Reportable Concern

reportable.rb

module Reportable
  extend ActiveSupport::Concern

  module ClassMethods
    # Chain on a scope and specify the fields to extract.
    # Example:
    #   User.enabled.report %{
    #     :email_opt_in,
    #     'created_at as sign_up_date'
    #   }
    #
    #   => JSON string [{email_opt_in: true, created_at: "timestamp"}]
    #
    def report(*fields)
      select(*fields).pg_json
    end

    def pg_json
      connection.execute(%{
        select array_to_json(array_agg(row_to_json(t))) as result
        from (#{all.to_sql}) t
      })[0]["result"] || []
    end
  end
end

I created this to spit out raw (or simple processing by postgresql) data to be used by d3 in a page. Skips ActiveRecord and Ruby JSON generation. PG does the json building from the query.

Since they're class methods, you can chain it onto any scope you want.