/**

     * Save the analysis to the DB, first cleaning up any old ones.

     *

     * @param \qubaid_condition $qubaids    which question usages have been analysed.

     * @param string            $whichtries which tries have been analysed?

     * @param int               $questionid which question.

     * @param int|null          $calculationtime time when the analysis was done. (Defaults to time()).

     */

    public function cache($qubaids, $whichtries, $questionid, $calculationtime = null) {

        global $DB;

        $transaction = $DB->start_delegated_transaction();

        // Delete in chunks for better performance on InnoDB

        // https://git.arnes.si/ucilnice/moodle/-/issues/12

        $allids = $DB->get_records_sql_menu("

                SELECT DISTINCT id, id AS id2

                  FROM {question_response_analysis}

                WHERE hashcode = ? AND whichtries = ? AND questionid = ?",

                [$qubaids->get_hash_code(), $whichtries, $questionid]

        );

        foreach (array_chunk($allids, 10000) as $todelete) {

            list($idsql, $idparams) = $DB->get_in_or_equal($todelete);

            $DB->execute('

                    DELETE FROM {question_response_count}

                     WHERE id ' . $idsql,

                     $idparams

            );

            $DB->execute('

                    DELETE FROM {question_response_analysis}

                     WHERE id ' . $idsql,

                     $idparams

             );

        }

        foreach ($this->get_variant_nos() as $variantno) {

            foreach ($this->get_subpart_ids($variantno) as $subpartid) {

                $analysisforsubpart = $this->get_analysis_for_subpart($variantno, $subpartid);

                $analysisforsubpart->cache($qubaids, $whichtries, $questionid, $variantno, $subpartid, $calculationtime);

            }

        }

        $transaction->allow_commit();

    }