EC-CUBEでAjax

EC-CUBE (v2.13.5)
PHP (v5.6.10)

サンプルとして
セレクトボックス変更で複数のセレクトボックスの選択肢をかえる場合

Smartyはよく分からんので
分かればもっと綺麗になるやもしれんね

sample.tpl

<script type="text/javascript">
$(function($) {
    $('select[name=A]').change(function() {
        $.ajax({
            type: "POST",
            url:  "/ajax/index.php",
            data: {value:$(this).val()},
            dataType: "json",
            success: function(r) {
                //console.log(r);
                $.each(r, function(k, v) {
                    var $select = $("select[name="+k+"]");
                    $select.text("");
                    $.each(v, function(k2, v2) {
                        $select.append("<option value=\""+v2['id']+"\">"+v2['name']+"</option>");
                    })
                })
            },
            error: function(){
            }
        });
    });
});
</script>

<select name="A">
<option value="1">A1<option>
<option value="2">A2<option>
<option value="3">A3<option>
</select>


<select name="B">
<option value="">-<option>
</select>

<select name="C">
<option value="">-<option>
</select>

/html/ajax/index.php

<?php
require_once '../require.php';
require_once CLASS_REALDIR . 'pages/ajax/LC_Page_Ajax.php';
$objPage = new LC_Page_Ajax();
$objPage->init();
$objPage->process();

/data/class/pages/ajax/LC_Page_Ajax.php

<?php
class LC_Page_Ajax {

    public function init() {}

    public function process() {
        $this->action();
    }

    public function action() {
        $data = self::sample();
        @header('Content-Type: application/json; charset=utf-8');
        echo json_encode($data);
        return;
    }

    public function sample() {
        $value = $_POST['value'];
        $relations = ['B', 'C'];

        $query = new SC_Query();
        foreach ($relations as $r) {
            $cols = "id, name";
            $from = "**table**";
            $where = "**where**";
            $data[$r] = $query->select($cols, $from, $where);
        }
        return $data;
    }

}

セキュリティ云々は各々追記してください。