Question

如果我想知道上个月的哪个日期是第一个星期一，即月份的第一个beginning_of_week，我可以先了解最后的情况：

Date.current - 1.month

并且也是那个月的开头：

(Date.current - (1.month)).beginning_of_month

但是，我怎样才能有效地了解当月第一周开始的日期？

Answer 1

您可以执行以下操作：

date = (Date.current - (1.month)).beginning_of_month
date += 1.days until date.wday == 1 # wday 1 is monday
# why you english people consider Sunday as the first day of the week ?! ahah

我的IRB控制台中的输出：

1.9.3p489> date = (Date.current - (1.month)).beginning_of_month
# => Sun, 01 Dec 2013 
1.9.3p489> date += 1.days until date.wday == 1
# => nil 
1.9.3p489> date
# => Mon, 02 Dec 2013

Answer 2

尝试

date = (Date.current - (1.month)).beginning_of_month    
date = date.next_week unless date.monday?

Answer 3

start = Date.current.beginning_of_month
start.upto(start.next_week).find(&:monday?)
#=> Mon, 06 Jan 2014

Answer 4

您可以使用的方法是

date_in_last_month = Time.now - 1.month

beginning_of_month = date_in_last_month.beginning_of_month

beginning_of_week  = beginning_of_month.beginning_of_week

if beginning_of_week < beginning_of_month
  beginning_of_week + 7.days
else
  beginning_of_week
end

有点长的啰嗦，但有一些代码高尔夫，我认为它可能会做你想要的。

如果您拥有'慢性'宝石，您可以执行以下(credit)

require 'chronic'
date_start = Chronic.parse("Monday of first week of February")

Answer 5

你可以手动完成

date = (Date.current - (1.month)).beginning_of_month
if date.wday != 1
  date = date.end_of_week
  date += date.day 
end

Answer 6

试试这个：

def first_monday(months_before)
  start_of_month = months_before.months.ago.beginning_of_month.to_date
  return start_of_month if start_of_month.monday?
  start_of_month += 8 - start_of_month.cwday
end

first_monday 5
=> Mon, 05 Aug 2013

获取特定月份的第一个起点_周刊

6 个答案: