在给定的时间间隔后，我可以定期重新计算属性吗？ [英] Can I periodically recalculate an attribute after a given time interval?

问题描述

我有一个模型User，有一个float属性Value。我想让每个用户的价值在用户创建后每24小时贬值1％（即乘以0.99）。例如，如果用户在1月1日的02:34，1月2日的02:34创建了值为5的用户，则其值应重新计算为4.95。然后在1月3日02:34，应该重新计算为4.9005，依此类推。

可以这样做吗？

我使用的是Rails 4.0.10应用程式，

解决方案

使用 delayed_job gem你可以这样做：

 ＃in user.rb 
 after_create：decrease_value_periodically 
 
 private 
 def decrease_value_periodically 
 self.value = value * 0.99 
 self.save！ 
 
 decrease_value_periodically如果value> 0 
 end 
 handle_asynchronously：decrease_value_periodically，
：run_at => Proc.new {24.hours.from_now} 
  

此示例将在创建用户后24小时运行

---

另一个选项可能是每天的Cron任务重新计算所有用户的值同时（例如午夜）。你可以设置一个Cron任务运行一个Rails方法，像这样：

 ＃命令为Cron 
 rails .recalculate_all_values
 
＃在user.rb中
 def self.recalculate_all_values 
 User.all.each {| user | user.decrease_value} 
 end 
 
 private 
 def decrease_value 
如果值> 0 
 self.value = value * 0.99 
 self.save！ 
 end 
 end 
  

IMO这取决于你的优先级：精确运行24小时后，选择delayed_jobs。虽然Cron解决方案更容易维护，但是您可能最终将值递减为早或晚（假设用户在晚上11点创建，一小时后Cron任务开始第一次降低值）。

I have a model "User", with a float attribute "Value". I want each User's Value to depreciate 1%(i.e., be multiplied by 0.99) every 24 hours after the User's creation. For example, if a User is created with a Value of 5 at 02:34 on January 1st, then at 02:34 on January 2nd, its value should be recalculated to be 4.95. Then at 02:34 on January 3rd, it should be recalculated to be 4.9005, and so on.

Can this be done?

I'm using a Rails 4.0.10 app, if that matters.

解决方案

With the delayed_job gem you could do something like this:

# in user.rb
after_create :decrease_value_periodically

private
def decrease_value_periodically
  self.value = value * 0.99
  self.save!

  decrease_value_periodically if value > 0
end
handle_asynchronously :decrease_value_periodically, 
                      :run_at => Proc.new { 24.hours.from_now }

This example would run 24 hours after creation of an user and would reschedule itself over and over again.

---

Another option might be a daily Cron task that recalculates all user's values at the same time (midnight for example). You could setup a Cron task that runs a Rails method like this:

# command for Cron
rails runner "User.recalculate_all_values"

# in user.rb
def self.recalculate_all_values
  User.all.each { |user| user.decrease_value }
end

private
def decrease_value
  if value > 0
    self.value = value * 0.99
    self.save!
  end
end

IMO it depends on your priorities: If you want a precise run after 24 hours, choose delayed_jobs. Whereas the Cron solution is easier to maintain, but you might end up with decreasing values to early or to late (Imagine a user is created at 11pm and one hour later the Cron task starts to decrase the value for the first time).

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