On Sep 28, 2010, at 10:49 AM, Pete wrote:
> Hi,
>
> I am currently a little confused with trying to manipulate a named
> scope that I currently have.
> I use this named scope with a table-plus, and it works very nicely,
> but I want to trim it down a little.
>
> I have two associated models e.g
>
> Catalogue,
>
> has_many :articles
>
> Article:
>
> belongs_to :catalogue
>
> my named scope looks like this (in Class Article)
>
> :finished_articles, { :conditions => [ :finished => true ] }
>
> This works fine on it's own, but I need to trim it to show only the
> most recent finished article per catalogue (based on created_at field)
>
> I have tried to use two named scopes, the other looking like this:
>
> :limited, { :group => "catalogue_id" }
>
> which does only leave one entry per catalogue, but rather than being
> the most recent entry it is the first created.
>
> I just want to be able to reverse this order, but I can't seem to
> figure out how to do this (I have a default order already set, but
> this only seems to affect the scope after it has been rendered..) Also
> setting the order does not seem to have an effect on how the instances
> are gathered from the database.
I think you're going to have to try a different approach - at least in MySQL,
'GROUP BY' doesn't promise anything about fields that vary amongst elements of
the group:
http://dev.mysql.com/doc/refman/5.0/en/group-by-hidden-columns.html
You'll probably be better off doing this in a more Rails-flavored way:
class Catalogue
has_many :articles
has_one :recent_article, :conditions => { :finished => true }, :order =>
'articles.created_at DESC', :class_name => 'Article'
end
Then you could get them all by:
Catalogue.find(:all, :include => :recent_article)
which will eager-load the whole bunch in one go.
This *should* work, but I haven't tried it - and I'm not 100% sure if that
eager-loading trick will work...
--Matt Jones
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