如何使用Ajax和JSON制作下拉菜单？

以下是我用来在OpenCart中显示具有不同级别的类别菜单的代码。它的工作原理，但是在每次单击后，它会产生越来越多的结果，并且有时会通过单击来停止页面：XHR finished loading: POSTXHR finished loading: GET

<script type="text/javascript">
 _url = '';

 $(document).ready(function(){                
    $('#mnav a').on('click', function() {
        var cat = $(this).attr('id');
        _url = '&category_id=' + cat;

        $.post('index.php?route=test/category/child' + _url,
            function(data) {
               if(data.length>10){
                    $('#mnav #sub').remove();
                    $(data).insertAfter($('#mnav #' + cat));
               }
            });
    });
 });

$.ajaxPrefilter(function( options, original_Options, jqXHR ) {
    options.async = true;
});
</script>

代码：

<div id="mnav" class="list-group">
  <?php foreach ($categories as $category) { ?>
  <a id="<?php echo $category['category_id']; ?>" class="list-group-item active"><?php echo $category['name']; ?></a>
  <?php } ?>
</div>

控制器代码：

<?php
class ControllerTestCategory extends Controller {
    public function index() {
        if (isset($this->request->get['path'])) {
            $parts = explode('_', (string)$this->request->get['path']);
        } else {
            $parts = array();
        }

        $data['category_id'] = 0;
        if (isset($parts[0])) {
            $data['category_id'] = $parts[0];
        } else {
            $data['category_id'] = 0;
        }

        if (isset($parts[1])) {
            $data['child_id'] = $parts[1];
        } else {
            $data['child_id'] = 0;
        }

        $this->load->model('catalog/cat');

        $data['categories'] = array();

        $categories = $this->model_catalog_cat->getCategories(0);

        foreach ($categories as $category) {
            $children_data = array();

            $filter_data = array(
                'filter_category_id'  => $category['category_id'],
                'filter_sub_category' => true
            );

            $data['categories'][] = array(
                'category_id' => $category['category_id'],
                'name'        => $category['name'],
                'children'    => $category['children'],
                'products'    => $category['products'],
                'href'        => $this->url->link('product/category', 'path=' . $category['category_id'])
            );
        }

        $this->response->setOutput($this->load->view('test/category', $data));
    }
    public function child() {
        if (isset($this->request->get['category_id'])) {
            $this->load->model('catalog/cat');

            $data['categories'] = array();

            $categories = $this->model_catalog_cat->getCategories($this->request->get['category_id']);

            $data['x'] = '<div id="sub">';

            foreach ($categories as $category) {
                $data['x'] .= '<li>' . $category['name'] . '</li>';
            }
            $data['x'] .= '</div>';
        } else {
            $data['x'] = 'NA';
        }
        $this->response->setOutput($this->load->view('test/category', $data));
    }
}

SQL 代码：

public function getCategories($parent_id = 0) {
    $sql = "SELECT c.category_id, c.parent_id, cd.name,
        (SELECT COUNT(DISTINCT ch.category_id) from category ch where ch.parent_id = c.category_id and cd.language_id = '" . (int)$this->config->get('config_language_id') . "') as children";

    $sql .= " , (SELECT COUNT(DISTINCT p.product_id) 
FROM product p  
    LEFT JOIN product_description pd ON (p.product_id = pd.product_id) 
    LEFT JOIN product_to_category p2c ON (p2c.product_id = p.product_id) 
    LEFT JOIN category_path cp ON (cp.category_id = p2c.category_id) 
WHERE 
    pd.language_id = '" . (int)$this->config->get('config_language_id') . "' AND 
    p.status = '1' AND 
    p.date_available <= NOW()) AS items";

    $sql .= " FROM category c LEFT JOIN category_description cd ON (c.category_id = cd.category_id) WHERE c.parent_id = '" . (int)$parent_id . "' AND cd.language_id = '" . (int)$this->config->get('config_language_id') . "' AND c.status = '1' ORDER BY c.sort_order, LCASE(cd.name)";

    $query = $this->db->query($sql);
    return $query->rows;
}

如果您通过提供所有必要的JavaScript，jQuery和JSON代码来帮助我，我将不胜感激，因为我对这些主题知之甚少：-（