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    <p>It is possible but I've only managed to do it using two database trips. </p> <p>The main issue stems from not being able to set limits on a node's children, which leads to either a node's children being truncated or children being orphaned on subsequent pages.</p> <p>An example:</p> <pre><code>id: 105, Ancestry: Null id: 117, Ancestry: 105 id: 118, Ancestry: 105/117 id: 119, Ancestry: 105/117/118 </code></pre> <p>A LIMIT 0,3 (for the sake of the example above) would return the first three records, which will render all but id:119. The subsequent LIMIT 3,3 will return id: 119 which will not render correctly as its parents are not present.</p> <p>One solution I've employed is using two queries:</p> <ol> <li>The first returns root nodes only. These can be sorted and it is this query that is paginated.</li> <li>A second query is issued, based on the first, which returns all children of the paginated parents. You should be able to sort children per level.</li> </ol> <p>In my case, I have a Post model (which has_ancestry) . Each post can have any level of replies. Also a post object has a replies count which is a cache counter for its immediate children.</p> <p>In the controller:</p> <pre><code>roots = @topic.posts.roots_only.paginate :page =&gt; params[:page] @posts = Post.fetch_children_for_roots(@topic, roots) </code></pre> <p>In the Post model:</p> <pre><code>named_scope :roots_only, :conditions =&gt; 'posts.ancestry is null' def self.fetch_children_for_roots(postable, roots) unless roots.blank? condition = roots.select{|r|r.replies_count &gt; 0}.collect{|r| "(ancestry like '#{r.id}%')"}.join(' or ') unless condition.blank? children = postable.posts.scoped(:from =&gt; 'posts FORCE INDEX (index_posts_on_ancestry)', :conditions =&gt; condition).all roots.concat children end end roots end </code></pre> <p>Some notes:</p> <ul> <li>MySQL will stop using the ancestry column index if multiple LIKE statements are used. The FORCE INDEX forces mySQL to use the index and prevents a full table scan</li> <li>LIKE statements are only built for nodes with direct children, so that replies_count column came in handy</li> <li>What the class method does is appends children to root, which is a WillPaginate::Collection </li> </ul> <p>Finally, these can be managed in your view:</p> <pre><code> =will_paginate @posts -Post.arrange_nodes(@posts).each do |post, replies| =do stuff here </code></pre> <p>The key method here is <strong>arrange_nodes</strong> which is mixed in from the ancestry plugin and into your model. This basically takes a sorted Array of nodes and returns a sorted and hierarchical Hash.</p> <p>I appreciate that this method does not directly address your question but I hope that the same method, with tweaks, can be applied for your case.</p> <p>There is probably a more elegant way of doing this but overall I'm happy with the solution (until a better one comes along).</p>
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