将mysql查询结果存储在codeigniter中的会话中

Question

这是我在控制器中的代码......

function get_product(){
        $purchase_id=$_POST['purchase_id'];
        if($purchase_id!=''){
        //$post_array['cart']='';
        $res = $this->db->query("select * from phppos_productdetails WHERE
  purchase_id='$purchase_id'");
        ?>
        <tr>
<th>Product  Name</th>
<th>Quantity </th>
<th>Unit </th>
<th>Unit Rate</th>
<th>Action</th>
</tr>
        <?php
 $i=0;
        foreach($res->result() as $row )
        {
            $sess_products[$i]['product_id'] = $row->product_id;
        $sess_products[$i]['quantity'] = $row->quantity;
        $sess_products[$i]['unit'] = $row->unit;
        $sess_products[$i]['unit_rate'] = $row->unit_rate;

        $this->session->set_userdata('sess_products',$sess_products);

        $query = $this->db->query("SELECT product_name FROM phppos_product WHERE 
  product_id='".$row->product_id."'");
    foreach ($query->result() as $row1 )
{
$product_name=$row1->product_name;

}
    echo "<tr>";
    echo "<td>".$product_name."</td>";
    echo "<td>".$row->quantity."</td>";
    echo "<td>".$row->unit."</td>";
    echo "<td>".$row->unit_rate."</td>";
    echo "<td><a href='javascript:void(0)' rownum='".$i."' class='remove_from_cart'><img src='images/close.png'/></a></td>";
    echo "</tr>";
    $i++;

        }


    }
}

这是由ajax调用调用的控制器中的函数。那么如何将该查询结果存储在codeigniter ??

中的会话数组中

我正在接受这样的

 $demo_arr['cart']= $this->session->userdata('sess_products');