Question

When I use a column alias in a query with find_by_sql, it doesn’t appear to be set in the result objects, even when I add an attr_accessor for the property.

class Country < ActiveRecord::Base

  attr_accessor :average_score

  def self.sorted_by_average_score
    sql = "SELECT country_id, AVG(score) AS average_score, countries.name " +
    "FROM players " +
    "INNER JOIN countries ON players.country_id = countries.id " +
    "GROUP BY country_id "
    Country.find_by_sql(sql)
  end
end

I would expect to be able to do this:

countries = Country.sorted_by_average_score.first.average_score

…but it always returns nil, even though a value is definitely returned from the query.

Can anyone explain to me why the attribute isn’t set in the object?

Answer 1

You don’t need to use attr_accessor, see neutrino’s explanation. You just need to access your virtual column by using the attributes hash. This question is the same as Rails: find_by_sql and virtual column. Sample code for your example:

countries = Country.sorted_by_average_score.first.attributes['average_score']