I ended up going with the running count for karma.  Makes sense for
other reasons too.

On Aug 6, 10:00 pm, kevinpfromnm <[email protected]> wrote:
> It would probably at that.  Might be better to start thinking about
> keeping counts at least cached if not fully handled.
>
> The only thing I worry about is the chance that I or hobo have some
> update calls in place that wouldn't trigger an observer.
>
> I worked out a way to do it with SQL but means I have to add an
> additional layer of SQL for every ratable model.
>
>     raise "Invalid object(s) passed.\n#{user.inspect}\n#
> {category.inspect}" unless
>         user.class == User or category.class == RatingCategory
>     Rating.connection.select_value("SELECT SUM(rating) FROM " +
>       "(SELECT DISTINCT ratings.* FROM ratings,pictures,users where "
> +
>       "(ratable_id = pictures.id AND pictures.user_id = #{user.id}) "
> +
>       "and rating_category_id = #{category.id});").to_i
>
> Unfortunately, select_value doesn't do SQL escaping which is somewhat
> disconcerting.
>
> On Aug 6, 9:32 pm, Bryan M <[email protected]> wrote:
>
> > Why not add two fields to User, num_ratings and avg_rating, and update
> > User with a RatingObserver?
>
> > (I hope I'm not talking out my arse, but I think that would work)
>
> > On Aug 6, 7:46 pm, kevinpfromnm <[email protected]> wrote:
>
> > > Ok, I'll start off with the basic models
> > > Rating
> > >   belongs_to :ratable, :polymorphic => true
>
> > > Picture
> > >   has_many :ratings, :as => :ratable
> > >   belongs_to :user, :creator => true
>
> > > Post
> > >   has_many :ratings, :as => :ratable
> > >   belongs_to :user, :creator => true
>
> > > I'm wanting to be able to give an average for a user for all ratings
> > > applied to their submissions.  There will be additional models in the
> > > future that are ratable as well.
>
> > > So, any ideas on a good way to approach this?  There are a couple of
> > > simple ways but they won't scale.  And this relation will probably be
> > > one of the most pushed that I'll have in the app.  So, I really need a
> > > way to grab the rating for all ratables that belong to a user.  From
> > > my current sense of things looks like I'm going to have to write some
> > > SQL to do it but figured I'd ask anyway in case someone knew of a nice
> > > trick to do sums across polymorphic types.
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