An item with the same key has already been added.

Question

Can someone advice me how to prevent this error. An item with the same key has already been added.?

//  Failed to find a matching SessionFactory so make a new one.
        if (sessionFactory == null)
        {
            Check.Require(File.Exists(sessionFactoryConfigPath),
                          "The config file at '" + sessionFactoryConfigPath + "' could not be found");

            Configuration cfg = new Configuration();
            cfg.Configure(sessionFactoryConfigPath);

            /*MINE*/
            var persistenceModel = new PersistenceModel();
            persistenceModel.AddMappingsFromAssembly(Assembly.Load("EMedicine.Core"));
            persistenceModel.Configure(cfg);
            /*END_OF_MINE*/

            //  Now that we have our Configuration object, create a new SessionFactory
            sessionFactory = cfg.BuildSessionFactory();

            if (sessionFactory == null)
            {
                throw new InvalidOperationException("cfg.BuildSessionFactory() returned null.");
            }

            if (sessionFactoryConfigPath != null) sessionFactories.Add(sessionFactoryConfigPath, sessionFactory);
        }

Error is here: sessionFactory = cfg.BuildSessionFactory();

Answer 1

Try the following:

if (
    sessionFactoryConfigPath != null && 
    sessionFactories.ContainsKey(sessionFactoryConfigPath)
) {
    sessionFactory = cfg.BuildSessionFactory();

    if (sessionFactory == null)
    {
        throw new InvalidOperationException("cfg.BuildSessionFactory() returned null.");
    }

    sessionFactories.Add(sessionFactoryConfigPath, sessionFactory);
} else (sessionFactoryConfigPath != null) {
    sessionFactory = sessionFactories[sessionFactoryConfigPath];
}

Answer 2

Is this solution OK?

try { // Now that we have our Configuration object, create a new SessionFactory sessionFactory = cfg.BuildSessionFactory();

                    if (sessionFactory == null)
                    {
                        throw new InvalidOperationException("cfg.BuildSessionFactory() returned null.");
                    }

                    if (sessionFactoryConfigPath != null)
                        sessionFactories.Add(sessionFactoryConfigPath, sessionFactory);
                }
                catch (Exception)
                { 
                    if (sessionFactoryConfigPath != null)
                        sessionFactory = (ISessionFactory) sessionFactories[sessionFactoryConfigPath];
                }