Gridview Problem...Pls...

Question

I m doing Invoice Project For My student..

When customer buying 3 kinds of products (pencils,bags,Cd’s), I saved  these records in 3 rows with Unique Customer Id..Now my Inovice Table having 3 rows for 1 Customer..No problem upto this stage..

My Invoice table having the following columns..                InvoiceId,CustomerID,ProductName,ProductPrice,Quantity,Total,InvoiceAmount.

When I going to update this Invoice I have some problem..so I post here..

I shows those 3 rocords in gridview with autoedit,delete buttons =true…

In Gridview I shows , 1^st column is ProductName,2^nd column is Quantity, 3^rd Column in Price, 4^th Column in Total Amount..

I used template columns in my gridview….when I click any row of edit button  I want to show ProductNames in DropDownlist(normally it comes with text box..i don’t want textbox),then If I select any productname from 1^st column of dropdownlist , the corresponding product price will be coming in 3^rd column of Price TextBox and if I change quantity in my 2^nd column of Textbox , the total amount(quantity *Price=totalamt) will be calculated and display in 4^th column of Text box..finally when I click update button , the update value will be stored in database..all the works with in the gridview control…