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copied!<p>Okay - after struggling on and off with this, I crack it within 10mins of posting to stackoverflow! Typical.</p> <p>To save others from banging their heads against walls, here's what I had wrong:</p> <p>Note should have been:</p> <pre><code>class Note < ActiveRecord::Base has_one :card, :through => :timeline_item #not timeline_items has_one :timeline_item, :as => :item end </code></pre> <p>And that was it! I was trying to use the creation methods used in <a href="https://gist.github.com/1242485" rel="nofollow">this article</a>, but actually that's not required.</p> <p>Here's the console output, showing that the sql statements are all using the timeline_items table:</p> <pre><code>1.9.2-p290 :009 > c = Card.find(547) Card Load (0.3ms) SELECT `cards`.* FROM `cards` WHERE `cards`.`id` = 547 LIMIT 1 => #<Card id: 547, name: "Duplicates appearing"> 1.9.2-p290 :010 > c.notes.count (0.3ms) SELECT COUNT(*) FROM `notes` INNER JOIN `timeline_items` ON `notes`.`id` = `timeline_items`.`item_id` WHERE `timeline_items`.`card_id` = 547 AND `timeline_items`.`item_type` = 'Note' => 4 1.9.2-p290 :011 > c.notes.last.card Note Load (2.7ms) SELECT `notes`.* FROM `notes` INNER JOIN `timeline_items` ON `notes`.`id` = `timeline_items`.`item_id` WHERE `timeline_items`.`card_id` = 547 AND `timeline_items`.`item_type` = 'Note' ORDER BY updated_at ASC LIMIT 1 Card Load (3.2ms) SELECT `cards`.* FROM `cards` INNER JOIN `timeline_items` ON `cards`.`id` = `timeline_items`.`card_id` WHERE `timeline_items`.`item_id` = 620 AND `timeline_items`.`item_type` = 'Note' LIMIT 1 => #<Card id: 547, name: "Duplicates appearing"> 1.9.2-p290 :013 > c.notes << Note.new(:content => 'Holee Sheeet Dawg', :user_id => 1) (0.2ms) BEGIN SQL (0.6ms) INSERT INTO `notes` (`content`, `created_at`, `updated_at`, `user_id`) VALUES ('Holee Sheeet Dawg', '2012-09-07 11:38:55', '2012-09-07 11:38:55', 1) (0.1ms) COMMIT (0.1ms) BEGIN SQL (0.3ms) INSERT INTO `timeline_items` (`card_id`, `created_at`, `item_id`, `item_type`, `updated_at`) VALUES (547, '2012-09-07 11:38:55', 625, 'Note', '2012-09-07 11:38:55') (0.5ms) COMMIT Note Load (1.8ms) SELECT `notes`.* FROM `notes` INNER JOIN `timeline_items` ON `notes`.`id` = `timeline_items`.`item_id` WHERE `timeline_items`.`card_id` = 547 AND `timeline_items`.`item_type` = 'Note' ORDER BY updated_at DESC => [#<Note id: 625, content: "Holee Sheeet Dawg", user_id: 1, created_at: "2012-09-07 11:38:55", updated_at: "2012-09-07 11:38:55">, .....] 1.9.2-p290 :014 > c.notes.count (0.7ms) SELECT COUNT(*) FROM `notes` INNER JOIN `timeline_items` ON `notes`.`id` = `timeline_items`.`item_id` WHERE `timeline_items`.`card_id` = 547 AND `timeline_items`.`item_type` = 'Note' => 5 </code></pre> <p><strong>EDIT:</strong></p> <p>I just noticed that my requirement of having <em>card.timeline</em> wasn't met yet. Because the join is coming from multiple tables, I wasn't able to get AR to handle the join for me (ideally *card.timeline_items.join(:notes, :attachments)* would have done the trick).</p> <p>To solve this, I added the following method to my card class:</p> <pre><code> def timeline (self.notes + self.attachments).sort { |a,b| a.updated_at <=> b.updated_at } end </code></pre>

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