Recommendation

[crazedVic]

I would recommend adding self::_getPDO()->quote($where) to the following function. This will prevent characters like ' from making the query invalid.

public static function where($where, $params = [], $order = null, $limit = null, $index = 0)
    {
        if ($where === '') {
            $query = 'SELECT * FROM `' . self::getTable() . '` ' . self::order($order) . self::limit($limit, $index);
        } else {
            $query = 'SELECT * FROM `' . self::getTable() . '` WHERE ' . self::_getPDO()->quote($where) . self::order($order) . self::limit($limit, $index);
        }
        return self::query($query, $params);
    }

[erwang]

You don't need this, you must use params request :
Object::where('birthDate between :date1 and :date2',['date1'=>'2000-01-01','date2'=>'2000-12-31']);