插入PHP和mysql复选框

我正在研究一个项目，我需要将多个复选框和文本框的值(从产品列表)传递到数据库上的表(new_orders)。

我设法创建了从表articles中检索产品的列表，但是我不能将我选择的产品与我在数据库上的表new_orders中插入的数量插入。

代码如下:

foreach($A_result as $key => $value) // για χρηση όλων των αντικειμένων του πίνακα A_apotelesma
{

// shows al the products
    echo "<tr> 
              <td align=center>".$j++."</td>
              <td align=center>".$value['name']."</td>
              <td align=center>".$value['price']."</td> ";
echo"<td> // each product has a checkbox and a text box to enter the quantity
            <input type=checkbox name='"article[]'"></input>
            <input type=text name='quantity_".$value['id_article']."' size='3' maxlength='2'>
         </td>";
    echo"<td><input type='hidden' name='id_article' value=".$value['id_article']."></td>"; 
    echo"<td><input type='hidden' name='"code_user'" value='"code_user'"></td>"; 
    echo"</tr>";
}
}
?>  
 // The form above redirects to the insert_order.php page:

<?php
include("conn.php");
session_start();
$checkbx=$_POST['article'];
if($_POST['article']){
for($i=0;$i<sizeof($checkbx);$i++){
$quantity=$_POST['quantity_.$id_article'];
$username=$_SESSION['logged_user_username'];
$insert_order_query= "INSERT INTO new_orders (id_article, quantity, username) VALUES (".$id_article.",".$quantity.", '".$username."')";
//echo $insert_order_query;
$insert_order=mysql_query($insert_order_query) or die('Error,query failed!!'); 
 if ($insert_order)
     echo '<script language="javascript">alert("New order created!"); document.location="logged_in_user.php?menu=1";</script>';
 else
 {
    echo '<script language="javascript">alert("The order has not been created.")</script>';
    echo '<script language="javascript"> document.location="logged_in_user.php?menu=1.php"; </script>';
    exit();
 }
}
}
?>

我总是得到错误信息