Hi,
I'm actually develloping an application using a tomcat webserver, hibernate and multiple mysql databases on differents computers.
I use actually MySQL Connector/J to link one of these database to my web application but as MySQL Connector/J will at the end link others database I was wondering if hibernate will be able to switch from one database to another ? (in sql i just would have to specify manually the database used like this : SELECT dbname.tablename.colname FROM dbname.tablename... but with hibernate xml parsing and HQL ?)

In clear does hibernate support a multiple database architecture ?

create a new session factory for each database and use the appropriate session (conection) while accessing/creating objects.

the curent design pattern is aimed towards one datasource per database

of course you can't expect associations between objects from different databses to work.

so you mean that I must put more than one session factory in my hibernate.cfg.xml file ?
Ok with that but how will i then specify the database to use when i create my factory object in my javacode ?
here here is my factory in the xml file :

public void init(FilterConfig filterConfig) throws ServletException

<session-factory>
<property name="connection.datasource">java:comp/env/jdbc/projet2</property>
<property name="show_sql">false</property>
<property name="dialect">net.sf.hibernate.dialect.MySQLDialect</property>
<!-- Mapping files -->
<mapping resource="data/DataSet.hbm.xml"/>
<mapping resource="data/Measure.hbm.xml"/>
<mapping resource="data/Parameter.hbm.xml"/>
</session-factory>

and is the java code i use to initialize my factory :

{
// Initialize hibernate
try
{
factory = new Configuration().configure().buildSessionFactory();
}
catch (HibernateException ex) { throw new ServletException(ex); }
}

If these are just different mysql databases on the same physical server, you can also play with the schema attribute in the mappings. Probably you need to create your own dialect overriding getSchemaSeperator()

regardless of how you choose to configure the factory note that it results in a single Confugration object to be created.

in your case there needs to be on cfg.xml for per factory. i prefer to do this programatically (for e.g. having a separate startup bean for each factory).

since you say you have the databases on separate servers, you can init all the connections from a single app server

Wow great !
thanks very much :)

Sorry to bother you again but I still don't see what you mean by use the appropriate session where in my java code will I have to specify the database in use and how ^^;
another thing is : How can I have more than one hibernate.cfg.xml ? isn't this file supposed to be placed in the root on my classes diectory ?

Create two Configuration objects with two hibernate.cfg.xml, build two SessionFactories from those Configurations, get Sessions from each. You can't link database that way, only use them.