blocks|key|982172|text|如果你使用的是Rails或者不介意包含ActiveSupport，你可以这样使用Numeric#days+DSL：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|982173|ruby-1.9.2-p136+:002+>+Date.today
+=>+Wed,+02+Mar+2011+
ruby-1.9.2-p136+:003+>+Date.today+-+90.days
+=>+Thu,+02+Dec+2010+|code-block|syntax|javascript|982174|由于您使用的是日期而不是时间，因此您还应该从Date实例开始，或者使用#to_date转换您的DateTime实例。当从date实例中添加/减去数字时，这些数字隐式地是天数。|982175|ruby-1.9.2-p136+:016+>+DateTime.now.to_date
+=>+#<Date:+2011-03-02+(4911245/2,0,2299161)>+
ruby-1.9.2-p136+:017+>+DateTime.now.to_date+-+90
+=>+#<Date:+2010-12-02+(4911065/2,0,2299161)>+|982176|entityMap|0|LINK|mutability|MUTABLE|url|http://api.rubyonrails.org/classes/Numeric.html#method-i-days^0|14|C|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@$A|V|B|W|1|X]]|C|$]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|Z|8|@]|9|@]|C|$]]|$1|K|3|L|5|F|7|10|8|@]|9|@]|C|$G|H]]|$1|M|3|-4|5|6|7|11|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]]]

If you're using Rails or don't mind including ActiveSupport, you can use the <a href="http://api.rubyonrails.org/classes/Numeric.html#method-i-days" rel="noreferrer">Numeric#days</a> DSL like this:

<pre><code>ruby-1.9.2-p136 :002 &gt; Date.today
 =&gt; Wed, 02 Mar 2011 
ruby-1.9.2-p136 :003 &gt; Date.today - 90.days
 =&gt; Thu, 02 Dec 2010 
</code></pre>

Since you are working with dates instead of times, you should also either start with Date instances, or convert your DateTime intances with #to_date. When adding/subtracting numbers from date instances, the numbers are implicitly days.

<pre><code>ruby-1.9.2-p136 :016 &gt; DateTime.now.to_date
 =&gt; #&lt;Date: 2011-03-02 (4911245/2,0,2299161)&gt; 
ruby-1.9.2-p136 :017 &gt; DateTime.now.to_date - 90
 =&gt; #&lt;Date: 2010-12-02 (4911065/2,0,2299161)&gt; 
</code></pre>

blocks|key|767152|text|对于使用Rails的用户，请查看以下内容：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|767153|DateTime.now+-+10.days
=>+Sat,+04+May+2013+12:12:07+%2B0300

20.days.ago+-+10.days
=>+Sun,+14+Apr+2013+09:12:13+UTC+%2B00:00|code-block|syntax|javascript|767154|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

For those using Rails, check out the following:

<pre><code>DateTime.now - 10.days
=&gt; Sat, 04 May 2013 12:12:07 +0300

20.days.ago - 10.days
=&gt; Sun, 14 Apr 2013 09:12:13 UTC +00:00
</code></pre>

blocks|key|767214|text|这是一个非常老的帖子，但是如果你想继续使用Time对象，而不是切换到Date对象，你可能会考虑使用Ruby+Facets。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|767215|Ruby+Facets是核心Ruby类的标准扩展库。|767216|http://rubyworks.github.io/facets/|767217|通过需要Facets，您可以对Time对象执行以下操作。|767218|Time.now.less(90,+:days)|767219|entityMap|0|LINK|mutability|MUTABLE|url^0|L|4|Y|4|1D|B|0|0|0|Y|0|0|0|0|O|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|11|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|12|8|@]|D|@$9|13|A|14|1|15]]|E|$]]|$1|J|3|K|5|6|7|16|8|@]|D|@]|E|$]]|$1|L|3|M|5|6|7|17|8|@$9|18|A|19|B|C]]|D|@]|E|$]]|$1|N|3|-4|5|6|7|1A|8|@]|D|@]|E|$]]]|O|$P|$5|Q|R|S|E|$T|I]]]]

This is a super old post, but if you wanted to keep with a <code>Time</code> object, like was originally asked, rather than switching to a <code>Date</code> object you might want to consider using <code>Ruby Facets</code>.

Ruby Facets is a standardized library of extensions for core Ruby classes.

<a href="http://rubyworks.github.io/facets/" rel="noreferrer">http://rubyworks.github.io/facets/</a>

By requiring Facets you can then do the following with Time objects.

<code>Time.now.less(90, :days)</code>

blocks|key|767299|text|Ruby在Date+and+DateTime+classes中支持日期算法，这是Ruby标准库的一部分。这两个类都公开了#%2B和#-方法，它们可以从日期或时间中添加和减去日期。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|767300|$+irb
+>+require+'date'
+=>+true+
+>+(DateTime.new(2015,4,1)+-+90).to_s++#+Apr+1,+2015+-+90+days
+=>+"2015-01-01T00:00:00%2B00:00"
+>+(DateTime.new(2015,4,1)+-+1).to_s+++#+Apr+1,+2015+-+1+day
+=>+"2015-03-31T00:00:00%2B00:00"+|code-block|syntax|javascript|767301|使用#<<和#>>方法按月操作，而不是按天操作。以月为单位的算术与以日为单位的算术略有不同。使用Date而不是DateTime会使效果更加明显。|767302|+>+(Date.new(2015,+5,+31)+<<+3).to_s++#+May+31+-+3+months;+92+days+diff
+=>+"2015-02-28"+|767303|按照您的joda-time示例，您可以用Ruby编写类似下面这样的代码。|767304|now+=++DateTime.now
ninety_days_ago+=+now+-+90|767305|或者仅仅是|767306|ninety_days_ago+=+DateTime.now+-+90|767307|entityMap|0|LINK|mutability|MUTABLE|url|http://ruby-doc.org/stdlib-2.2.1/libdoc/date/rdoc/Date.html|1|http://ruby-doc.org/stdlib-2.2.1/libdoc/date/rdoc/Date.html#method-i-2B|2|http://ruby-doc.org/stdlib-2.2.1/libdoc/date/rdoc/Date.html#method-i-2D|3|http://ruby-doc.org/stdlib-2.2.1/libdoc/date/rdoc/Date.html#method-i-3C-3C|4|http://ruby-doc.org/stdlib-2.2.1/libdoc/date/rdoc/Date.html#method-i-3E-3E^0|5|P|0|1O|2|1|1R|2|2|0|0|2|3|3|6|3|4|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1A|8|@]|9|@$A|1B|B|1C|1|1D]|$A|1E|B|1F|1|1G]|$A|1H|B|1I|1|1J]]|C|$]]|$1|D|3|E|5|F|7|1K|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|1L|8|@]|9|@$A|1M|B|1N|1|1O]|$A|1P|B|1Q|1|1R]]|C|$]]|$1|K|3|L|5|F|7|1S|8|@]|9|@]|C|$G|H]]|$1|M|3|N|5|6|7|1T|8|@]|9|@]|C|$]]|$1|O|3|P|5|F|7|1U|8|@]|9|@]|C|$G|H]]|$1|Q|3|R|5|6|7|1V|8|@]|9|@]|C|$]]|$1|S|3|T|5|F|7|1W|8|@]|9|@]|C|$G|H]]|$1|U|3|-4|5|6|7|1X|8|@]|9|@]|C|$]]]|V|$W|$5|X|Y|Z|C|$10|11]]|12|$5|X|Y|Z|C|$10|13]]|14|$5|X|Y|Z|C|$10|15]]|16|$5|X|Y|Z|C|$10|17]]|18|$5|X|Y|Z|C|$10|19]]]]

Ruby supports date arithmetic in the <a href="http://ruby-doc.org/stdlib-2.2.1/libdoc/date/rdoc/Date.html" rel="noreferrer">Date and DateTime classes</a>, which are part of Ruby's standard library. Both those classes expose <a href="http://ruby-doc.org/stdlib-2.2.1/libdoc/date/rdoc/Date.html#method-i-2B" rel="noreferrer">#+</a> and <a href="http://ruby-doc.org/stdlib-2.2.1/libdoc/date/rdoc/Date.html#method-i-2D" rel="noreferrer">#-</a> methods, which add and subtract days from a date or a time.

<pre><code>$ irb
 &gt; require 'date'
 =&gt; true 
 &gt; (DateTime.new(2015,4,1) - 90).to_s # Apr 1, 2015 - 90 days
 =&gt; "2015-01-01T00:00:00+00:00"
 &gt; (DateTime.new(2015,4,1) - 1).to_s # Apr 1, 2015 - 1 day
 =&gt; "2015-03-31T00:00:00+00:00" 
</code></pre>

Use the <a href="http://ruby-doc.org/stdlib-2.2.1/libdoc/date/rdoc/Date.html#method-i-3C-3C" rel="noreferrer">#&lt;&lt;</a> and <a href="http://ruby-doc.org/stdlib-2.2.1/libdoc/date/rdoc/Date.html#method-i-3E-3E" rel="noreferrer">#>></a> methods to operate on months instead of days. Arithmetic on months is a little different than arithmetic on days. Using Date instead of DateTime makes the effect more obvious.

<pre><code> &gt; (Date.new(2015, 5, 31) &lt;&lt; 3).to_s # May 31 - 3 months; 92 days diff
 =&gt; "2015-02-28" 
</code></pre>

Following your joda-time example, you might write something like this in Ruby.

<pre><code>now = DateTime.now
ninety_days_ago = now - 90
</code></pre>

or maybe just

<pre><code>ninety_days_ago = DateTime.now - 90
</code></pre>

blocks|key|767369|text|使用秒数：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|767370|Time.now+-+90*24*60*60|code-block|syntax|javascript|767371|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

use the number of seconds:

<pre><code>Time.now - 90*24*60*60
</code></pre>

blocks|key|982452|text|使用Rails主动支持的简单解决方案：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|982453|days90_ago+=+90.days.ago.to_date.to_s

OUTPUT:
puts+90_days_ago
=>+"2019-10-09"+#+considering+cur_date:+2020-01-07|code-block|syntax|javascript|982454|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Simple solution using Rails Active Support:
<pre><code>days90_ago = 90.days.ago.to_date.to_s

OUTPUT:
puts 90_days_ago
=&gt; &quot;2019-10-09&quot; # considering cur_date: 2020-01-07
</code></pre>

I've been a bit spoiled by the joda-time API of:

<pre><code>DateTime now = new DateTime();
DateTime ninetyDaysAgo = now.minusDays(90);
</code></pre>

I'm trying to do a similar thing in Ruby, but I'm 

<pre><code>now = Time.now
ninetyDaysAgo = now - (90*24)
</code></pre>

However, the math is off here (I'm really working with dates at midnight).

Is there friendly API for date subtraction?

Ruby Date Subtraction (e.g. 90 days Ago)

我有点被joda-time API宠坏了：DateTime now = new DateTime();DateTime ninetyDaysAgo = now.minusDays(90);我也在尝试用Ruby做类似的事情，但是我now = Time.nowninetyDaysAgo = now - (90*24)然而，...

问Ruby日期减法(例如90天前)
EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问Ruby日期减法(例如90天前)EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问Ruby日期减法(例如90天前)
EN