibernate.hbm2ddl.auto">update</property>

<!-- mapping files -->
<mapping resource = "escola/Relatorio.hbm.xml"/>
<mapping resource = "escola/Acessorios.hbm.xml"/>
<mapping resource = "escola/Turma.hbm.xml"/>
<mapping resource = "escola/EducacaoArtistica.hbm.xml"/>
<mapping resource = "escola/EducacaoFisica.hbm.xml"/>
<mapping resource = "escola/EducacaoMoralEReligiosa.hbm.xml"/>
<mapping resource = "escola/EducacaoMusical.hbm.xml"/>
<mapping resource = "escola/EducacaoTecnologica.hbm.xml"/>
<mapping resource = "escola/EducacaoVisualETecnologica.hbm.xml"/>
<mapping resource = "escola/EstudoDoMeio.hbm.xml"/>
<mapping resource = "escola/ExpressaoArtistica.hbm.xml"/>
<mapping resource = "escola/Matematica.hbm.xml"/>
<mapping resource = "escola/LinguaPortuguesa.hbm.xml"/>
<mapping resource = "escola/LEI.hbm.xml"/>
<mapping resource = "escola/Q9.hbm.xml"/>
<mapping resource = "escola/Q10.hbm.xml"/>
<mapping resource = "escola/Q12.hbm.xml"/>
<mapping resource = "escola/Q17.hbm.xml"/>
<mapping resource = "escola/Q19.hbm.xml"/>
<mapping resource = "escola/Q22Al.hbm.xml"/>
<mapping resource = "escola/Q22Disc.hbm.xml"/>
<mapping resource = "escola/Q22EE.hbm.xml"/>
<mapping resource = "escola/Q22Esc.hbm.xml"/>
<mapping resource = "escola/Q23.hbm.xml"/>
<mapping resource = "escola/Q34.hbm.xml"/>
<mapping resource = "escola/Utilizador.hbm.xml"/>
</session-factory>
</hibernate-configuration>


Code between sessionFactory.openSession() and session.close():

Full stack trace of any exception that occurs:

Name and version of the database you are using:
MySql 4.0.12-nt

Debug level Hibernate log excerpt:

I read in manual's ch 3.5 that we can use hibernate.hbm2ddl.auto with update, which i adopted:
<property name = "hibernate.hbm2ddl.auto">update</property>
This is great because i can have data in database and at the same time update it without any loss of data.
But i watched this:

...
19:33:03,375 DEBUG SchemaUpdate:133 - alter table q22Al add index (matematica_id), add constraint FK64FDE7C7F49A5CE foreign key (matematica_id) references matematica (id)
...
I mean, the database update creates a constraint: i wonder if i should worry about that, if that, in any way, may affect my data and the overall natural flow of my app
Thanks in advance

Automatic database schema update _may_ be useful in development, but never in production or with anything else that involves important data. It's just too fragile and depends on too many variables.

I see
My idea is that i'm making this app by stages, and only on second stage i'd add more objs, but then i'de to expand database mannually, acording to what you recomend...