a method to determine if record exists
            
        :param primary_key: string with primary key of record 
        :return: boolean to indicate existence of record

def exists(self, primary_key):
        
        '''
            a method to determine if record exists
            
        :param primary_key: string with primary key of record 
        :return: boolean to indicate existence of record
        '''
        
        select_statement = self.table.select(self.table).where(self.table.c.id==primary_key)
        record_object = self.session.execute(select_statement).first()
        if record_object:
            return True
        return False