First you should download the Oracle Data Provider for .NET in
http://www.oracle.com/technology/tech/windows/odpnet/index.html
after you make sure that you can open a connection to your oracle database then
define mapping file of your entities in Nhibernate and map table columns of your oracle table to .NET object. after that you can use the following code snippet to get the list of your entity from database
// create the query...
IQuery query = session.CreateQuery( "from Post p where p.Blog.Author = :author" );
// set the parameters...
query.SetString("author", (String) instance);
// fetch the results...
IList results = query.List();
You should define the (Post) entity and (Blog) entity to your mapping file and as you can see (Post) has relation to (Blog) entity which is defined in the mapping file too.