Thank you very mucho. It was very useful. However, I have a question about how to define columns if we have associations. For instance, my user object has one country, so if I want to see the country name I would do: user.country.name (country is another table). How should I define the columns method for that? I tried: def columns %w(first_name, country.name) end But it's not correct. Thank you very much in advance.