activerecord - how to modify complex find_by_sql query w/ union into rails 3 -

here's current query:

@feed = ratedactivity.find_by_sql(["(select *, null queue_id, 3 model_table_type rated_activities user_id in (?)) " +   "union (select *, null queue_id, null rating, 2 model_table_type watched_activities user_id in (?)) " +   "union (select *, null rating, 1 model_table_type queued_activities user_id in (?)) " +"order activity_datetime desc limit 100", friend_ids, friend_ids, friend_ids]) 

now, bit of kludge, since there models set for:

class ratedactivity < activerecord::base   belongs_to :user   belongs_to :media end  class queuedactivity < activerecord::base   belongs_to :user   belongs_to :media end  class watchedactivity < activerecord::base   belongs_to :user   belongs_to :media end 

would love know how use activerecord in rails 3.0 achieve same thing done crazy union have there.

it sounds should consolidate these 3 separate models single model. statuses such "watched", "queued", or "rated" implicit based on attributes of model.

class activity < activerecord::base   belongs_to :user   belongs_to :media    scope :for_users, lambda { |u|     where("user_id in (?)", u)   }   scope :rated, where("rating not null")   scope :queued, where("queue_id not null")   scope :watched, where("watched not null") end 

then, can call activity.for_users(friend_ids) 3 groups trying accomplish above... or can call activity.for_users(friend_ids).rated (or queued or watched) 1 group. way, of activity logic consolidated in 1 place. queries become simpler (and more efficient) , don't have maintain 3 different models.