Method __construct

/**
 * Constructor: builds array of $changeItems by processing the .sql files in a folder.
 * The folder for the Joomla core updates is `administrator/components/com_admin/sql/updates/<database>`.
 *
 * @param   DatabaseDriver  $db      The current database object
 * @param   string          $folder  The full path to the folder containing the update queries
 *
 * @since   2.5
 */
public function __construct($db, $folder = null)
{
    $this->db = $db;
    $this->folder = $folder;
    $updateFiles = $this->getUpdateFiles();
    // If no files were found nothing more we can do - continue
    if ($updateFiles === false) {
        return;
    }
    $updateQueries = $this->getUpdateQueries($updateFiles);
    foreach ($updateQueries as $obj) {
        $this->changeItems[] = ChangeItem::getInstance($db, $obj->file, $obj->updateQuery);
    }
    // If on mysql, add a query at the end to check for utf8mb4 conversion status
    if ($this->db->getServerType() === 'mysql') {
        // Check if the #__utf8_conversion table exists
        $this->db->setQuery('SHOW TABLES LIKE ' . $this->db->quote($this->db->getPrefix() . 'utf8_conversion'));
        try {
            $rows = $this->db->loadRowList(0);
            $tableExists = \count($rows);
        } catch (\RuntimeException $e) {
            $tableExists = 0;
        }
        // If the table exists add a change item for utf8mb4 conversion to the end
        if ($tableExists > 0) {
            // Let the update query do nothing
            $tmpSchemaChangeItem = ChangeItem::getInstance($db, 'database.php', 'UPDATE ' . $this->db->quoteName('#__utf8_conversion') . ' SET ' . $this->db->quoteName('converted') . ' = ' . $this->db->quoteName('converted') . ';');
            // Set to not skipped
            $tmpSchemaChangeItem->checkStatus = 0;
            // Set the check query
            $tmpSchemaChangeItem->queryType = 'UTF8_CONVERSION_UTF8MB4';
            $tmpSchemaChangeItem->checkQuery = 'SELECT ' . $this->db->quoteName('converted') . ' FROM ' . $this->db->quoteName('#__utf8_conversion') . ' WHERE ' . $this->db->quoteName('converted') . ' = 5';
            // Set expected records from check query
            $tmpSchemaChangeItem->checkQueryExpected = 1;
            $tmpSchemaChangeItem->msgElements = array();
            $this->changeItems[] = $tmpSchemaChangeItem;
        }
    }
}