codeigniter dependent dropdown error

This is my code. It does not work with codeigniter 3.0 and jquery. I need to use dropdown dependent so I made that but it will be display "Error occur..." by alert() after choosing any item in first dropdown.

Please have a look to my source code. I don't know what is wrong. Thanks everyone

VIEW:

    <script type="text/javascript">
    $(document).ready(function(){
        $('#senf').on('change', function(){
            var senf_id = $(this).val();
            if(senf_id == '')
            {
                $('#raste').prop('disabled', true);
            }
            else
            {
                $('#raste').prop('disabled', false);
                $.ajax({
                    url:"<?php echo base_url() ?>index.php/shoppings/get_subgroup/",
                    type: "POST",
                    data: {'senf_id' : senf_id},
                    dataType: 'json',
                    success: function(data){
                        alert('okkk');
                    },
                    error: function(){
                        alert('Error occur...!!');
                    }
                });
            }
        });
    });
</script>
<div class="form-group ">
<label for="group_name" class="control-label col-lg-2">group 1</label>
<select id="senf" name="group">
    <option value="" selected="selected">select</option>
    <?php
    foreach ($get_groups as $value) {
        $group_id = $value['group_shop_id'];
        $group_name = $value['group_shop_name'];
    ?>
    <option value="<?php echo $group_id; ?>"> <?php echo $group_name; ?> </option>
    <?php } ?>
</select>

<label for="raste" >group 2</label>
<select id="raste" name="raste">
    <option value="">select</option>
</select>
</div>
CONTROLLER:

    public function get_subgroup(){
    $id = $this->input->post('senf_id');
    $ajax_get_subgroup = $this->shopping_model->ajax_get_subgroup($id);
        $pro_select_box = '';
        $pro_select_box .= '<option value="">Select Province</option>';
        foreach($ajax_get_subgroup as $ajax_get_subgroup_value){
            $pro_select_box .= '<option>'. $ajax_get_subgroup_value->cat_shop_name .'</option>';
        }
        echo json_encode($pro_select_box);
}
MODEL:

    public function ajax_get_subgroup($id){
    $query = $this->db->get_where('cat_shopping_group omegle shagle voojio ', array('group_shop_id' => $id));
    return $query->result();
}

Controller

public function ajax_get_subgroup()
{
extract($_POST);
$tmp='';
$sql = "SELECT * FROM cat_shopping_group where group_shop_id=$id";
$data = $this->db->query($sql)->result_array();
$tmp .="<option value=''>-- Select --</option>";
foreach($data as $row)
{
$tmp .="<option value='".$row['your_id']."'>".$row['cat_shop_name ']."</option>";
}
die($tmp);
}`
AJAX

function get_data()
{
var id = $('#senf').val()

datana= 'id='+id
$.ajax({
type: 'POST',
url: '<?=base_url()?>your_controller/ajax_get_subgroup',
data: datana,
error: function(data) {
alert('Failed');
},
success: function(data)
{
$('#raste').html(data)
}
})
}
Views

<select id="senf" name="group" onchange='ajax_get_subgroup();'>
<option value="" selected="selected">select</option>
<?php
your code
?>
</select>
<select id="raste">
</select>
Hope this help.