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PORails custom validation checking for duplicates
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copied!<p>A table has following fields: badge_id, output_id, timely, removed, updated_at. For each badge_id, there can't have two valid records with the same output_id. But it doesn't mean that (badge_id, output_id) is a unique combination. Removed column indicates the current row has been removed or not. Basically delete or update operation triggers inserting a new row in the table with the latest change. So for example, we have a record like this:</p> <pre><code>badge_id| output_id| removed| timely | updated_at 1 | 1 | N | Y | 2013-11-26 </code></pre> <p>To remove that record, we actually insert another row and now it reads like</p> <pre><code>badge_id| output_id| removed| timely | updated_at 1 | 1 | N | Y | 2013-11-26 1 | 1 | Y | Y | 2013-11-27 </code></pre> <p>Because the latest record of (badge_id: 1, output_id: 1) has removed column set, it means that combination has been deleted. But I can't have two rows of same (badge_id: 1, output_id: 1), both have removed as "N" like:</p> <pre><code>badge_id| output_id| removed| timely | updated_at 1 | 1 | N | N | 2013-11-26 1 | 1 | N | Y | 2013-11-27 </code></pre> <p>So every time to add a new output_id for a certain badge_id, I have to check for duplication. But usual validates uniqueness of (badge_id, output_id) from ActiveModel doesn't work here. How do I write a clean custom validation for this? Thanks.</p> <p><strong>UPDATE:</strong></p> <p>I think I might have missed some key points. A record can be added and then deleted and then added repeatedly. So a combination of (badge_id, output_id, removed) isn't unique either. When add a new record, we need to check for (badge_id, output_id), whether <strong>latest</strong> record has removed set as 'Y' or not. </p> <p>So for possible answer like </p> <pre><code>validate_uniqueness_of :badge_id, scope: [:output_id], conditions: -> { where(removed: "N") } </code></pre> <p>At the condition where clause, it should have order by updated_at desc and the first one has removed: 'N'. How do I fit that kind of condition into this one line code? Or there's a better way of doing this?</p>

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