I've written the test below and I'm very confussed by the results. It appears that if I make a change to a a hibernated class outside of a transaction and then create a transaction modify a different object and save this object both updates are sent a saved to the database. I would have expected the Address.Address1 property to not get persisted. Is there something wrong with this code or my configuration. This is an issue when we are using the OpenSessionInView model for our ASP.net application, just because an object has changed we don't want to persist it unless saveorUpdate is called explicitly in a transaction for that particular object.

[Test]
public void Test2()
{
Configuration cfg = new Configuration();
cfg.Configure("hibernate.cfg.xml");

ISessionFactory factory = cfg.BuildSessionFactory();
ISession session = factory.OpenSession();
session.FlushMode = FlushMode.Commit;

Address address = session.Load<Address>(3);
address.Address1 = "" + DateTime.Now.ToLongTimeString();

Customer customer = session.Load<Customer>(2);
ITransaction transaction = session.Transaction;
transaction.Begin();
customer.IsActive = false;
session.SaveOrUpdate(customer);
transaction.Commit();
}


hibernate.cfg.xml
<?xml version="1.0" encoding="utf-8" ?>
<hibernate-configuration xmlns="urn:nhibernate-configuration-2.2" >
<session-factory name="NHibernate.Test">
<!-- properties -->
<property name="connection.provider">NHibernate.Connection.DriverConnectionProvider</property>
<property name="connection.driver_class">NHibernate.Driver.SqlClientDriver</property>
<property name="connection.connection_string">Data Source=ssnwserver3;Database=X;User ID=XWebAdmin;Password=XWebAdmin;Min Pool Size=10;Max Pool Size=50;Pooling=true;Connection Lifetime=60;Trusted_Connection=False;</property>
<property name="show_sql">false</property>
<property name="dialect">NHibernate.Dialect.MsSql2005Dialect</property>
<property name="use_outer_join">true</property>
<property name="query.substitutions">true 1, false 0, yes 'Y', no 'N'</property>
<property name="hibernate.cache.use_second_level_cache">false</property>
<property name="hibernate.cache.use_query_cache">false</property>
<property name="hibernate.connection.isolation">Serializable</property>
<property name="show_sql">true</property>
<!-- mapping files -->
<mapping assembly="HibernateTests" />
</session-factory>

</hibernate-configuration>

Actually, transactions don't quite work that way.

Basically, if you have any object attached to a session and it's state changes then those changes will be persisted to the database when a flush occurs.

Normally flushing occurs on an as-needed basis; this could be when you commit a transaction or it could be when you execute a query to ensure that the query results match the data in memory.

You've said explicitly that you only want changes to be flushed on commit of a transaction, but that doesn't mean that changes made to persistent objects outside the transaction won't be tracked - they'll still be flushed when the next flush occurs unless you evict them from the session.

The transaction you've created ensures that all the SQL statements that are executed are all handled in a database transaction. This allows you to make sure that all actions against the database can be atomic for the NHibernate transaction, although the actual database transaction will not start until the first action against the database happens (ie when the first flush occurs).

Does that make sense?

Cheers,

Symon.

Your expectations are wrong. That is indeed how NHibernate works and kind of the whole point - you shouldn't need to tell NHibernate explicitly what to do, it figures it out on its own. Read the documentation.