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<?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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 * Generic temptables object store
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 *
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 * Provides support to databases lacking some "expected behaviour" related
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 * with some operations with temporary tables like:
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 *
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 *   - databases not retrieving temp tables from information schema tables (mysql)
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 *   - databases using a different name schema for temp tables (like mssql).
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 *   - databases that don't collect planner stats for temp tables (like PgSQL).
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 *
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 * Basically it works as a simple store of created temporary tables, providing
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 * some simple getters/setters methods. Each database can extend it for its own
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 * purposes (for example, return correct name, see the mssql implementation)
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 *
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 * The unique instance of the object by database connection is shared by the database
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 * and the sql_generator, so both are able to use its facilities, with the final goal
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 * of doing temporary tables support 100% cross-db and transparent within the DB API.
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 *
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 * @package    core_dml
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 * @copyright  2009 onwards Eloy Lafuente (stronk7) {@link http://stronk7.com}
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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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defined('MOODLE_INTERNAL') || die();
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class moodle_temptables {
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    /** @var circular reference, to be able to use DB facilities here if needed */
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    protected $mdb;
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    /** @var prefix to be used for all the DB objects */
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    protected $prefix;
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    /** @var simple array of moodle, not prefixed 'tablename' => DB, final (prefixed) 'tablename' */
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    protected $temptables;
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    /**
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     * Creates new moodle_temptables instance
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     * @param moodle_database $mdb An instance of moodle_database.
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     */
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    public function __construct($mdb) {
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        $this->mdb        = $mdb;
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        $this->prefix     = $mdb->get_prefix();
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        $this->temptables = array();
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    }
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    /**
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     * Add one temptable to the store
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     *
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     * Given one moodle temptable name (without prefix), add it to the store, with the
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     * key being the original moodle name and the value being the real db temptable name
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     * already prefixed
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     *
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     * Override and use this *only* if the database requires modification in the table name.
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     *
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     * @param string $tablename name without prefix of the table created as temptable
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     */
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    public function add_temptable($tablename) {
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        // TODO: throw exception if exists: if ($this->is_temptable...
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        $this->temptables[$tablename] = $tablename;
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    }
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    /**
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     * Delete one temptable from the store
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     *
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     * @param string $tablename name without prefix of the dropped temptable
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     */
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    public function delete_temptable($tablename) {
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        // TODO: throw exception if not exists: if (!$this->is_temptable....
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        unset($this->temptables[$tablename]);
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    }
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    /**
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     * Returns all the tablenames (without prefix) existing in the store
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     *
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     * @return array containing all the tablenames in the store (tablename both key and value)
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     */
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    public function get_temptables() {
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        return $this->temptables;
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    }
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    /**
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     * Returns if one table, based in the information present in the store, is a temp table
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     *
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     * @param string $tablename name without prefix of the table we are asking about
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     * @return bool true if the table is a temp table (based in the store info), false if not
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     */
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    public function is_temptable($tablename) {
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        return !empty($this->temptables[$tablename]);
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    }
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    /**
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     * Given one tablename (no prefix), return the name of the corresponding temporary table,
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     * If the table isn't a "registered" temp table, returns null
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     *
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     * @param string $tablename name without prefix which corresponding temp tablename needs to know
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     * @return mixed DB name of the temp table or null if it isn't a temp table
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     */
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    public function get_correct_name($tablename) {
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        if ($this->is_temptable($tablename)) {
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            return $this->temptables[$tablename];
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        }
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        return null;
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    }
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    /**
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     * Analyze the data in temporary tables to force statistics collection after bulk data loads.
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     * The database class detects all temporary tables and will automatically analyze all created tables
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     *
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     * @return void
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     */
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    public function update_stats() {
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        // By default most databases do automatic on temporary tables, PgSQL does not.
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        // As a result, update_stats call immediately return for non-interesting database types.
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    }
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    /**
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     * Dispose the temptables stuff, checking for wrong situations, informing and recovering from them
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     */
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    public function dispose() {
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        // We shouldn't have any temp table registered at the end of the script.
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        // So we error_log that and, at the same time, drop all the pending temptables
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        if ($temptables = $this->get_temptables()) {
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            error_log('Potential coding error - existing temptables found when disposing database. Must be dropped!');
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            foreach ($temptables as $temptable) {
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                 $this->mdb->get_manager()->drop_table(new xmldb_table($temptable));
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            }
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        }
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        $this->mdb = null;
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    }
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}