如何修复此 Rails AR 查询以获取至少 5 分钟前的记录？

Question

编写返回至少 5 分钟前的记录的 Rails 查询的最佳方法是什么？我正在使用 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)

它得到这些错误：

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'

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')

Answer 2

Note.where('created_at < ?', Time.now.utc - 5.minutes)

对于像 Time.now 这样的东西要记住的一件事是，如果您最终将其放入作用域中，请使用 lambda 而不是直接将其传递到作用域，否则 Time.now 将是常量。

scope :older_than_5_minutes, lambda { order(...).where('...', Time.now.utc - 5.minutes) }