下拉依赖于codeigniter活动记录

Question

当您在类表中选择名称时，付款条件将基于sql表（请参见sql表），这使我很难确定如何建立下拉依赖关系（付款条件基于选定的类名）。最后一张表）基于类级别的选择。我认为我的JavaScript和CI模型有问题。我在这个codeigniter活动记录中非常陌生，请帮助我解决我的问题，并非常感谢您

CLASS TABLE

  classes
  |-------|------------------|
  |  id   |       Name       |
  |-------|------------------|
  |   1   |   Grade 1        |
  |-------|------------------|
  |   2   |   Grade 2        |
  |-------|------------------|

付款条款表

  payment_terms
  |--------|------------------------------------|
  |   id   |       payment_terms                |
  |--------|------------------------------------|
  |   1    |   Grade 1    Full Payment          |
  |--------|------------------------------------|
  |   2    |   Grade 1    Quarterly Payment     |
  |--------|------------------------------------|
  |   3    |   Grade 2    Full Payment          |
  |--------|------------------------------------|
  |   4    |   Grade 2    Quarterly Payment     |
  |--------|------------------------------------|

学术年表

  academic_year 
  |--------|------------------------------------|
  |   id   |       academic_year                |
  |--------|------------------------------------|
  |   1    |         2018-2019                  |
  |--------|------------------------------------|

学术年度和付款条款表

  academic_year_payment_terms
  |--------|------------------|------------------|
  |   id   | academic_year_id | Payment_term_id  |
  |--------|------------------|------------------|
  |   1    | 1                | 1                |
  |--------|------------------|------------------|
  |   2    | 1                | 2                |
  |--------|------------------|------------------|
  |   3    | 1                | 3                |
  |--------|------------------|------------------|
  |   4    | 1                | 4                |
  |--------|------------------|------------------|

学术年度付款条款和分类表

  academic_year_payment_terms_class
  |--------|-----------------------------|------------------|
  |   id   | academic_year_payment_terms | class_id         |
  |--------|-----------------------------|------------------|
  |   1    | 1                           | 1                |
  |--------|-----------------------------|------------------|
  |   2    | 2                           | 1                |
  |--------|-----------------------------|------------------|
  |   3    | 3                           | 2                |
  |--------|-----------------------------|------------------|
  |   4    | 4                           | 2                |
  |--------|-----------------------------|------------------|

我的Codeigniter视图

<div class="form-group">
  <select  id="class_id" name="class_id" class="form-control" >
     <option value=""><?php echo $this->lang->line('select'); ?></option>
         <?php
            foreach ($classlist as $class) { ?>
           <option value="<?php echo $class['id'] ?>"<?php
               if (set_value('class_id') == $class['id']){
                    echo "selected =selected";
               }
               ?>><?php echo $class['class'] ?></option>
            <?php
               $count++;
            }
            ?>
  </select>
</div>
<div class="form-group">
  <select class="form-control" id="academic_year_payment_terms_id" name="academic_year_payment_terms_id">
  </select>
</div>

我的JavaScript

<script type="text/javascript">
function getAcademicPaymentTermsByClass(class_id, academic_year_payment_terms_id {
    if (class_id != "" && academic_year_payment_terms_id != "") {
        $('#academic_year_payment_terms_id').html("");
        var base_url = '<?php echo base_url() ?>';
        var div_data = '<option value=""><?php echo $this->lang->line('select'); ?></option>';
        $.ajax({
            type: "GET",
            url: base_url + "enrollment/fetchPaymentTermsByClass",
            data: {'class_id': class_id},
            dataType: "json",
            success: function (data) {
                $.each(data, function (i, obj)
                {
                    var sel = "";
                    if (academic_year_payment_terms_id == obj.academic_year_payment_terms_id) {
                        sel = "selected";
                    }

                    div_data += "<option value=" + obj.academic_year_payment_terms_id+ " " + sel + ">" + obj.payment_terms + "</option>";
                });
                $('#academic_year_payment_terms_id').append(div_data);
            }
        });
    }
}

$(document).ready(function () {
    var class_id = $('#class_id').val();
    var academic_year_payment_terms_id = '<?php echo set_value('academic_year_payment_terms_id') ?>';
    getAcademicPaymentTermsByClass(class_id, academic_year_payment_terms_id);

    $(document).on('change', '#class_id', function (e) {
        $('#academic_year_payment_terms_id').html("");
        var class_id = $(this).val();
        var base_url = '<?php echo base_url() ?>';
        var div_data = '<option value=""><?php echo $this->lang->line('select'); ?></option>';
        $.ajax({
            type: "GET",
            url: base_url + "enrollment/fetchPaymentTermsByClass",
            data: {'class_id': class_id},
            dataType: "json",
            success: function (data) {
                $.each(data, function (i, obj)
                {

                    div_data += "<option value=" + obj.academic_year_payment_terms_id' + ">" + obj.payment_terms' + "</option>";
                });
                $('#academic_year_payment_terms_id').append(div_data);
            }
        });
    });
});

我的注册负责人

   function fetchPaymentTermsByClass() {
    $class_id = $this->input->get('class_id');
    $data = $this->Enrollment_model->getPaymentTermsByClass($class_id);
    echo json_encode($data);
   }

我的注册模型

   public function getPaymentTermsByClass($classid){
    $this->db->select('academic_year_payment_terms_class.id, academic_year_payment_terms_class.academic_year_payment_terms_id, academic_year_payment_terms.payment_terms');
    $this->db->from('academic_year_payment_terms_class');
    $this->db->join('academic_year_payment_terms', 'academic_year_payment_terms.id = academic_year_payment_terms_class.academic_year_payment_terms_id');
    $this->db->where('academic_year_payment_terms_class.class_id', $classid);
    $this->db->order_by('academic_year_payment_terms_class.id');
    $query = $this->db->get();
    return $query->result_array();
    }