Activerecord memo (2)

Find的參數
1.select
<br />#select 可以只選出我們想要的<br />f = Forum.find(:all, :joins => :user, :select => "forums.*, users.name")<br />#如果參數是設成 :select => "*" 那麼users全部的attributes 也會被select 進去<br />>> f[0].attributes<br />=> {"name"=>"iflakela", "last_comment_time"=>Sat Aug 23 19:34:17 +0800 2008, "public"=>nil, "subject"=>"111111111", "id"=>6, "group_id"=>1, "content"=>"11111111", "user_id"=>1, "comments_count"=>2, "created_at"=>Sat Aug 23 19:19:02 +0800 2008}<br /><br />>> f[0].attribute_names<br />=> ["comments_count", "content", "created_at", "group_id", "id", "last_comment_time", "name", "public", "subject", "user_id"]<br /><br />#判斷有沒有這個attribute<br />>> f[0].attribute_present?("lala")<br />=> fales<br />
2.group
<br /> Forum.find(:all, :group => 'DATE(created_at)', :select => "subject, DATE(created_at)")<br /> SELECT subject, DATE(created_at) at FROM `forums` GROUP BY DATE(created_at);<br />+--------------------------+-----------------+<br />| subject | DATE(created_at) |<br />+--------------------------+-----------------+<br />| 111111111 | 2008-08-23 |<br />| cc | 2008-08-27 |<br />| aaaaaaaaaaaaa | 2008-08-29 |<br />| a | 2008-09-03 |<br />| dddddddd | 2008-12-07 |<br />| 333333333333 | 2008-12-13 |<br />| 1111111 | 2008-12-14 |<br />| lalalal | 2008-12-28 |<br />
統計的method
有average, maximum, minimum, sum, count
1. count, group
<br />#每天forum 的數目<br />>> Forum.count(:all, :group => 'DATE(created_at)')<br />=> [["2008-08-23", 6], ["2008-08-27", 1], ["2008-08-29", 1], ["2008-09-03", 1], ["2008-12-07", 3], ["2008-12-13", 2], ["2008-12-14", 3], ["2008-12-28", 3], ["2009-01-03", 2], ["2009-01-08", 1]]<br />
2. maximum
<br /> Status.maximum :score, :group => "user_id", :limit => 3, :order => "max(score) desc"<br />=> [[2, 3], [4, 3], [6, 2]]<br />SELECT max(`statuses`.score) AS max_score, user_id FROM `statuses` GROUP BY user_id ORDER BY max(score) desc LIMIT 3;<br />+-----------+---------+<br />| max_score | user_id |<br />+-----------+---------+<br />| 3 | 2 | <br />| 3 | 4 | <br />| 2 | 6 | <br />+-----------+---------+<br /><br />
memo: find_by_sql, count_by_sql
<br />u = User.find_by_sql("select * from forums, users where forums.user_id=users.id")<br /><br />count = LineItem.count_by_sql("select count(*) " +<br /> " from line_items, orders " +<br /> " where line_items.order_id = orders.id " +<br /> " and orders.name = 'Dave Thomas' " )<br />
find_or_initialize_by, find_or_create_by