我需要为缓存到期目的总结一组日期时间，例如
# posts_controller.rb
@posts = Post.all
# index.html.erb
<% cache [:posts, :index, @posts.sum(&:updated_at)] do %>
# ...
我认为这等于：
@posts.map(&:updated_at).reduce(:+)
问题是代码在本地正常工作（缓存和控制台测试）但在部署到heroku时在生产中返回以下错误：
TypeError: not an integer
from /app/vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/core_ext/date_time/calculations.rb:67:in `convert'
from /app/vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/core_ext/date_time/calculations.rb:67:in `Rational'
from /app/vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/core_ext/date_time/calculations.rb:67:in `since'
from /app/vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/core_ext/time/calculations.rb:116:in `rescue in since'
from /app/vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/core_ext/time/calculations.rb:114:in `since'
from /app/vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/time_with_zone.rb:223:in `rescue in +'
from /app/vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/time_with_zone.rb:223:in `+'
from (irb):25:in `each'
from (irb):25:in `reduce'
from (irb):25
from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.13/lib/rails/commands/console.rb:47:in `start'
from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.13/lib/rails/commands/console.rb:8:in `start'
from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.13/lib/rails/commands.rb:41:in `<top (required)>'
from script/rails:6:in `require'
from script/rails:6:in `<main>'
Ruby版本是相同的（1.9.3）。 Rails版本是相同的（3.2.13）。
提前致谢。
修改
@posts.map(&:updated_at)
包含
[Thu, 11 Jul 2013 18:35:53 UTC +00:00, Thu, 11 Jul 2013 18:35:58 UTC +00:00,
Thu,11 Jul 2013 18:36:02 UTC +00:00, Thu, 11 Jul 2013 18:36:05 UTC +00:00,
Thu, 11 Jul 2013 18:36:09 UTC +00:00, Thu, 11 Jul 2013 18:36:14 UTC +00:00,
Thu, 11 Jul 2013 18:36:18 UTC +00:00]
答案 0 :(得分：0)
您可以尝试将缓存键设置为最近更新的帖子吗？
<% cache [:posts, :index, @posts.order(:updated_at).last] do %>