Dynamic Combobox with Codeigniter 3

The basic idea is similar to the combobox of states and cities , that when selecting a state, the next select returns the referring cities.

In my case I can not list these fields in the second select (which would be equivalent to cities).

With the following codes, the only occurrence is that, by selecting any of the fields, the second select receives an option with the name of 'choice', according to the JS reset script.

I tried the CustomFileList method and it is returning the data correctly, the problem is in the asynchronous transition.

Note: The code is based on this article .

Obs2: I know that in the option I put the value 'test' ..

Here are code snippets:

Copywriting

defined('BASEPATH') OR exit('No direct script access allowed');

class Redacoes extends CI_Controller {

function __construct() {
    parent::__construct();
}

public function index() {
    //Carregar o model
    $this->load->model('Read_model');

    $data['redacoes'] = $this->Read_model->ListaRedacoes('Matricula', 'asc');

    if ($this->input->post('frmFiltro')):
        $data['filtros'] = $this->Read_model->listaFiltroPersonalizado($this->input->post('frmFiltro'));
    endif;

    $this->template->load('base', 'home', $data);
}
}

Read (Model)

class Read_model extends CI_Model {

private $table = 'redacoes';

public function __construct() {
    parent::__construct();
}

function ListaRedacoes($sort = 'Data', $order = 'desc', $limit = null, $offset = null) {

    $this->db->order_by($sort, $order);

    if ($limit):
        $this->db->limit($limit, $offset);
    endif;

    $query = $this->db->get($this->table);
    return $query->result();
}

public function ListaFiltroPersonalizado($filtro) {
    $this->db->select($filtro);
    $this->db->join('aluno_2016', 'aluno_2016.matricula_aluno = redacoes.Matricula');
    $this->db->group_by($filtro);
    $this->db->order_by($filtro, 'asc');
    $query = $this->db->get($this->table);
    return $query->result();
}

public function FiltraRedacoes($campo, $filtro) {
    $this->db->join('aluno_2016', 'aluno_2016.matricula_aluno = redacoes.Matricula');
    $this->db->where($campo, $filtro);
    $query = $this->db->get($this->table);
}
}

home (view)

<form method="post">
    <div class="form-group">
        <div class="input-group">
            <label class="input-group-addon"><i class="fa fa-search"></i></label>
            <select name="frmFiltro"  id="frmFiltroPersonalizado" class="form-control" required="required">
                <!--onchange="this.form.submit()"-->
                <option value="" selected>-- Selecione um filtro --</option> 
                <option value="Tipo">Tipo</option> 
                <option value="unidade_aluno">Unidade</option>
                <option value="periodo_aluno">Período</option>  
                <option value="nome_curso">Curso</option>  
                <option value="turma_aluno">Turma</option>  
                <option value="sala_aluno">Sala</option>  
                <option value="descricao_curso">Descricao curso</option>  
            </select>
        </div>
    </div>
    <div class="form-group">
        <div class="input-group">
            <label class="input-group-addon"><i class="fa fa-search"></i></label>
            <select name="frmFiltroValor" id="frmFiltroPersonalizadoValor" class="form-control" requireds="required">
                <option value="" selected>-- Selecione --</option> 

                <?php foreach ($filtros as $filtro): ?>
                    <option value="">teste</option>
                <?php endforeach; ?>

            </select>
        </div>                                        
    </div>

    <div class="form-group">
        <input class="btn btn-primary" type="submit">
    </div>
</form>

Javascript (Ajax)

var path = '<?= base_url(); ?>'
            $(function () {

                $("select[name=frmFiltro]").change(function () {

                    filtro = $(this).val();

                    if (filtro === '')
                        return false;

                    resetaCombo('frmFiltroValor');

                    $.getJSON(path + 'redacoes/filtro/' + filtro, function (data) {

                        var option = new Array();

                        $.each(data, function (i, obj) {

                            option[i] = document.createElement('option');
                            $(option[i]).attr({value: obj.id});
                            $(option[i]).append(obj.nome);

                                $("select[name='frmFiltroValor']").append(option[i]);

                            });

                        });

                    });

                });

                function resetaCombo(el) {
                    $("select[name='" + el + "']").empty();
                    var option = document.createElement('option');
                    $(option).attr({value: ''});
                    $(option).append('Escolha');
                    $("select[name='" + el + "']").append(option);
                }

.htacess

RewriteEngine on
RewriteCond $1 !^(index\.php|assets|robots\.txt)
RewriteRule ^(.*)$ index.php/$1 [L]