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    <p>A quick breakdown of what's going on, as it'll help you understand what to do for your replacement query.</p> <pre><code>options = { select: "SUM(1) AS num_demos, product_id ", group: "product_id", order: "num_demos ASC", } product_ids = Demo.where("state = 'waitlisted'").find(:all, options).collect{|d| d.product_id} </code></pre> <p>This line will generate </p> <pre><code>SELECT SUM(1) as num_demos, product_id FROM "demos" WHERE (state = 'waitlisted') GROUP BY product_id </code></pre> <p>And returns an array of <code>Demo</code> objects, sorted by the <code>count(*)</code> of rows in the group, where only the <code>product_id</code> attribute has been loaded, and is available to you.</p> <p>Next,</p> <pre><code>sort_product_ids = product_ids.collect{|product_id| "id = #{product_id}"} </code></pre> <p>results in a collection of product_ids mapped to the format <code>"id = x"</code>. IE: If the previous result returned 10 results, with product_ids ranging from 1..10, <code>sort_product_ids</code> is now equivalent to <code>["id = 1", "id = 2", "id = 3", "id = 4", "id = 5", "id = 6", "id = 7", "id = 8", "id = 9", "id = 10"]</code></p> <p>Finally,</p> <pre><code>Product.where(visible: true, id: product_ids).order(sort_product_ids.join(', ')) </code></pre> <p>Selects all <code>Products</code> where the column <code>visible</code> is <code>true</code>, and their <code>id</code> is in the array of <code>product_ids</code> (which, as we found out earlier, is actually an array of <code>Demo</code> objects, not integers - this might be causing the query to fail). Then, it asks SQL to sort that result list by the <code>sort_product_ids</code> (sent in as a string <code>"id = 1, id = 2, ... id = 10"</code> instead of an array <code>["id = 1", "id = 2", ... "id = 10"]</code>).</p> <p>More info available at: <a href="http://guides.rubyonrails.org/active_record_querying.html" rel="nofollow">http://guides.rubyonrails.org/active_record_querying.html</a> <a href="http://api.rubyonrails.org/classes/ActiveRecord/QueryMethods.html" rel="nofollow">http://api.rubyonrails.org/classes/ActiveRecord/QueryMethods.html</a></p>
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    1. COthank you for this useful analysis. In my tests in irb, the array sort_product_ids would have entries like "id = 1", "id = 2", etc. When you call join(', ') on that you should get a single string with all those entries thus: "id = 1, id = 2", etc. So does ActiveRecord actually create SQL that says ... ORDER BY ('id = 1, id = 2, ...') ?
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    2. COOops, meant to note that - updated!
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    3. COThanks a lot, @Morner. Would like to vote this answer up but I don't have enough reputation...
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