Add the given primary text to the cache database, updating
        the existing record if the primary text is already present

        :type item_url: String or Item
        :param item_url: the URL of the corresponding item, or an Item object
        :type primary_text: String
        :param primary_text: the item's primary text

def add_primary_text(self, item_url, primary_text):
        """ Add the given primary text to the cache database, updating
        the existing record if the primary text is already present

        :type item_url: String or Item
        :param item_url: the URL of the corresponding item, or an Item object
        :type primary_text: String
        :param primary_text: the item's primary text


        """
        c = self.conn.cursor()
        c.execute("DELETE FROM primary_texts WHERE item_url=?",
                      (str(item_url),))
        self.conn.commit()
        c.execute("INSERT INTO primary_texts VALUES (?, ?, ?)",
                  (str(item_url), primary_text, self.__now_iso_8601()))
        self.conn.commit()
        c.close()