在模型中添加语法“where”，但未选中（datatables ajax codeigniter）

[Datatables joining tables search and order stuck with codeigniter

the case is the same at this link, see the correct answer, but why can't it be given "where"?

private function _get_datatables_query($term=''){ //term is value of $_REQUEST['search']['value']
    $column = array('k.id_kota','k.nm_kota', 'p.nm_propinsi');
    $this->db->select('k.id_kota, k.nm_kota, p.nm_propinsi');
    $this->db->from('kota as k');
    $this->db->where('k.id_kota',2); //this problem
    $this->db->join('propinsi as p', 'p.id_propinsi = k.id_propinsi','left');
    $this->db->like('k.id_kota', $term);
    $this->db->or_like('k.nm_kota', $term);
    $this->db->or_like('p.nm_propinsi', $term);
    if(isset($_REQUEST['order'])) // here order processing
    {
       $this->db->order_by($column[$_REQUEST['order']['0']['column']], $_REQUEST['order']['0']['dir']);
    } 
    else if(isset($this->order))
    {
       $order = $this->order;
       $this->db->order_by(key($order), $order[key($order)]);
    }
}

I will showing all data basic id.kota = 2 but can't. Please help. Thanks