Adding an attribute by plugins (Solution 2)

addAnAttribute.php

<?php
/**
 * extend admin statitics with own controller extending the LS core controller
 *
 * @author Denis Chenu <denis@sondages.pro>
 * @copyright 2016 Denis Chenu <http://www.sondages.pro>
 * @license WTFPL
 * @version 0.0.0
 *
 * This program 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.
 *
 * This program 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.
 */
class addAnAttribute extends PluginBase
{

    protected $storage = 'DbStorage';

    static protected $name = 'addAnAttribute';
    static protected $description = 'Add an attribute for any question';
    public function init()
    {
        $this->subscribe('newQuestionAttributes');
        $this->subscribe('beforeQuestionRender');
    }
    public function newQuestionAttributes()
    {
        $event = $this->getEvent();
        $questionAttributes = array(
            'exampleOne'=>array(
                "types"=>"L",
                'category'=>gT('Other'),
                'sortorder'=>1,
                'inputtype'=>'text',
                'default'=>'',
                "help"=>'An example for text.',
                "caption"=>'A text attribute'
            ),
            'exampleTwo'=>array(
                "types"=>"L",
                'category'=>gT('Other'),
                'sortorder'=>2,
                'inputtype'=>'singleselect',
                'options'=>array(
                    0=>gT('No'),
                    1=>gT('No'),
                ),
                'default'=>0,
                "help"=>'An example for singleselect.',
                "caption"=>'A text attribute'
            ),
        );
        $event->append('questionAttributes', $questionAttributes);
    }

    public function beforeQuestionRender()
    {
        $oAttributeOne=QuestionAttribute::model()->find("qid=:qid AND attribute=:attribute",array(":qid"=>$oEvent->get('qid'),":attribute"=>"exampleOne"));
        $oAttributeTwo=QuestionAttribute::model()->find("qid=:qid AND attribute=:attribute",array(":qid"=>$oEvent->get('qid'),":attribute"=>"exampleTwo"));
        /* OR */
        $aAttributes=QuestionAttribute::model()->getQuestionAttributes($oEvent->get('qid'));
        $soAttributeOne=$aAttributes["exampleOne"];
        $soAttributeTwo=$aAttributes["exampleTwo"];
        /**
         * Do something
         */

    }
}