Rails - May 2009 - calculations on a virtual attribute...

I is possible to do calculations on a virtual attribute... such as
sum, or count

I tried using the same as I would on a DB column but of course that
doesn''t work. ie.  Pricelist.sum(:cyberguide)

I have a table with 2 fields, one with a price and the other with a
condition then have a virtual attribute which does a calculation:

  def cyberguide
    if condition <= 2
      [price.pricehigh]
    elsif condition == 3
      [price.pricehigh * 0.9]
    elsif condition == 4
      [price.pricehigh * 0.5]
    elsif condition == 5
      [price.pricehigh * 0.25]
    elsif condition == 6
      [price.pricehigh * 0.2]
    else
      [price.pricehigh * 0.15]
    end
  end

It works perfectly for individual functions, but how would a sum the
virtual attribute?

Thanks

On May 3, 7:55 am, holden
<holden.tho...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> I is possible to do calculations on a virtual attribute... such as
> sum, or count
>
> I tried using the same as I would on a DB column but of course that
> doesn''t work. ie.  Pricelist.sum(:cyberguide)
>
You''re going to have to construct an appropriate sql fragment, eg
according to the docs you can do Pricelist.sum("2 * price") - you just
need that on steroids.


Fred



> I have a table with 2 fields, one with a price and the other with a
> condition then have a virtual attribute which does a calculation:
>
>   def cyberguide
>     if condition <= 2
>       [price.pricehigh]
>     elsif condition == 3
>       [price.pricehigh * 0.9]
>     elsif condition == 4
>       [price.pricehigh * 0.5]
>     elsif condition == 5
>       [price.pricehigh * 0.25]
>     elsif condition == 6
>       [price.pricehigh * 0.2]
>     else
>       [price.pricehigh * 0.15]
>     end
>   end
>
> It works perfectly for individual functions, but how would a sum the
> virtual attribute?
>
> Thanks