如何修复此Rails AR查询以获取至少5分钟的记录？

Question

编写返回至少5分钟记录的Rails查询的最佳方法是什么？我使用的是Rails 3.0.1,Ruby 1.9.2和PostgreSQL.目前我有这个:

Note.order('date DESC').where('private_note = ? AND (?-created_at) > 300',false, Time.now.utc)

得到这些错误:

Note Load (0.7ms)  SELECT "notes".* FROM "notes" WHERE (private_note = 'f' AND ('2011-09-28 01:07:30.094475'-created_at) > 300) ORDER BY date DESC
PGError: ERROR:  operator does not exist: interval > integer
LINE 1: ...'f' AND ('2011-09-28 01:07:30.094475'-created_at) > 300) ORD...
                                                             ^
HINT:  No operator matches the given name and argument type(s). You might need to add explicit type casts.
: SELECT     "notes".* FROM       "notes"  WHERE     (private_note = 'f' AND ('2011-09-28 01:07:30.094475'-created_at) > 300) ORDER BY  date DESC
Completed   in 214ms

ActiveRecord::StatementInvalid (PGError: ERROR:  operator does not exist: interval > integer
LINE 1: ...'f' AND ('2011-09-28 01:07:30.094475'-created_at) > 300) ORD...
                                                             ^
HINT:  No operator matches the given name and argument type(s). You might need to add explicit type casts.
: SELECT     "notes".* FROM       "notes"  WHERE     (private_note = 'f' AND ('2011-09-28 01:07:30.094475'-created_at) > 300) ORDER BY  date DESC):
  app/controllers/notes_controller.rb:17:in `public_stream_get_notes'

一个示例created_at值是 2011-09-28 01:00:01 UTC

Answer 1

Note.where('created_at <= ?', 5.minutes.ago).where(:private_note => false).order('date DESC')