post.rb

 named_scope :unfiltered,   { }
   named_scope :not_hidden,   :conditions => { :hidden     => false }
   named_scope :not_private,  :conditions => { :private    => false }
   named_scope :not_not_private,  :conditions => { :private => true }
   named_scope :restricted,   :conditions => { :restricted => true  }
   named_scope :unrestricted, :conditions => { :restricted => false, :initiation => false }

   named_scope :interesting,  lambda { |user|
     { :conditions => { :user_id => user.friends.map(&:id) } }
   }

   named_scope :my, lambda { |user|
     {
       :select     => 'DISTINCT posts.*',
       :joins      => [:post_views, :comments],
       :conditions => [ 'comments.user_id = :uid OR posts.user_id = :uid', {:uid => user.id} ]
     }
   }

  named_scope :has_unread_comments, lambda { |user|
     {
       :joins => %Q(LEFT JOIN post_views pw ON pw.post_id = posts.id AND pw.user_id = #{user.id}
                    LEFT JOIN comments unread_comments ON unread_comments.post_id = posts.id),
       :conditions => 'unread_comments.created_at > pw.last_viewed',
       :group      => 'unread_comments.post_id',
       :having     => 'count(unread_comments.post_id) > 0'
     }
   }

   named_scope :unread, lambda { |user|
     {
       :select => "distinct posts.*",
       :joins  => %Q(LEFT OUTER JOIN post_views pv_unread ON pv_unread.post_id = posts.id AND pv_unread.user_id = #{user.id}
                     LEFT OUTER JOIN comments c_unread ON c_unread.post_id = posts.id),
       :conditions => '(c_unread.created_at > pv_unread.last_viewed OR (c_unread.id IS NULL AND pv_unread.id IS NULL)) OR pv_unread.id IS NULL'
     }
   }

   named_scope :descend_by_created_at, { :order => 'posts.created_at DESC' }
   named_scope :accessible_by, lambda { |user|
     {
       :select => "DISTINCT posts.*",
       :joins => "LEFT OUTER JOIN post_accesses ON post_accesses.post_id = posts.id",
       :conditions => ['post_accesses.user_id = ? OR posts.user_id = ?', user.id, user.id ]
     }
   }