def follow_path( steps, past_steps = [] )
      if steps.is_a?( Hash )
        steps.each do |step, next_steps|
          path_to_this_point = [past_steps, step].flatten
          reflection = reflection_for( path_to_this_point ) rescue nil
          if reflection
            follow_path( next_steps, path_to_this_point )
          else
            follow_comparison( next_steps, past_steps, step )
          end
        end
      elsif steps.is_a?( Array ) && steps.length == 2
        if reflection_for( past_steps )
          follow_comparison( steps, past_steps, :id )
        else
          follow_comparison( steps, past_steps[0..-2], past_steps[-1] )
        end
      else
        raise "invalid obligation path #{[past_steps, steps].inspect}"
      end
    end
def follow_path( steps, past_steps = [] )
      if steps.is_a?( Hash )
        steps.each do |step, next_steps|
          path_to_this_point = [past_steps, step].flatten
          reflection = reflection_for( path_to_this_point ) rescue nil
          if reflection
            follow_path( next_steps, path_to_this_point )
          else
            follow_comparison( next_steps, past_steps, step )
          end
        end
      elsif steps.is_a?( Array ) && steps.length == 2
        if reflection_for( past_steps )
          follow_comparison( steps, past_steps, :id )
        else
          follow_comparison( steps, past_steps[0..-2], past_steps[-1] )
        end
      else
        raise "invalid obligation path #{[past_steps, steps].inspect}"
      end
    end
Parses the next step in the association path.  If it's an association, we advance down the
 path.  Otherwise, it's an attribute, and we need to evaluate it as a comparison operation.