build_from

# File activerecord/lib/active_record/relation/query_methods.rb, line 913
    def build_from
      opts, name = from_value
      case opts
      when Relation
        name ||= 'subquery'
        self.bind_values = opts.bind_values + self.bind_values
        opts.arel.as(name.to_s)
      else
        opts
      end
    end