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    <p>What you're looking for is a <a href="http://api.rubyonrails.org/classes/ActiveRecord/NamedScope/ClassMethods.html" rel="nofollow noreferrer">named scope</a> in the Forum model.</p> <p>The join can be greatly simplified by adding has_many :through relationships for your Comment and Reply models in the Forum model. But I can never remember how nested joins work out, so I've posted a solution that will work with what you've got.</p> <pre><code>class Forum &lt; ActiveRecord::Base has_many :topics, :dependent =&gt; :destroy, :order =&gt; 'created_at desc' named_scope :user_posted, lambda {|user| { :joins =&gt; "JOIN topics t ON t.forum_id = forums.id " + "JOIN comments c ON c.topic_id = t.id " + "JOIN replies r ON r.comment_id = c.id", :conditions =&gt; ["t.user_id = ? OR c.user_id = ? OR r.user_id = ?", user, user, user], :group =&gt; "forums.id" } } end </code></pre> <p>Now...</p> <pre><code>Forum.user_posted(@user) </code></pre> <p>Will return an array of forums where a user has posted a topic, reply or comment.</p> <p>For a list of forums a particular user has posted in:</p> <pre><code>class User &lt; ActiveRecord::Base has_many :topics, :dependent =&gt; :destroy has_many :comments, :dependent =&gt; :destroy has_many :replies, :dependent =&gt; :destroy named_scope :posted_in_forum, lambda {|forum| { :joins =&gt; "JOIN replies r ON r.user_id = users.id "+ "JOIN comments c ON c.user_id = users.id OR c.id = r.comment_id " + "JOIN topics t ON t.user_id = users.id OR t.id = c.topic_id " + "JOIN forums f ON t.forum_id = forums.id ", :conditions =&gt; ["f.id = ?", forum], :group =&gt; "users.id" } } end </code></pre> <p>Assuming I got that right, this statement:</p> <pre><code>User.posted_in_forum(@forum) </code></pre> <p>will return a list of users that have posted in forum either by topic, comment or reply.</p> <p>P.S. it's probably not a good idea to allow destruction of users in this model. The way you've laid things out, if a user is destroyed, any topics, replies or comments they posted will also be removed. Instead your users should be deactivated.</p>
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    1. POhow to define a named_scope to roll up a has_many with nested models?
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    1. POhow to define a named_scope to roll up a has_many with nested models?
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    1. COThat's great! Thx for the excellent and fast reply. I had to edit your ':group_by' to ':group', but otherwise, it gives me just what I was looking for. I *knew* it had to be thru named_scope. And, yes, I agree with your pt about user deactivation vs destruction. Thx again.
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    2. COFollowup question: How would I get the list of Users who have posted to a particular Forum?
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    3. COI've updated the solution to correct the :group != :group_by mistake, and include a named scope that addresses your followup question. P.S. If you've found an answer helpful, you should vote it up. If it's solved your problem you should accept it. That way others who have a similar problem will find it easier to identify the correct solution.
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