Kohana ORM（自定义查询）与MySQL ORDER BY和GROUP BY

Question

I have a table with messages. I want to group these messages into conversations, checking if there is unread messages and previewing the latest message.

My current ORM looks like this:

$text = new Model_Text;
$text->select(DB::expr('min(`text`.`read`) AS `read_all`'))
->where('time', '>', $time_offset);
->order_by('read', 'DESC')->order_by('time', 'ASC')
->group_by('contact')->with('user')->find_all();

But as you know MySQL groups before it orders, meaning I don't get the latest message, while the min('text'.'read') trick makes sure I always know if the conversation has unread messages.

To get the latest message in each conversation, I would do a MySQL query like this:

SELECT min(q1.`read`) as read_all, q2.* FROM texts q1 
INNER JOIN (
    SELECT * FROM texts ORDER BY time DESC
) q2 ON(q1.contact = q2.contact) 
GROUP BY q1.contact 
ORDER BY q2.`time` DESC, q2.`read` ASC

But I am completely lost as for how to optimally implement this query with ORM.

My best guess would be to execute the above query directly with Kohana's DB class and load an ORM object for each row returned. But, this will cause one database hit for each and every conversation loaded into ORM, for data that I already retrieved - stupid!

Let me know your thoughts!

Thanks.

Answer 1

There is not a good way to do this with the ORM class, even if you could select the data properly, you wouldn't be able to read it back, as your Model_Text won't have the read_all property.

I think the best way to do this is with two queries, The first would be to get the conversations that you are interested in, select contact, min(read) as read_all ... where time > $time_offset and group by contact . Once you have the contact and read_all, you can make another query the get just the latest text for each conversation and load that into your Model_Text as suggested by Carl: DB::query(DATABASE::SELECT, $sql)->as_object('Model_Text')->execute()