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    <p>Sadly people keep on using <code>has_and_belongs_to_many</code> even though it leads to all kinds of orphans like this. A <code>has_many ..., :through</code> relationship can be flagged <code>:dependent =&gt; :destroy</code> to clean up unused children automatically. It's common that you'll have unused join records and they are obnoxious to remove.</p> <p>What you might do is approach this from a SQL angle since <code>has_and_belongs_to_many</code> records are inaccessible if their parent records are no longer defined. They simply do not exist as far as ActiveRecord is concerned. Using a join model means you can always access this data since they are issued their own ids.</p> <p><code>has_and_belongs_to_many</code> relationships are based on a compound key which makes removing them a serious nuisance. Normally you'd do a <code>DELETE FROM table WHERE id IN (...) AND ...</code> and be confident that only the target records are removed. With a compound key you can't do this.</p> <p>You may find this works for an example Tag to Item relationship:</p> <pre><code>DELETE FROM item_tags, tags, items WHERE item_tags.tag_id=tags.id AND item_tags.item_id=items.id AND tags.id IS NULL AND items.id IS NULL </code></pre> <p>The <code>DELETE</code> statement can be really particular about how it operates and does not give the same latitude as a <code>SELECT</code> with joins that can be defined as left or right, inner or outer as required.</p> <p>If you had a primary ID key in your join table you could do it easily:</p> <pre><code>DELETE FROM item_tags WHERE id IN (SELECT id FROM item_tags LEFT JOIN tags ON item_tags.tag_id=tags.id LEFT JOIN items ON item_tags.item_id=items.id WHERE tags.id IS NULL AND items.id IS NULL) </code></pre> <p>In fact, it might be advantageous to add a primary key to your relationship table even if ActiveRecord ignores it.</p> <p><em>Edit:</em></p> <p>As for your module issue, if you're stuck with that approach:</p> <pre><code>module CleanupMethods def cleanup # ... end end class Tag # Import the module methods as class methods extend CleanupMethods end </code></pre> <p>If you use a counter cache column you can do this a lot more easily, but you will also have to ensure your counter caches are accurate.</p>
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Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

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