MDL-15181 cross-db temporary tables support. First-cut.

lib/dml/moodle_temptables.php

@@ -0,0 +1,111 @@
+<?php
+
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+/**
+ * Generic temptables object store
+ *
+ * Provides support to databases lacking some "expeted behaviour" related
+ * with some operations with temporary tables like:
+ *
+ *   - databases not retrieving temp tables from information schema tables (mysql)
+ *   - databases using a different name schema for temp tables (like mssql).
+ *
+ * Basically it works as a simple store of created temporary tables, providing
+ * some simple getters/setters methods. Each database can extend it for its own
+ * purposes (for example, return correct name, see the mssql implementation)
+ *
+ * The unique instance of the object by database connection is shared by the database
+ * and the sql_generator, so both are able to use its facilities, with the final goal
+ * of doing temporary tables support 100% cross-db and transparent within the DB API.
+ *
+ * Only drivers needing it will use this store. Neither moodle_database (abstract) or
+ * databses like postgres need this, because they don't lack any temp functionality.º:w
+
+ *
+ * @package    moodlecore
+ * @subpackage DML
+ * @copyright  2009 onwards Eloy Lafuente (stronk7) {@link http://stronk7.com}
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+class moodle_temptables {
+
+    protected $mdb;        // circular reference, to be able to use DB facilities here if needed
+    protected $prefix;     // prefix to be used for all the DB objects
+    protected $temptables; // simple array of 'tablename' => 'tablename'
+
+    /**
+     * Creates new moodle_temptables instance
+     * @param object moodle_database instance
+     */
+    public function __construct($mdb) {
+        $this->mdb        = $mdb;
+        $this->prefix     = $mdb->get_prefix();
+        $this->temptables = array();
+    }
+
+    /**
+     * Add one temptable to the store
+     *
+     * @param string $tablename name without prefix of the table created as temptable
+     */
+    public function add_temptable($tablename) {
+        // TODO: throw exception if exists: if ($this->is_temptable...
+        $this->temptables[$tablename] = $tablename;
+    }
+
+    /**
+     * Delete one temptable from the store
+     *
+     * @param string $tablename name without prefix of the dropped temptable
+     */
+    public function delete_temptable($tablename) {
+        // TODO: throw exception if not exists: if (!$this->is_temptable....
+        unset($this->temptables[$tablename]);
+    }
+
+    /**
+     * Returns all the tablenames (without prefix) existing in the store
+     *
+     * @return array containing all the tablenames in the store (tablename both key and value)
+     */
+    public function get_temptables() {
+        return $this->temptables;
+    }
+
+    /**
+     * Returns if one table, based in the information present in the store, is a temp table
+     *
+     * @param string $tablename name without prefix of the table we are asking about
+     * @return bool true if the table is a temp table (based in the store info), false if not
+     */
+    function is_temptable ($tablename) {
+        return !empty($this->temptables[$tablename]);
+    }
+
+    /**
+     * Given one tablename (no prefix), return the name of the corresponding temporary table,
+     * usually the same name but some databases could require changes (like '#' prefix in mssql)
+     *
+     * Override and use this *only* if the database requires modification in the table name.
+     *
+     * @param string $tablename name without prefix which corresponding temp tablename nees to calculate
+     */
+    public function get_correct_name($tablename) {
+        return $this->prefix . $tablename; // No change in name is the usual behaviour
+    }
+}

lib/dml/mssql_native_moodle_temptables.php

@@ -0,0 +1,48 @@
+<?php
+
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+/**
+ * MSSQL specific temptables store. Needed because temporary tables
+ * are named diferently than normal tables. Also used to be able to retrieve
+ * temp table names included in the get_tables() method od the DB.
+ *
+ * @package    moodlecore
+ * @subpackage DML
+ * @copyright  2009 onwards Eloy Lafuente (stronk7) {@link http://stronk7.com}
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+require_once($CFG->libdir.'/dml/moodle_temptables.php');
+
+class mssql_native_moodle_temptables extends moodle_temptables {
+
+    /**
+     * Override the method to return the correct real name (prefix = '#') of
+     * temporary mssql databases. Widely used in the corresponding mssql sql
+     * generator and database driver
+     *
+     * @param string $tablename name without prefix which corresponding temp tablename nees to calculate
+     */
+    public function get_correct_name($tablename) {
+        // TODO: throw exception if not exists
+        if (!empty($this->temptables[$tablename])) {
+            return '#' . $this->prefix . $tablename;
+        } else {
+            return $this->prefix . $tablename;
+        }
+    }
+}