jquery数据表搜索和排序不起作用

I use data tables library for CodeIgniter, but when I try to sort a column I get the same table, but the ajax request is working. Here is my model.

public function get_users()
{
    $this->load->library('datatables');
    $this->datatables->select('users.id, users.username, users.email, users.created_at, users.updated_at, users.status, users_roles.role',false);

    $this->datatables->where('users.role_id = users_roles.id');
    $this->datatables->from('users, users_roles');

    return $this->datatables->generate();
}

My controller :

public function get_users(){
    log_message('INFO',var_export($this->input->post(),true));
    $this->load->model('user_model');
    echo  $this->user_model->get_users();

}

And my view :

<script>
jQuery(document).ready(function() {

    jQuery('#users_table').DataTable({
        'iDisplayLength':10,
        'bLengthChange': true,
        'processing': true,
        'serverSide':true,
        'responsive': true,
        'bFilter': true,
        'bSort': true,
        'columns': [
            {
                'data': 'username',
                'bSortable': true,
                'defaultContent': 'N/A',
                'bSearchable' : true
            },
            {
                'data': 'email',
                'bSortable': true,
                'defaultContent': 'N/A',
                'bSearchable' : true
            },
            {
                'data': 'created_at',
                'bSortable': true,
                'defaultContent': 'N/A',
                'bSearchable' : true
            },
            {
                'data': 'updated_at',
                'bSortable': true,
                'defaultContent': 'N/A',
                'bSearchable' : true
            },
            {
                'data': 'role',
                'bSortable': true,
                'defaultContent': 'N/A',
                'bSearchable' : true
            },
            {
                'data': 'status',
                'bSortable': true,
                'defaultContent': 'N/A',
                'bSearchable' : true
            },
            {
                'data': '',
                'bSortable': false,
                'defaultContent': '<button type="button" class="btn btn-info edit_user" style="text-align: center">Edit</button><button type="button" class="btn btn-info delete_user" style="text-align: center">Delete</button>',
                'bSearchable' : false
            }],
        "order": [[ 3, "desc" ]],
        'sAjaxSource':'/admin/users/get_users/',
        'fnServerData': function (sSource, aoData, fnCallback) {
            jQuery.ajax({
                'dataType': 'json',
                'type':'POST',
                'url':sSource,
                'data':aoData,
                'success':fnCallback
            }).done(function(response){
                console.log("asdad");
            });
        },
        'rowCallback': function(nRow, aData){
            jQuery(nRow).attr('data-id', aData['id']);
        }
    });
});

When I try to make a search or order I get this in post : INFO - 2016-10-31

16:31:42 --> array ( 'sEcho' => '3', 'iColumns' => '7',
'sColumns' => ',,,,,,', 'iDisplayStart' => '0', 'iDisplayLength' => '10', 'mDataProp_0' => 'name', 'sSearch_0' => '', 'bRegex_0' => 'false', 'bSearchable_0' => 'true', 'bSortable_0' => 'true', 'mDataProp_1' => 'description', 'sSearch_1' => '', 'bRegex_1' => 'false', 'bSearchable_1' => 'true', 'bSortable_1' => 'true',
'mDataProp_2' => 'price', 'sSearch_2' => '', 'bRegex_2' => 'false', 'bSearchable_2' => 'true', 'bSortable_2' => 'true',
'mDataProp_3' => 'url', 'sSearch_3' => '', 'bRegex_3' => 'false', 'bSearchable_3' => 'true', 'bSortable_3' => 'true', 'mDataProp_4' => 'add_date', 'sSearch_4' => '', 'bRegex_4' => 'false', 'bSearchable_4' => 'true', 'bSortable_4' => 'true', 'mDataProp_5' => 'status', 'sSearch_5' => '', 'bRegex_5' => 'false', 'bSearchable_5' => 'true', 'bSortable_5' => 'true', 'mDataProp_6' => '', 'sSearch_6' => '', 'bRegex_6' => 'false', 'bSearchable_6' => 'true', 'bSortable_6' => 'false', 'sSearch' => '', 'bRegex' => 'false', 'iSortCol_0' => '0', 'sSortDir_0' => 'desc', 'iSortingCols' => '1', )