使用ajax select选项更新数据

when I select the data that I want to update, it turns out the data displayed in the last data is in the database, but when it is filled in the data changes according to the data selected by the data, is there anything in the file controler and the ajax form view

this file contrroler

function get_edit(){
        $id_item2 = $this->uri->segment(3);
        $data['id_item2'] = $id_item2;
        $data['Bobot'] = $this->Item2_model->get_category()->result();
        $get_data = $this->Item2_model->get_item_by_id($id_item2);
        if($get_data->num_rows() > 0){
            $row = $get_data->row_array();
            $data['id_item'] = $row['id_bobot']; 
        }
        $this->load->view('Admin/kpi_item2-formupdate',$data);
    }

     function get_data_edit(){
        $id_item2 = $this->input->post('id_item2',TRUE);
        $data = $this->Item2_model->tampil_data_item2($id_item2)->result();
        echo json_encode($data);
    }

this the view form after klik edit

<div class="col-md-13 col-sm-12"><label>KPI Group Name</label><select class="form-control" id="id_bobot" name="id_bobot"  style="width: 100%;">  <option value="">No Selected</option>
                        <?php foreach($Bobot as $row):?>   <option value="<?php echo $row->id_bobot;?>"><?php echo $row->KPI_group;?></option>
                        <?php endforeach;?>  </select>   </div><br><div class="col-md-13 col-sm-12">
<label >Parameter KPI</label><select class="form-control " name="id_item"  id="id_item" style="width: 100%;">

                          <option value="">No Selected</option> 

        </select></div><div class="col-md-13 col-sm-12">
<label >Item Parameter KPI</label><input type="text" name="parameter2" class="form-control"  required   ></div><div class="col-md-2 col-sm-12"> <div class="form-group"> <label for="input-id_jabatan-en">Bobot (Bulan)</label> <input type="text" name="bobot_bulan2" class="form-control"   required  ></div></div></pre>
          </div></pre>    <input type="text" name="id_item2" value="<?php echo $id_item2?>" required>

                          <button class="btn btn-success" type="submit">Save</button>

                        </form>
                </div>
            </div>

<script type="text/javascript">
        $(document).ready(function(){
            //call function get data edit
            get_data_edit();

            $('#id_bobot').change(function(){ 
                var id=$(this).val();
                var subcategory_id = "<?php echo $id_item;?>";
                $.ajax({
                    url : "<?php echo site_url('HomeAdmin/get_sub_category');?>",
                    method : "POST",
                    data :{ id: id},
                    async : true,
                    dataType : 'json',
                    success: function(data){

                        $('select[name="id_item"]').empty();

                        $.each(data, function(key, value) {
                            if(subcategory_id==value.subcategory_id){
                                $('select[name="id_item"]').append('<option value="'+ value.
                                  subcategory_id +'" selected>'+ value.parameter+'</option>').
                                  trigger('change');
                            }else{
                                $('select[name="id_item"]').append('<option value="'+ value.
                                  subcategory_id +'">'+ value.parameter +'</option>');
                            }
                        });

                    }
                });
                return false;
            }); 

            //load data for edit
            function get_data_edit(){

                var  id2 = $('[name="id_item2"]').val();
                $.ajax({
                    url : "<?php echo site_url('HomeAdmin/get_data_edit');?>",
                    method : "POST",
                    data :{ id2 : id2},
                    async : true,
                    dataType : 'json',
                    success : function(data){
                        $.each(data, function(i, item){
                              $('[name="parameter2"]').val(data[i].parameter2);
                            $('[name="bobot_bulan2"]').val(data[i].bobot_bulan2);
                            $('[name="id_bobot"]').val(data[i].id_bobot).trigger('change');
                            $('[name="id_item"]').val(data[i].parameter).trigger('change');

                        });
                    }

                });
            }

        });
    </script>

and this file model

function get_sub_category($id_item){
        $query = $this->db->get_where('kpi_item', array('id_bobot' => $id_item));
        return $query;
    }

    function get_category(){
        $query = $this->db->get('bobot_db');
        return $query;  
    }

    function get_item_by_id($id_item2){
        $query = $this->db->get_where('kpi_item2', array('id_item2' =>  $id_item2));
        return $query;
    }


    function tampil_data_item2(){
        $this->db->select('p.*, k.KPI_group,s.parameter');
        $this->db->from('kpi_item2 p');
        $this->db->join('bobot_db k','p.id_bobot = k.id_bobot');
        $this->db->join('kpi_item s','s.id_item  = p.id_item');
        $hasil=$this->db->get();
        return $hasil;
    }