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copied!<pre><code>do_something_with( item.collection_item_id ) </code></pre> <p>This fails because item does not have a collection_item_id member.</p> <pre><code>do_something_with( item.collection_item.collection_item_id ) </code></pre> <p>This fails because item does not have a collection_item member.</p> <p>Remember that the relation between item and collection_items is a has_many. So item has collection_items, not just a single item. Also, each collection has a list of collection items. What you want to do is probably this:</p> <pre><code>colls = Collection.find :all colls.each do |coll| coll.collection_items.each do |collection_item| do_something_with( collection_item.id ) end end </code></pre> <p>A couple of other pieces of advice:</p> <ul> <li>Have you read the <a href="http://guides.rubyonrails.org/association_basics.html#thehas-manythroughassociation" rel="nofollow noreferrer">documentation for has_many :through</a> in the Rails Guides? It is pretty good.</li> <li>You shouldn't need the :source parameters in the has_many declarations, since you have named your models and associations in a sensible way.</li> </ul> <blockquote> <p>I found from online documentation that using has_and_belongs_to_many will attach the join table attributes to the retreived items, but apparently it is deprecated. I haven't tried it yet.</p> </blockquote> <p>I recommend you stick with has_many :through, because has_and_belongs_to_many is more confusing and doesn't offer any real benefits.</p>

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