Ruby-on-rails 你如何从日期时间中减去？
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How do you subtract from a datetime?
提问by Trip
I'd like to write a simple function to say in hours:
我想写一个简单的函数，以小时为单位：
How much time has passed since this has been created?
自创建以来已经过去了多少时间？
My attempts:
我的尝试：
-time = DateTime.now.hour - (self.created_at.hour)
Does anyone know how to do this in Ruby on Rails?
有谁知道如何在 Ruby on Rails 中做到这一点？
回答by mckeed
Rails usually uses Time, not DateTime. Why don't you do Time.now - self.created_at? Then you can convert from seconds to hours by dividing by 3600.
Rails 通常使用Time，而不是DateTime. 你为什么不做Time.now - self.created_at？然后您可以通过除以 3600 将秒转换为小时。
回答by Trip
Got it!. First you have to make sure your data is in the same data it will be subtracted from whether its a Time or a DateTime. I chose time. Then you divide it by Ruby's built in time methods. This translates into how many days, but it can also be, 1.hour. etc.
知道了！。首先，您必须确保您的数据与从时间或日期时间中减去的数据相同。我选择了时间。然后你将它除以 Ruby 的内置时间方法。这转化为多少天，但也可以是 1.hour。等等。
(Time.now - self.created_at.to_time)/1.day
回答by sosborn
You are looking for the time_ago_in_words(from_time, include_seconds = false) function. Here are some examples from the docs:
您正在寻找 time_ago_in_words(from_time, include_seconds = false) 函数。以下是文档中的一些示例：
time_ago_in_words(3.minutes.from_now) # => 3 minutes
time_ago_in_words(Time.now - 15.hours) # => 15 hours
time_ago_in_words(Time.now) # => less than a minute
from_time = Time.now - 3.days - 14.minutes - 25.seconds # => 3 days
