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322 lines
14 KiB
322 lines
14 KiB
<?php
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// This file is part of Moodle - http://moodle.org/
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//
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// Moodle is free software: you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// Moodle is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with Moodle. If not, see <http://www.gnu.org/licenses/>.
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/**
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* A class for efficiently finds questions at random from the question bank.
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*
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* @package core_question
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* @copyright 2015 The Open University
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* @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
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*/
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namespace core_question\bank;
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/**
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* This class efficiently finds questions at random from the question bank.
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*
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* You can ask for questions at random one at a time. Each time you ask, you
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* pass a category id, and whether to pick from that category and all subcategories
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* or just that category.
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*
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* The number of teams each question has been used is tracked, and we will always
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* return a question from among those elegible that has been used the fewest times.
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* So, if there are questions that have not been used yet in the category asked for,
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* one of those will be returned. However, within one instantiation of this class,
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* we will never return a given question more than once, and we will never return
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* questions passed into the constructor as $usedquestions.
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*
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* @copyright 2015 The Open University
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* @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
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*/
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class random_question_loader {
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/** @var \qubaid_condition which usages to consider previous attempts from. */
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protected $qubaids;
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/** @var array qtypes that cannot be used by random questions. */
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protected $excludedqtypes;
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/** @var array categoryid & include subcategories => num previous uses => questionid => 1. */
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protected $availablequestionscache = array();
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/**
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* @var array questionid => num recent uses. Questions that have been used,
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* but that is not yet recorded in the DB.
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*/
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protected $recentlyusedquestions;
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/**
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* Constructor.
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* @param \qubaid_condition $qubaids the usages to consider when counting previous uses of each question.
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* @param array $usedquestions questionid => number of times used count. If we should allow for
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* further existing uses of a question in addition to the ones in $qubaids.
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*/
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public function __construct(\qubaid_condition $qubaids, array $usedquestions = array()) {
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$this->qubaids = $qubaids;
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$this->recentlyusedquestions = $usedquestions;
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foreach (\question_bank::get_all_qtypes() as $qtype) {
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if (!$qtype->is_usable_by_random()) {
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$this->excludedqtypes[] = $qtype->name();
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}
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}
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}
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/**
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* Pick a question at random from the given category, from among those with the fewest uses.
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* If an array of tag ids are specified, then only the questions that are tagged with ALL those tags will be selected.
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*
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* It is up the the caller to verify that the cateogry exists. An unknown category
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* behaves like an empty one.
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*
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* @param int $categoryid the id of a category in the question bank.
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* @param bool $includesubcategories wether to pick a question from exactly
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* that category, or that category and subcategories.
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* @param array $tagids An array of tag ids. A question has to be tagged with all the provided tagids (if any)
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* in order to be eligible for being picked.
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* @return int|null the id of the question picked, or null if there aren't any.
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*/
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public function get_next_question_id($categoryid, $includesubcategories, $tagids = []) {
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$this->ensure_questions_for_category_loaded($categoryid, $includesubcategories, $tagids);
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$categorykey = $this->get_category_key($categoryid, $includesubcategories, $tagids);
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if (empty($this->availablequestionscache[$categorykey])) {
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return null;
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}
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reset($this->availablequestionscache[$categorykey]);
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$lowestcount = key($this->availablequestionscache[$categorykey]);
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reset($this->availablequestionscache[$categorykey][$lowestcount]);
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$questionid = key($this->availablequestionscache[$categorykey][$lowestcount]);
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$this->use_question($questionid);
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return $questionid;
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}
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/**
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* Get the key into {@link $availablequestionscache} for this combination of options.
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* @param int $categoryid the id of a category in the question bank.
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* @param bool $includesubcategories wether to pick a question from exactly
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* that category, or that category and subcategories.
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* @param array $tagids an array of tag ids.
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* @return string the cache key.
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*/
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protected function get_category_key($categoryid, $includesubcategories, $tagids = []) {
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if ($includesubcategories) {
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$key = $categoryid . '|1';
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} else {
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$key = $categoryid . '|0';
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}
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if (!empty($tagids)) {
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$key .= '|' . implode('|', $tagids);
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}
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return $key;
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}
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/**
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* Populate {@link $availablequestionscache} for this combination of options.
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* @param int $categoryid The id of a category in the question bank.
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* @param bool $includesubcategories Whether to pick a question from exactly
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* that category, or that category and subcategories.
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* @param array $tagids An array of tag ids. If an array is provided, then
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* only the questions that are tagged with ALL the provided tagids will be loaded.
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*/
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protected function ensure_questions_for_category_loaded($categoryid, $includesubcategories, $tagids = []) {
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global $DB;
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$categorykey = $this->get_category_key($categoryid, $includesubcategories, $tagids);
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if (isset($this->availablequestionscache[$categorykey])) {
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// Data is already in the cache, nothing to do.
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return;
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}
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// Load the available questions from the question bank.
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if ($includesubcategories) {
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$categoryids = question_categorylist($categoryid);
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} else {
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$categoryids = array($categoryid);
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}
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list($extraconditions, $extraparams) = $DB->get_in_or_equal($this->excludedqtypes,
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SQL_PARAMS_NAMED, 'excludedqtype', false);
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$questionidsandcounts = \question_bank::get_finder()->get_questions_from_categories_and_tags_with_usage_counts(
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$categoryids, $this->qubaids, 'q.qtype ' . $extraconditions, $extraparams, $tagids);
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if (!$questionidsandcounts) {
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// No questions in this category.
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$this->availablequestionscache[$categorykey] = array();
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return;
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}
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// Put all the questions with each value of $prevusecount in separate arrays.
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$idsbyusecount = array();
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foreach ($questionidsandcounts as $questionid => $prevusecount) {
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if (isset($this->recentlyusedquestions[$questionid])) {
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// Recently used questions are never returned.
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continue;
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}
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$idsbyusecount[$prevusecount][] = $questionid;
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}
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// Now put that data into our cache. For each count, we need to shuffle
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// questionids, and make those the keys of an array.
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$this->availablequestionscache[$categorykey] = array();
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foreach ($idsbyusecount as $prevusecount => $questionids) {
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shuffle($questionids);
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$this->availablequestionscache[$categorykey][$prevusecount] = array_combine(
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$questionids, array_fill(0, count($questionids), 1));
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}
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ksort($this->availablequestionscache[$categorykey]);
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}
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/**
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* Update the internal data structures to indicate that a given question has
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* been used one more time.
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*
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* @param int $questionid the question that is being used.
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*/
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protected function use_question($questionid) {
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if (isset($this->recentlyusedquestions[$questionid])) {
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$this->recentlyusedquestions[$questionid] += 1;
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} else {
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$this->recentlyusedquestions[$questionid] = 1;
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}
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foreach ($this->availablequestionscache as $categorykey => $questionsforcategory) {
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foreach ($questionsforcategory as $numuses => $questionids) {
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if (!isset($questionids[$questionid])) {
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continue;
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}
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unset($this->availablequestionscache[$categorykey][$numuses][$questionid]);
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if (empty($this->availablequestionscache[$categorykey][$numuses])) {
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unset($this->availablequestionscache[$categorykey][$numuses]);
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}
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}
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}
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}
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/**
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* Get the list of available question ids for the given criteria.
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*
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* @param int $categoryid The id of a category in the question bank.
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* @param bool $includesubcategories Whether to pick a question from exactly
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* that category, or that category and subcategories.
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* @param array $tagids An array of tag ids. If an array is provided, then
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* only the questions that are tagged with ALL the provided tagids will be loaded.
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* @return int[] The list of question ids
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*/
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protected function get_question_ids($categoryid, $includesubcategories, $tagids = []) {
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$this->ensure_questions_for_category_loaded($categoryid, $includesubcategories, $tagids);
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$categorykey = $this->get_category_key($categoryid, $includesubcategories, $tagids);
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$cachedvalues = $this->availablequestionscache[$categorykey];
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$questionids = [];
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foreach ($cachedvalues as $usecount => $ids) {
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$questionids = array_merge($questionids, array_keys($ids));
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}
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return $questionids;
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}
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/**
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* Check whether a given question is available in a given category. If so, mark it used.
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* If an optional list of tag ids are provided, then the question must be tagged with
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* ALL of the provided tags to be considered as available.
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*
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* @param int $categoryid the id of a category in the question bank.
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* @param bool $includesubcategories wether to pick a question from exactly
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* that category, or that category and subcategories.
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* @param int $questionid the question that is being used.
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* @param array $tagids An array of tag ids. Only the questions that are tagged with all the provided tagids can be available.
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* @return bool whether the question is available in the requested category.
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*/
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public function is_question_available($categoryid, $includesubcategories, $questionid, $tagids = []) {
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$this->ensure_questions_for_category_loaded($categoryid, $includesubcategories, $tagids);
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$categorykey = $this->get_category_key($categoryid, $includesubcategories, $tagids);
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foreach ($this->availablequestionscache[$categorykey] as $questionids) {
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if (isset($questionids[$questionid])) {
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$this->use_question($questionid);
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return true;
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}
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}
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return false;
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}
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/**
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* Get the list of available questions for the given criteria.
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*
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* @param int $categoryid The id of a category in the question bank.
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* @param bool $includesubcategories Whether to pick a question from exactly
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* that category, or that category and subcategories.
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* @param array $tagids An array of tag ids. If an array is provided, then
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* only the questions that are tagged with ALL the provided tagids will be loaded.
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* @param int $limit Maximum number of results to return.
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* @param int $offset Number of items to skip from the begging of the result set.
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* @param string[] $fields The fields to return for each question.
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* @return \stdClass[] The list of question records
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*/
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public function get_questions(
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$categoryid,
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$includesubcategories,
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$tagids = [],
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$limit = 100,
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$offset = 0,
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$fields = []
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) {
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global $DB;
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$questionids = $this->get_question_ids($categoryid, $includesubcategories, $tagids);
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if (empty($questionids)) {
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return [];
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}
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if (empty($fields)) {
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// Return all fields.
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$fieldsstring = '*';
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} else {
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$fieldsstring = implode(',', $fields);
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}
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return $DB->get_records_list(
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'question',
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'id',
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$questionids,
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'id',
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$fieldsstring,
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$offset,
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$limit
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);
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}
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/**
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* Count the number of available questions for the given criteria.
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*
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* @param int $categoryid The id of a category in the question bank.
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* @param bool $includesubcategories Whether to pick a question from exactly
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* that category, or that category and subcategories.
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* @param array $tagids An array of tag ids. If an array is provided, then
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* only the questions that are tagged with ALL the provided tagids will be loaded.
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* @return int The number of questions matching the criteria.
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*/
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public function count_questions($categoryid, $includesubcategories, $tagids = []) {
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$questionids = $this->get_question_ids($categoryid, $includesubcategories, $tagids);
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return count($questionids);
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}
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}
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