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POHow to ORDER before GROUP with DBIx::Class
 

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  1. POHow to ORDER before GROUP with DBIx::Class
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    <p>I've got a simple temporal table that looks like this:</p> <pre><code>Table: item_approval item user status modified 2 fred approved 2010-12-01 00:00:00 3 fred approved 2010-12-02 00:00:00 4 fred disapproved 2010-12-03 00:00:00 7 jack unapproved 2010-12-05 00:00:00 4 fred approved 2010-12-06 00:00:00 4 jack unapproved 2010-12-07 00:00:00 4 fred disapproved 2010-12-04 00:00:00 </code></pre> <p>I'm using DBIx::Class. My "Item" result is defined with:</p> <pre><code>__PACKAGE__-&gt;has_many( "item_approvals", "Schema::Result::ItemApproval", { "foreign.item" =&gt; "self.id" }, { cascade_copy =&gt; 0, cascade_delete =&gt; 0 }, ); </code></pre> <p>Which means I can do:</p> <pre><code>my $item = $schema-&gt;resultset('Item')-&gt;find({id=&gt;4}); </code></pre> <p>Which is fine. Then, I can do:</p> <pre><code>my @approvals = $item-&gt;item_approvals; </code></pre> <p>to get a resultset like this:</p> <pre><code>item user status modified 4 fred disapproved 2010-12-03 00:00:00 4 fred approved 2010-12-06 00:00:00 4 jack unapproved 2010-12-07 00:00:00 4 fred disapproved 2010-12-04 00:00:00 </code></pre> <p>My question: How do I get the set of Fred and Jack's single most recent approval status? That is, I want to get this resultset:</p> <pre><code>item user status modified 4 fred approved 2010-12-06 00:00:00 4 jack unapproved 2010-12-07 00:00:00 </code></pre> <p>I tried things like this:</p> <pre><code>my @approvals = $item-&gt;search({}, { group_by =&gt; 'user', order_by =&gt; {-desc =&gt; 'modified'} }); </code></pre> <p>but the "ORDER BY" is executed <em>after</em> the "GROUP BY", so I get things like this instead:</p> <pre><code>item user status modified 4 fred disapproved 2010-12-03 00:00:00 4 jack unapproved 2010-12-07 00:00:00 </code></pre> <p>Help?</p>
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    1. USSir Robert
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    1. COI don't know perl or dbix, but the SQL way of doing this would be to make your `modified` field a `MAX(modified) as 'Modified'` which would return the highest date per user.
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    2. COI've played with this a bit, using things like: SELECT item, user, status, MAX(modified) as most_recent FROM item_approval WHERE id=4; but it doesn't return the highest date *per user*; it just returns the single row with the highest date.
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      1. USSir Robert
    3. COyou need to do both a `MAX(Modified)` AND `GROUP BY User`. The `MAX` without a `GROUP` gives you the max for the query. The `GROUP BY` gives you the max (or other aggregate functions like `SUM`, `AVG`, etc) for each group in the `GROUP BY`.
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