NHibernate connection driver must be specified in the configuration section

I was in the process of pointing my NHibernate to an Oracle 10g instance using ODP.Net and I received the below error message:

The connection.driver_class must be specified in the NHibernate configuration section.

I had been using a locally installed Microsoft SQL Server database up to that point. It turns out that I needed to add the driver class property to my configuration file.

<property name="connection.driver_class">
     NHibernate.Driver.OracleDataClientDriver
</property>

This interesting thing was that I didn’t have the driver class property configured for my Microsoft SQL Server instance. It worked without it. After the fact I did add it.

<property name="connection.driver_class">
    NHibernate.Driver.SqlClientDriver
</property>

Perhaps because I had the database on my local machine, the Data Source was enough for NHibernate to make the connection. If you know, leave a comment.