How do I check a not-null query string against a sql database in c# for ASP.NET? - asp.net

Question

I have a web page that is pulling information about a specific database entry based on the reference number of that database entry. This reference number is not the SQL ID number, but a number that we assign at entry time.
This reference number is passed to the page in the form of a query string, and as long as the reference number actually exists in the database, everything is fine. However, if the reference number does not exist, my details page comes up blank: no exception or anything.
I'm not sure how relevant sharing my code is in this case, but I'll play it safe:
protected void Page_Load(object sender, EventArgs e)
{
using (KidsEntities detailEntities = new KidsEntities())
{
string imgPath = ConfigurationManager.AppSettings["imagePath"];
string KidNum = Request.QueryString["ChildNum"].ToString();
var KidSpecific = from Kid in detailEntities.Kids
where Kid.Number == KidNum
... ;
DescRepeater.DataSource = KidSpecific.ToList();
DescRepeater.DataBind();
}
}
I can put in a redirect in case some joker tries to bring up my details page without going through the main directory (which would bring up a null query string), but if used correctly, my query string will never be null or empty. What I'm trying to prepare for is if someone bookmarks my details page with a query string that was valid at the time of bookmarking, but then gets taken down.
How can I check to make sure there is a reference number in the database that matches the query string before the var "KidSpecific" fires? If there is no such reference number, I need to be able to use a Response.Redirect to put up an error page instead of the blank screen that shows now.
Thanks in advance for any help.

Answer 1

Why do you need to do your check before the query fires? You'll have to check the database for the entry either way. Try redirecting if your query comes up empty:
protected void Page_Load(object sender, EventArgs e)
{
using (KidsEntities detailEntities = new KidsEntities())
{
string imgPath = ConfigurationManager.AppSettings["imagePath"];
string KidNum = Request.QueryString["ChildNum"].ToString();
var KidSpecific = from Kid in detailEntities.Kids
where Kid.Number == KidNum
... ;
var KidSpecificList = KidSpecific.ToList();
//Redirect if there are no results!
if (KidSpecificList.Count() < 1)
Response.Redirect("RedirectPage.aspx");
DescRepeater.DataSource = KidSpecificList;
DescRepeater.DataBind();
}
}

Answer 2

You can check quety string with string.IsNullOrEmpty like this:
protected void Page_Load(object sender, EventArgs e)
{
using (KidsEntities detailEntities = new KidsEntities())
{
string imgPath = ConfigurationManager.AppSettings["imagePath"];
string KidNum = Request.QueryString["ChildNum"].ToString();
if ( string.IsNullOrEmpty ( KidNum ) ) {
Response.Redirect ( "WhatEverURI" );
} else {
var KidSpecific = from Kid in detailEntities.Kids
where Kid.Number == KidNum
... ;
DescRepeater.DataSource = KidSpecific.ToList();
DescRepeater.DataBind();
}
}
}