get readonlyGrid Fv! data outside gridcolumn()

Hi,

I have the following scenario:

Take a shopping cart. I have three tables: cartdetails which has foreign key productsId from product table, product table  which has categoryId from category table.

the grid data is -> cartdetails and columns are ->   srno| category name| category type| category data| productname| product price| product data| quantity| totalprice

Now in the grid i can call a rule to fetch the required data as:

1. call getcategorydata()-> for  category name| category type| category data

2. call getproductdata()-> for productname| product price| product data

Instead of calling the rule again and again for the three columns each, i want to call it once per row. So im trying to use localvariables. 

But the data that i can use is only fv!currentpage outside the gridcolumn() . so i tried doing fv!currentpage.data.productid. This is giving me the whole array of products. I want to index this to only get the individual row's productid.

Idk if i explained it properly, 

Thank youin advance