Rails - Oct 2005 - hand writing sql for eager loading of thumbnails

Can anyone point me to a resource for hand coding some sql so I can create my 
own for the following models:

I''m using single table inheritance to store related objects eg:

Thumbnail < Image < File :: ActiveRecord:Base

Image 
has_many thumbnails

Thumbnail 
has_one image

When I come to list thumbnails I''d like to be able to:
1. List all images relating to a product
2. For each Image get a link to the smallest thumbnail 64px x 64px and link to 
it.
3. List all thumbnails related to an image

I figure I need to 3 things:
1. Select images related to a product
2. JOIN my each image to it''s related small thumbnail giving me
something like:
image.thumbnail_url
3. JOIN all thumbnails to their related images so I can use @image.thumbnails

Other wise I''m running N+1 queries to try and achieve a similar result.
I''ll
take any advice, even if it''s that I''m going about this
completely the wrong
way!

Cheers,

Graham

Hi !

2005/10/18, Graham <g.arrowsmith@gmail.com>:
> Can anyone point me to a resource for hand coding some sql so I can create
my
> own for the following models:
Have you investigated the :include option of find ?  Basically, when
you find an object, you can preload selected relationships.  You'd use
it like this:

images = Image.find(:all, :conditions => [...], :include => :thumbnail)
images.each do |img|
  img.thumbnail.url
end

Hope that helps !
François

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Francois Beausoleil <francois.beausoleil@...>
writes:
> 
> images = Image.find(:all, :conditions => [...], :include =>
:thumbnail)
> images.each do |img|
>   img.thumbnail.url
> end
> 
> Hope that helps !
> François
> 
Hi François,

I''m afraid the :include won''t work as :thumbnail and :image
share the same
table (single table inheritance) - as they''re identical and made sense
to
use one table. 

DHH made reference to this in a previous post:
It’s currently not possible to use eager loading on multiple associations 
from the same table.
http://api.rubyonrails.com/classes/ActiveRecord/Associations/ClassMethods.html

So I''m trying to write the sql myself. (Trying as opposed to
succeeding...)

> DHH made reference to this in a previous post:
> It''s currently not possible to use eager loading on multiple
associations
> from the same table.
>
http://api.rubyonrails.com/classes/ActiveRecord/Associations/ClassMethods.html
>
> So I''m trying to write the sql myself. (Trying as opposed to
succeeding...)
You could try the current patch that does this, which is in ticket
2172.  It was marked for inclusion for 1.0 until this past weekend. 
Unfortunately, it was decided that the patch wasn''t 1.0 ready. No
reason was given, but my guess is that this is because the patch is
large, affects all the database adapters, and affects numerous other
areas in addition to multiple associations on the same table.  The
earlier patch (in ticket 1562) that just implements support for
multiple associations from the same table was closed as wontfix
because it was combined into a later patch in 2172.  Instead of just
applying the patch in 1562 (and waiting until later to apply the other
improvements in 2172), the decision was made to release 1.0 without
the functionality.

Disclaimer: I wrote most of the code to support multiple associations
on the same table, and it''s certainly possible that it was that code
that wasn''t ready for 1.0 (again, no reason was given, so I
don''t
know).