I have set the id like this:
<id name="UserId"
column="UserId"
type="System.String">
<generator class="assigned"/>
</id>

Then when I save the entity:
session.openSession();
session.save(entity);

But unfortunately, nothing has happend. No record is inserted into the database.

So what do I miss?

Thank you very much

Using session.Save(obj) you only save the object to the NHibernate cache. To store your object into the database, you have to call session.Flush() after session.Save(obj).

You can also use transactions. Then it ist not necessary to call Flush() explicitly.

ITransaction tx = session.BeginTransaction();
session.Save(obj);
tx.Commit();

Yes, it works.
Thanks