Wywołać metodę niezdefiniowaną ci_db_mysqli_result :: Order_By ()
In CodeIgniter's Active Record, every method returns the object itself (which allows method chaining) except for get and get_where which return the result set.
Thus, what you need to do is:
$query = $this->db->order_by('birth_date', 'ASC')->get_where($this->tbl_name, $where);
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