public static string OraCode { get; set; }
public static string OraMessage { get; set; }

// изменение сущности 'Author'
public static void AuthorMod(Author a, ISession session)
{
    ITransaction transaction = null;
    try
    {
        // execute stored procedure
        OracleCommand command = session.Connection.CreateCommand() as OracleCommand;

        transaction = session.BeginTransaction();
        transaction.Enlist(command);

        command.CommandType = CommandType.StoredProcedure;
        command.CommandText = "PKG_AUTHORS.AUTHOR_MOD";

        OracleParameter p = command.Parameters.AddWithValue("pId", a.Id);
        p = command.Parameters.AddWithValue("pName", a.Name);

        p = command.Parameters.Add("pErrCode", OracleType.VarChar);
        p.Direction = ParameterDirection.Output;
        p.Size = sizeof(char) * 8096;
        p = command.Parameters.Add("pErrMsg", OracleType.VarChar);
        p.Direction = ParameterDirection.Output;
        p.Size = sizeof(char) * 8096;

        int ret = command.ExecuteNonQuery();
        transaction.Commit();

        // save possible Oracle error
        OraCode = command.Parameters[2].Value as string;
        OraMessage = command.Parameters[3].Value as string;
    }
    catch (Exception e)
    {
        if (transaction != null && transaction.IsActive)
            transaction.Rollback();
        throw;
    }
}

transaction = session.BeginTransaction();
transaction.Enlist(command);