How to place a drop down for the virtual column, in the ruby on rails. The virutal column does not exist in my table , but I want to get the value from the drop down ,when user saves the data.

for example,

product_price is a virtual column , which doesn't exist in my database table. But I would like to have a dropdown, with product price to be displayed from another table. And when user selects the product_price, the selected product_price should be gettable in an object as self.product_price.

Virtual column for labels is working fine, but for drop down its not working for me..any info woud be Thankful...