data_object.php

<?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/>.

/**
 * Course completion critieria aggregation
 *
 * @package core_completion
 * @category completion
 * @copyright 2009 Catalyst IT Ltd
 * @author Aaron Barnes <aaronb@catalyst.net.nz>
 * @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */

defined('MOODLE_INTERNAL') || die();


/**
 * Trigger for the new data_object api.
 *
 * See data_object::__constructor
 */
define('DATA_OBJECT_FETCH_BY_KEY',  2);

/**
 * A data abstraction object that holds methods and attributes
 *
 * @package core_completion
 * @category completion
 * @copyright 2009 Catalyst IT Ltd
 * @author Aaron Barnes <aaronb@catalyst.net.nz>
 * @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */
abstract class data_object {

    /* @var string Table that the class maps to in the database */
    public $table;

    /* @var array Array of required table fields, must start with 'id'. */
    public $required_fields = array('id');

    /**
     * Array of optional fields with default values - usually long text information that is not always needed.
     * If you want to create an instance without optional fields use: new data_object($only_required_fields, false);
     * @var array
     */
    public $optional_fields = array();

    /* @var Array of unique fields, used in where clauses and constructor */
    public $unique_fields = array();

    /* @var int The primary key */
    public $id;


    /**
     * Constructor. Optionally (and by default) attempts to fetch corresponding row from DB.
     *
     * If $fetch is not false, there are a few different things that can happen:
     * - true:
     *   load corresponding row from the database, using $params as the WHERE clause
     *
     * - DATA_OBJECT_FETCH_BY_KEY:
     *  load corresponding row from the database, using only the $id in the WHERE clause (if set),
     *  otherwise using the columns listed in $this->unique_fields.
     *
     * - array():
     *   load corresponding row from the database, using the columns listed in this array
     *   in the WHERE clause
     *
     * @param   array   $params     required parameters and their values for this data object
     * @param   mixed   $fetch      if false, do not attempt to fetch from the database, otherwise see notes
     */
    public function __construct($params = null, $fetch = true) {

        if (is_object($params)) {
            throw new coding_exception('data_object params should be in the form of an array, not an object');
        }

        // If no params given, apply defaults for optional fields
        if (empty($params) || !is_array($params)) {
            self::set_properties($this, $this->optional_fields);
            return;
        }

        // If fetch is false, do not load from database
        if ($fetch === false) {
            self::set_properties($this, $params);
            return;
        }

        // Compose where clause only from fields in unique_fields
        if ($fetch === DATA_OBJECT_FETCH_BY_KEY && !empty($this->unique_fields)) {
            if (empty($params['id'])) {
                $where = array_intersect_key($params, array_flip($this->unique_fields));
            }
            else {
                $where = array('id' => $params['id']);
            }
        // Compose where clause from given field names
        } else if (is_array($fetch) && !empty($fetch)) {
            $where = array_intersect_key($params, array_flip($fetch));
        // Use entire params array for where clause
        } else {
            $where = $params;
        }

        // Attempt to load from database
        if ($data = $this->fetch($where)) {
            // Apply data from database, then data sent to constructor
            self::set_properties($this, $data);
            self::set_properties($this, $params);
        } else {
            // Apply defaults for optional fields, then data from constructor
            self::set_properties($this, $this->optional_fields);
            self::set_properties($this, $params);
        }
    }

    /**
     * Makes sure all the optional fields are loaded.
     *
     * If id present (==instance exists in db) fetches data from db.
     * Defaults are used for new instances.
     */
    public function load_optional_fields() {
        global $DB;
        foreach ($this->optional_fields as $field=>$default) {
            if (property_exists($this, $field)) {
                continue;
            }
            if (empty($this->id)) {
                $this->$field = $default;
            } else {
                $this->$field = $DB->get_field($this->table, $field, array('id', $this->id));
            }
        }
    }

    /**
     * Finds and returns a data_object instance based on params.
     *
     * This function MUST be overridden by all deriving classes.
     *
     * @param array $params associative arrays varname => value
     * @throws coding_exception This function MUST be overridden
     * @return data_object instance  of data_object or false if none found.
     */
    public static function fetch($params) {
        throw new coding_exception('fetch() method needs to be overridden in each subclass of data_object');
    }

    /**
     * Finds and returns all data_object instances based on params.
     *
     * This function MUST be overridden by all deriving classes.
     *
     * @param array $params associative arrays varname => value
     * @throws coding_exception This function MUST be overridden
     * @return array array of data_object instances or false if none found.
     */
    public static function fetch_all($params) {
        throw new coding_exception('fetch_all() method needs to be overridden in each subclass of data_object');
    }

    /**
     * Factory method - uses the parameters to retrieve matching instance from the DB.
     *
     * @final
     * @param string $table The table name to fetch from
     * @param string $classname The class that you want the result instantiated as
     * @param array $params Any params required to select the desired row
     * @return object Instance of $classname or false.
     */
    protected static function fetch_helper($table, $classname, $params) {
        if ($instances = self::fetch_all_helper($table, $classname, $params)) {
            if (count($instances) > 1) {
                // we should not tolerate any errors here - problems might appear later
                print_error('morethanonerecordinfetch','debug');
            }
            return reset($instances);
        } else {
            return false;
        }
    }

    /**
     * Factory method - uses the parameters to retrieve all matching instances from the DB.
     *
     * @final
     * @param string $table The table name to fetch from
     * @param string $classname The class that you want the result instantiated as
     * @param array $params Any params required to select the desired row
     * @return mixed array of object instances or false if not found
     */
    public static function fetch_all_helper($table, $classname, $params) {
        $instance = new $classname();

        $classvars = (array)$instance;
        $params    = (array)$params;

        $wheresql = array();

        foreach ($params as $var=>$value) {
            if (!in_array($var, $instance->required_fields) and !array_key_exists($var, $instance->optional_fields)) {
                continue;
            }
            if (is_null($value)) {
                $wheresql[] = " $var IS NULL ";
            } else {
                $wheresql[] = " $var = ? ";
                $params[] = $value;
            }
        }

        if (empty($wheresql)) {
            $wheresql = '';
        } else {
            $wheresql = implode("AND", $wheresql);
        }

        global $DB;
        if ($datas = $DB->get_records_select($table, $wheresql, $params)) {

            $result = array();
            foreach($datas as $data) {
                $instance = new $classname();
                self::set_properties($instance, $data);
                $result[$instance->id] = $instance;
            }
            return $result;

        } else {

            return false;
        }
    }

    /**
     * Updates this object in the Database, based on its object variables. ID must be set.
     *
     * @return bool success
     */
    public function update() {
        global $DB;

        if (empty($this->id)) {
            debugging('Can not update data object, no id!');
            return false;
        }

        $data = $this->get_record_data();

        $DB->update_record($this->table, $data);

        $this->notify_changed(false);
        return true;
    }

    /**
     * Deletes this object from the database.
     *
     * @return bool success
     */
    public function delete() {
        global $DB;

        if (empty($this->id)) {
            debugging('Can not delete data object, no id!');
            return false;
        }

        $data = $this->get_record_data();

        if ($DB->delete_records($this->table, array('id'=>$this->id))) {
            $this->notify_changed(true);
            return true;

        } else {
            return false;
        }
    }

    /**
     * Returns object with fields and values that are defined in database
     *
     * @return stdClass
     */
    public function get_record_data() {
        $data = new stdClass();

        foreach ($this as $var=>$value) {
            if (in_array($var, $this->required_fields) or array_key_exists($var, $this->optional_fields)) {
                if (is_object($value) or is_array($value)) {
                    debugging("Incorrect property '$var' found when inserting data object");
                } else {
                    $data->$var = $value;
                }
            }
        }
        return $data;
    }

    /**
     * Records this object in the Database, sets its id to the returned value, and returns that value.
     * If successful this function also fetches the new object data from database and stores it
     * in object properties.
     *
     * @return int PK ID if successful, false otherwise
     */
    public function insert() {
        global $DB;

        if (!empty($this->id)) {
            debugging("Data object already exists!");
            return false;
        }

        $data = $this->get_record_data();

        $this->id = $DB->insert_record($this->table, $data);

        // set all object properties from real db data
        $this->update_from_db();

        $this->notify_changed(false);
        return $this->id;
    }

    /**
     * Using this object's id field, fetches the matching record in the DB, and looks at
     * each variable in turn. If the DB has different data, the db's data is used to update
     * the object. This is different from the update() function, which acts on the DB record
     * based on the object.
     *
     * @return bool True for success, false otherwise.
     */
    public function update_from_db() {
        if (empty($this->id)) {
            debugging("The object could not be used in its state to retrieve a matching record from the DB, because its id field is not set.");
            return false;
        }
        global $DB;
        if (!$params = $DB->get_record($this->table, array('id' => $this->id))) {
            debugging("Object with this id:{$this->id} does not exist in table:{$this->table}, can not update from db!");
            return false;
        }

        self::set_properties($this, $params);

        return true;
    }

    /**
     * Given an associated array or object, cycles through each key/variable
     * and assigns the value to the corresponding variable in this object.
     *
     * @final
     * @param data_object $instance
     * @param array $params
     */
    public static function set_properties(&$instance, $params) {
        $params = (array) $params;
        foreach ($params as $var => $value) {
            if (in_array($var, $instance->required_fields) or array_key_exists($var, $instance->optional_fields)) {
                $instance->$var = $value;
            }
        }
    }

    /**
     * Called immediately after the object data has been inserted, updated, or
     * deleted in the database. Default does nothing, can be overridden to
     * hook in special behaviour.
     *
     * @param bool $deleted Set this to true if it has been deleted.
     */
    public function notify_changed($deleted) {
    }
}