Codeigniter ผมไม่สามารถ Update ข้อมูลได้อะครับช่วยดูให้หน่อยครับ

public function ajax_update()
    {
         $data = array(
                'placename' => $this->input->post('placename'),
                'description' => $this->input->post('description'),
                'tel' => $this->input->post('tel'),
                'latitude' => $this->input->post('latitude'),
                'longtitude' => $this->input->post('longtitude'),
                'placetype_id' => $this->input->post('placetype_id'),
                'province_id' => $this->input->post('province_id'),
                
            );
        $this->tblplace->update(array('placeid' => $this->input->post('placeid')), $data);
        echo json_encode(array("status" => TRUE));
    }

 public function update($where, $data)
    {
        $this->db->update('tblplace', $data, $where);
        return $this->db->affected_rows();
    }

function save()
{
    $('#btnSave').text('saving...'); //change button text
    $('#btnSave').attr('disabled',true); //set button disable 
    var url;

    if(save_method == 'add') {
        url = "<?php echo site_url('index.php/places/ajax_add')?>";
    } else {
        url = "<?php echo site_url('index.php/places/ajax_update')?>";
    }

    // ajax adding data to database
    $.ajax({
        url : url,
        type: "POST",
        data: $('#form').serialize(),
        dataType: "JSON",
        success: function(data)
        {

            if(data.status) //if success close modal and reload ajax table
            {
                $('#modal_form').modal('hide');
                reload_table();
            }

            $('#btnSave').text('save'); //change button text
            $('#btnSave').attr('disabled',false); //set button enable 


        },
        error: function (jqXHR, textStatus, errorThrown)
        {
            alert('Error adding / update data');
            $('#btnSave').text('save'); //change button text
            $('#btnSave').attr('disabled',false); //set button enable 

        }
    });
}