filtering the products on the bases of catagory

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C#

ASP.NET

i have some catagoriens in a grid view.. which are shown in hyperlinks..

e.g i have mouse, keyboards e.t.c in catorgiries shown in gridview. when i click on any catagory lets say mouses.. the page will redirct to productcatalog.aspx page showing the mouse of all the brands available..

but the problem is that. its not filtering the products from the mouse catagory.. but showing all the proucts in the database. this is the code iam writing..

<asp:HyperLinkField DataNavigateUrlFields="CategoryID" 
                    DataNavigateUrlFormatString="~/ProductCatalog.aspx?CategoryID={0}" 
                    DataTextField="CategoryName" HeaderText="Categories" />

now on productcatalog.aspx page how i can filter the products on the bases of querystring