bind function result to dataset/table

I have a table called Products This table contains a number of columns (some boring variables) and an PK column productID. I have writting a function which needs the productID and then calculates the product-rate. So: function getRate (byval productID as integer) as int32 this function is working: getRate(23) delivers the rate of product 23. What I want now is show a datagrid with al the products, some or their properties AND the calculated rate. The solution column.expressions doesn't work because the function was written by myself. Eventually I want to store the value in the database, but first things first. Perhaps my method to solve this is wrong, but please help??

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