我的控制器代码
<?php
if (!defined('BASEPATH'))
    exit('No direct script access allowed');
class Welcome extends CI_Controller {
    public function __construct() {
        parent::__construct();
        $this->load->model('welcome_model');
    }
    public function index() {
        $data = array();
        $data['category'] = $this->welcome_model->select_category();
        $data['product'] = $this->welcome_model->select_product();
        $this->load->view('purchase_entry', $data);
    }
    function get_products($category) {
        header('Content-Type: application/x-json; charset=utf-8');
        echo(json_encode($this->welcome_model->select_product_by_category($category)));
    }
    public function add() {
        $result = $this->welcome_model->select_product_by_id($this->input->post('product_id', TRUE));
        $insert = array(
            'id' => $this->input->post('product_id', true),
            'qty' => $this->input->post('quantity', true),
            'price' => $this->input->post('unit_price', true),
            'name' => $result->product_name
        );
        $this->cart->insert($insert);
        redirect("welcome/index");
    }
}
我的模型课
<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');
class Welcome_Model extends CI_Model {
    public function select_category()
    {
        $this->db->select('*');
        $this->db->from('category');
        $query_result=  $this->db->get();
        $result=$query_result->result();
        return $result;
    }
    public function select_product()
    {
        $this->db->select('*');
        $this->db->from('product');
        $query_result=  $this->db->get();
        $result=$query_result->result();
        return $result;
    }
    public function select_product_by_category($category_id)
    {
        $this->db->select('*');
        $this->db->from('product');
        $this->db->where('category_id',$category_id);
        $query_result=  $this->db->get();
        $result=$query_result->result();
        return $result;
    }
    public function select_product_by_id($product_id)
    {
        $this->db->select('*');
        $this->db->from('product');
        $this->db->where('product_id',$product_id);
        $query_result=  $this->db->get();
        $result=$query_result->row();
        return $result;
    }
}
?>
我的视图文件是
<html>
<head>
    <title></title>
    <script type="text/javascript" src="<?php echo base_url(); ?>js/jquery-1.7.1.min.js"></script>
    <script>   
        $(document).ready(function(){
            $('#category_id').change(function(){ 
                $("#product_id > option").remove(); 
                var category_id = $('#category_id').val();
                $.ajax({
                    type: "POST",
                    url: "http://localhost/test_cart/index.php/welcome/get_products/"+category_id, 
                    success: function(cities) 
                    {
                        $.each(cities,function(id,name) 
                        {
                            var opt = $('<option />'); 
                            opt.val(id.product_id);
                            opt.text(name.product_name);
                            $('#product_id').append(opt); 
                        });
                    }
                });
            });
        });
    </script>
    <style type="text/css">
        a{text-decoration: none;}
    </style>
</head>
<body>
    <form action="<?php echo base_url(); ?>welcome/add" method="post">
        <table width="400px" align="center">
            <caption><h3>Purchase Invoice</h3></caption>
            <tr>
                <td>Invoice Date :</td>
                <td>
                    <input type="text" name="invoice_date" value=""/>
                </td>
            </tr>
            <tr>
                <td>Select Category :</td>
                <td>
                    <select name="category_id" id="category_id">
                        <option>--- Select Category ---</option>
                        <?php foreach ($category as $aCategory) { ?>
                            <option value="<?php echo $aCategory->category_id; ?>"><?php echo $aCategory->category_name; ?></option>
                        <?php } ?>
                    </select>
                </td>
            </tr>
            <tr>
                <td>Select Product :</td>
                <td>
                    <select name="product_id" id="product_id">
                        <option>--- Select Product ---</option>
                    </select>
                </td>
            </tr>
            <tr>
                <td>Unit Price :</td>
                <td>
                    <input type="text" name="unit_price" value=""/>
                </td>
            </tr>
            <tr>
                <td>Quantity :</td>
                <td>
                    <input type="text" name="quantity" value=""/>
                </td>
            </tr>
            <tr>
                <td> </td>
                <td>
                    <input type="submit" value="Submit"/>
                </td>
            </tr>
        </table>
    </form>
    <form action="" method="post">
    <h2 align="center">Invoice Details</h2>
    <table border="1px" cellpadding="5px" cellspacing="1px" style="margin-top:10px;border-collapse:collapse" width="500px" align="center">
        <tr align="center" style="font-family:Arial, Helvetica, sans-serif; font-size:12px;">
            <th>Serial</th>
            <th>Product Name</th>
            <th>Quantity</th>
            <th>Unit Price</th>
            <th>Amount</th>
            <th>Action</th>
        </tr>
        <?php if ($cart = $this->cart->contents())  ?>
        <?php
        $i = 1;
        foreach ($cart as $item) {
            ?>
            <tr>
                <td><?php echo $i++; ?></td>
                <td><?php echo $item['name']; ?></td>
                <td><?php echo $item['qty']; ?></td>
                <td><?php echo $item['price']; ?></td>
                <td><?php echo $item['subtotal']; ?></td>
                <td>
                    <a href="">Update</a> | <a href="">Remove</a>
                </td>
            </tr>
        <?php } ?>
    </table>
    </form>
</body>
我的问题是,当我想将产品添加到购物车时,控制器的 add 方法无法从帖子中找到参数我的意思是 product_id 没有从视图值传递。如何将选项值从视图传递到控制器作为参数?