ruby-on-rails - 您如何找到一天在一个月中的星期几？

Question

我似乎无法理解这个可能很简单的问题..

假设我有日期..

Fri, 14 Sep 2012 18:37:50 +0200

我如何找出这个月的这个日期是星期几？是第一个，第二个..？第三个？

谢谢!

Answer 1

为什么要使用图书馆？ Ruby 默认有它:

Week number:
The week 1 of YYYY starts with a Sunday or Monday (according to %U
  or %W).  The days in the year before the first week are in week 0.
    %U - Week number of the year.  The week starts with Sunday.  (00..53)
    %W - Week number of the year.  The week starts with Monday.  (00..53)

> Time.zone.parse("2012-01-01").strftime("%U")
=> "01" 

因此，鉴于我们可以找到给定日期在一年中的第几周，我们可以做一些数学运算来计算出它发生在一个月中的第几周。

> week_of_year_for_first_of_month = Time.zone.parse("2012-07-01").strftime("%U").to_i
> week_of_target_date = Time.zone.parse("2012-07-14").strftime("%U").to_i
> week_occurs_in = week_of_target_date - week_of_year_for_first_of_month + 1
> week_occurs_in # => 2

或者一个方法:

def week_of_month_for_date(date)
  my_date = Time.zone.parse(date)
  week_of_target_date = my_date.strftime("%U").to_i
  week_of_beginning_of_month = my_date.beginning_of_month.strftime("%U").to_i
  week_of_target_date - week_of_beginning_of_month + 1
end

> week_of_month_for_date("2012-07-14") # => 2 
> week_of_month_for_date("2012-07-15") # => 3