I'm developing a system similar to the ForumExample (http:// wiki.rubyonrails.org/rails/pages/ForumExample), and stumbled upon the following.
Let's say I wanted to get all the categories a certain user posted in. How do I get that information withouth using a custom query through :finder_sql (and thus losing the find_in_collection ownage)? It would also be great to see how many post that author made in a category while I'm at it.
Not tested, not sure if it works, but an idea:
#Controller @categories = Category.find :all, :conditions => "(messages.author_id = 1 AND categories.id = 1", :include => { :forums => { :topics => replies } }
#view <% @categories.each do |c| posts = 0 topics = 0 topics = c.forums.inject do |tsum,topic| tsum += 1 #count and sum up all topics user has created. posts += topic.inject do { |psum,post| psum += 1 } #count and sum up all posts of the user in each topic end end %> <%= "#{@user.id} has started #{topics} Topics and #{posts} in Category #{c.name}" %><br />
<% end %>
not sure if i use inject correctly here, just googled this thing 
Hope oyu get the idea.
and you should put thta stuff in a helper i guess, to make it less
clumpsy.
Eager loading would be the answer: Category.find(:all, :include=>[{:forums=>{:messages=>:author}}], :conditions=>['authors.name= ?', 'Robert']) I'm not sure this needs corrections or not but the trick is that curly braces in :include gives you nested joins.
Charly
The find() works (although I must rather would like to have a thing like this in the model).
Counting the posts is still a problem. An each() loop isn't that scalable. Any thoughts on doing a SUM in the SQL query somewhere or something? I've tried out a couple of things with :select, but it was just ignored...