Rails - Dec 2008 - Association to return only the first of an associated list

A little background: in our schema, Resource has_many :assets, through a
join table called items.

Whenever we show a resource, we also show a thumbnail for its first
associated asset.  Currently, this means that we''re doing a lot of sql
action in the view: for example, a partial like this might be repeated
100 times:

....
<% asset = resource.assets.first %>
<%= image_tag asset.name, asset.path %>
...

Obviously doing loads of little queries in the view isn''t good:  what
i''d like to do is somehow eager-load that first asset with the include
option.  We tried making a method called ''primary_asset'' which
returns
the first asset for a resource, but that can''t be "include"d:
i think
that in order to include it i need to set it up as an association.
Which leads me to my actual question:  how do i set up a has_one
association to return only the first asset from the collection of
associated assets?

has_one doesn''t seem to have an ''sql'' option,
otherwise i''d just do
something like

  has_one :primary_asset, :class_name => "Asset", :sql =>
"SELECT
assets.* FROM assets INNER JOIN items ON assets.id = items.asset_id
WHERE ((items.resource_id = #{id})) ORDER BY position LIMIT 1"

Can anyone see how i can set this up?  I''m using rails 2.0.2.

thanks, max
-- 
Posted via http://www.ruby-forum.com/.

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en
-~----------~----~----~----~------~----~------~--~---

Have you tried

has_one :primary_asset, :class_name=>"Asset",
:order=>"position"


On Dec 8, 4:59 am, Max Williams
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:
> A little background: in our schema, Resource has_many :assets, through a
> join table called items.
>
> Whenever we show a resource, we also show a thumbnail for its first
> associated asset.  Currently, this means that we''re doing a lot of
sql
> action in the view: for example, a partial like this might be repeated
> 100 times:
>
> ....
> <% asset = resource.assets.first %>
> <%= image_tag asset.name, asset.path %>
> ...
>
> Obviously doing loads of little queries in the view isn''t good:
 what
> i''d like to do is somehow eager-load that first asset with the
include
> option.  We tried making a method called ''primary_asset''
which returns
> the first asset for a resource, but that can''t be
"include"d:  i think
> that in order to include it i need to set it up as an association.
> Which leads me to my actual question:  how do i set up a has_one
> association to return only the first asset from the collection of
> associated assets?
>
> has_one doesn''t seem to have an ''sql'' option,
otherwise i''d just do
> something like
>
>   has_one :primary_asset, :class_name => "Asset", :sql =>
"SELECT
> assets.* FROM assets INNER JOIN items ON assets.id = items.asset_id
> WHERE ((items.resource_id = #{id})) ORDER BY position LIMIT 1"
>
> Can anyone see how i can set this up?  I''m using rails 2.0.2.
>
> thanks, max
> --
> Posted viahttp://www.ruby-forum.com/.
--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en
-~----------~----~----~----~------~----~------~--~---