textbox in datalist
 

Hello,
I have a datalist that will be used for online shopping.
I have the product code and next to it a textbox for the user to enter the quantity of the respected product.
By default, I show the product code and the textbox with the value of 1 in it.
What I want to do is to add a linbutton next to the textbox so that, when the user enters a value different than 1 in the textbox, he will clicks on the button in order for me to store the new quantity value.
But how will I know which product's the value the user changed when I have 5 products and I change the quantity value of one of them?