this is the error when i load product entity

my code is

 Configuration cfg = new NHibernate.Cfg.Configuration();
        ISessionFactory sessions;

        public MedicineController() //Construtor
        {
            cfg.Configure();
            sessions = cfg.BuildSessionFactory();
        }

using (var session = sessions.OpenSession())
            {
                var pGet = session.Get<Product>(0);
            }

The Error is

Unable to locate persister for the entity named 'SharpArchitecture.Domain.Product'. The persister define the persistence strategy for an entity. Possible causes: - The mapping for 'SharpArchitecture.Domain.Product' was not added to the NHibernate configuration.

Thanks in advance