问题是我在用户控件里点收藏时，收藏物品的主键是空的
在用TABLE控件显示这个用户控件的时候是正常的，但是在这个用DATALIST控件显示这个用户控件的时候就出问题了。
下面是用户控件的代码：
using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Data.SqlClient;

public partial class productInfo : System.Web.UI.UserControl
{
    SqlConnection con = new SqlConnection(ConfigurationManager.AppSettings["ConnectionString"]);
    private string productID;
    public string ProductID
    {
        set
        {
            this.productID = value.ToString();
        }
    }
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            SqlCommand cmd = new SqlCommand("select * from T_Product_Info where productID='" + productID + "'", con);
            con.Open();
            SqlDataReader sdr=cmd.ExecuteReader();
            sdr.Read();
            this.lblProductName.Text=sdr.GetString(1);
            this.lblMarketPrice.Text=sdr.GetString(2).ToString();
            this.lblOurPrice.Text=sdr.GetString(3).ToString();
            this.hLinkDetails.NavigateUrl = "productDetails.aspx?productID=" + this.productID;
            this.productImage.ImageUrl=sdr.GetString(5).ToString();
        }
    }
    protected void btnBuy_Click(object sender, EventArgs e)
    {
        if (Session["userName"] == null)
        {
            Response.Write("<script>alert('您还没有登录，请登录后再购买，谢谢合作！');location='javascript:history.go(-1)';</script>");
        }
        else
        {
            con.Open();
            string sqlstrProduct = "select count(*) from T_ShoppingCart_Info where productID='" + productID + "'";
            SqlCommand cmdProduct = new SqlCommand(sqlstrProduct, con);
            cmdProduct.ExecuteNonQuery();
            int count = Convert.ToInt32(cmdProduct.ExecuteScalar());
            if (count > 0)
            {
                string sqlstrNum = "select productNum from T_ShoppingCart_Info where productID='" + productID + "'";
                SqlCommand cmdNum = new SqlCommand(sqlstrNum, con);
                int num = Convert.ToInt32(cmdNum.ExecuteScalar());
                num = num + 1;
                string sqlstrAddOne = "update T_ShoppingCart_Info set productNum='" + num + " 'where productID='" + productID + "'";
                SqlCommand cmdAddOne = new SqlCommand(sqlstrAddOne, con);
                cmdAddOne.ExecuteNonQuery();
            }
            else
            {
                string sqlstrShop = "insert into T_ShoppingCart_Info" + "(productID,productName,userName,productNum,ourPrice)"
                    + "values('" + productID + "','"+lblProductName.Text+"','" + Session["userName"] + "', 1 ,'"+lblOurPrice.Text+"' )";
                SqlCommand cmdShop = new SqlCommand(sqlstrShop, con);
                cmdShop.ExecuteNonQuery();
            }
            con.Close();
            Response.Redirect("ShoppingCart.aspx");
        }
    }
[color=FF0000][color=0000FF][color=008080][color=0000FF][color=FF0000]protected void btnCollect_Click(object sender, EventArgs e)
    {
        con.Open();
        if (Session["userName"] == null)
        {
            Response.Write("<script>alert('请先登陆，谢谢！');location='javascript:history.go(-1)';</script>");
        }
        else
        {
            string sqlstrSelect = "select count(*) from T_MyCollection where userName='" + Session["userName"].ToString() + "' and productID='" + productID + "'";
            SqlCommand cmdSelect = new SqlCommand(sqlstrSelect, con);
            int count = Convert.ToInt32(cmdSelect.ExecuteScalar());
            if (count > 0)
            {
                Response.Write("<script>alert('该商品已被收藏！');location='javascript:history.go(-1)';</script>");
            }
            else
            {
                string sqlstrCollection = "insert into T_MyCollection " + " (userName,productID)" + "values('" + Session["userName"].ToString() + "','" + productID + "')";
                SqlCommand cmdCollection = new SqlCommand(sqlstrCollection, con);
                cmdCollection.ExecuteNonQuery();
                Response.Write("<script>alert('收藏成功！');location='javascript:history.go(-1)';</script>");
            }
        }
        con.Close();
        
    }
}[/color][/color][/color][/color][/color]

下面是页面代码：
using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Data.SqlClient;

public partial class showAllHotProducts : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            SqlConnection con = DBCon.createCon();
            SqlCommand cmd = new SqlCommand("select * from T_Product_Info where isHot='是' order by productID Asc", con);
            con.Open();
            SqlDataReader sdr = cmd.ExecuteReader();
            this.DataList1.DataSource = sdr;
            this.DataList1.DataBind();
            sdr.Close();
            con.Close();
        }
    }
}