在Prestashop 1.6.1.6中通过“作者”进行自定义搜索

I'm building an online bookstore with Prestashop 1.6.1.6. Since the field "author" is not on the database, I've created this custom product field, but I am unable to perform searches by author's name.

Following this blog I have written this piece of code in "Search.php" but blog directions are for an older version and I have the least clue to re-write the class.

public static function getAuthors ($db, $id_product)
     {
     $authors ='';
     $authorsArray = $db->executeS('
        SELECT a.name FROM '._DB_PREFIX_. 'author sp
        LEFT JOIN '._DB_PREFIX_. 'author a ON (a.id_product = sp.id_product)
        WHERE sp.id_product = '. (int)$id_product. '
        GROUP BY a.id_product'
        ); 
        foreach ($authorsArray as $author){
            $authors. = $authors['name'] .'';
        }
        return $authors;
     }

/ Every fields are weighted according to the configuration in the backend
        $weight_array = array(
            'pname' => Configuration::get('PS_SEARCH_WEIGHT_PNAME'),
            //Add author to index search
            'author' => Configuration::get('PS_SEARCH_WEIGHT_PNAME'),
            'reference' => Configuration::get('PS_SEARCH_WEIGHT_REF'),
            'pa_reference' => Configuration::get('PS_SEARCH_WEIGHT_REF'),
            'supplier_reference' => Configuration::get('PS_SEARCH_WEIGHT_REF'),
            'pa_supplier_reference' => Configuration::get('PS_SEARCH_WEIGHT_REF'),
            'ean13' => Configuration::get('PS_SEARCH_WEIGHT_REF'),
            'pa_ean13' => Configuration::get('PS_SEARCH_WEIGHT_REF'),
            'upc' => Configuration::get('PS_SEARCH_WEIGHT_REF'),
            'pa_upc' => Configuration::get('PS_SEARCH_WEIGHT_REF'),
            'description_short' => Configuration::get('PS_SEARCH_WEIGHT_SHORTDESC'),
            'description' => Configuration::get('PS_SEARCH_WEIGHT_DESC'),
            'cname' => Configuration::get('PS_SEARCH_WEIGHT_CNAME'),
            'mname' => Configuration::get('PS_SEARCH_WEIGHT_MNAME'),
            'tags' => Configuration::get('PS_SEARCH_WEIGHT_TAG'),
            'attributes' => Configuration::get('PS_SEARCH_WEIGHT_ATTRIBUTE'),
            'features' => Configuration::get('PS_SEARCH_WEIGHT_FEATURE') 

);

Thanks for reading.