* 定义快速按时间查询的便利方法
  
** 问题

   对于按照时间范围查询的需求，一般需要构造一个表示时间范围的 Range 对象，例如：

   #+BEGIN_SRC ruby
     Student.where(created_at: Time.now.beginning_of_day..Time.now.end_of_day)
   #+END_SRC

   或者

   #+BEGIN_SRC ruby
     Student.where(created_at: Time.new(2016, 1, 1)..Time.new(2016, 12, 31))
   #+END_SRC

** 定义一个便利方法
  
   为了简化构造时间 Range 对象的过程，我们可以定义一个便利方法，例如：

   创建一个文件 =~/.arql.d/date_range.rb= ，内容如下：

   #+BEGIN_SRC ruby
     module Kernel
    
       # == Example:
       #  Range
       #    1. -3..0
       #    2. '27'..'29'
       #    3. '04-01'..'04-10'
       #    4. '2021-04-01'..'2021-04-10'
       #  Array
       #    1. [nil, nil] or [] => 1970-01-01 ~ 1000 days later from now
       #    2. [:yday, :today] or [:yesterday, :today]
       #    3. [-10.months, :today]
       #  Others
       #    1. Time.now or Date.today
       #    2. :now or :today
       #    3. :yesterday or :yday
       #    4. -2
       #    5. -2.months
       def dates_range(dates)
         dates = :yesterday if dates == :yday
         if dates.is_a?(Range)
           s = if dates.begin.is_a?(Integer)
                 (Time.now+dates.begin.days).beginning_of_day
               elsif dates.begin.is_a?(String) && dates.begin =~ /^\d{4}-\d{2}-\d{2}$/
                 Time.parse(dates.begin).beginning_of_day
               elsif dates.begin.is_a?(String) && dates.begin =~ /^\d{2}-\d{2}$/
                 Time.strptime(dates.begin, '%m-%d').beginning_of_day
               elsif dates.begin.is_a?(String) && dates.begin =~ /^\d{2}$/
                 Time.strptime(dates.begin, '%d').beginning_of_day
               else
                 dates.begin
               end
           e = if dates.end.is_a?(Integer)
                 (Time.now+dates.end.days).end_of_day
               elsif dates.end.is_a?(String) && dates.end =~ /^\d{4}-\d{2}-\d{2}$/
                 Time.parse(dates.end).end_of_day
               elsif dates.end.is_a?(String) && dates.end =~ /^\d{2}-\d{2}$/
                 Time.strptime(dates.end, '%m-%d').end_of_day
               elsif dates.end.is_a?(String) && dates.end =~ /^\d{2}$/
                 Time.strptime(dates.end, '%d').end_of_day
               else
                 dates.end
               end
           s..e
         elsif dates.is_a?(Array)
           if dates.size == 2
             s = dates.first || Date.new(1970, 1, 1)
             s = if s.is_a?(Time) || s.is_a?(Date)
                   s.beginning_of_day
                 elsif s == :now
                   Time.now.beginning_of_day
                 elsif s == :today
                   Date.today.beginning_of_day
                 elsif s == :yesterday || s == :yday
                   Date.yesterday.beginning_of_day
                 elsif s.in?(Time.instance_methods)
                   Time.now.send(s).beginning_of_day
                 elsif s.is_a?(ActiveSupport::Duration)
                   (Time.now+s).beginning_of_day
                 elsif s.is_a?(Integer)
                   (Time.now+s.days).beginning_of_day
                 else
                   raise "Not supported s: #{s}"
                 end
             e = dates.last || Date.today + 1000.days
             e = if e.is_a?(Time) || e.is_a?(Date)
                   e.end_of_day
                 elsif e == :now
                   Time.now.end_of_day
                 elsif e == :today
                   Date.today.end_of_day
                 elsif e == :yesterday || e == :yday
                   Date.yesterday.end_of_day
                 elsif e.in?(Time.instance_methods)
                   Time.now.send(e).end_of_day
                 elsif e.is_a?(ActiveSupport::Duration)
                   (Time.now+e).end_of_day
                 elsif e.is_a?(Integer)
                   (Time.now+e.days).beginning_of_day
                 else
                   raise "Not supported e: #{e}"
                 end
             return s..e
           else
             times = dates.map do |date|
               if date.nil?
                 nil
               elsif date.is_a?(Time)
                 date
               elsif date == :now
                 Time.now
               elsif date.in?(Time.instance_methods)
                 Time.now.send(date)
               elsif date.is_a?(ActiveSupport::Duration)
                 Time.now+date
               elsif date.is_a?(Integer)
                 (Time.now+date.days).beginning_of_day
               else
                 raise "Not supported date: #{date}"
               end
             end
             s = times.first || Time.new(1970, 1, 1, 0, 0, 0)
             e = times.last || Time.now + 1000.days
             return s..e
           end
         else
           if dates.is_a?(Time) or dates.is_a?(Date)
             dates = dates.beginning_of_day..dates.end_of_day
           elsif dates == :now
             dates = Time.now.beginning_of_day..Time.now.end_of_day
           elsif dates == :today
             dates = Date.today.beginning_of_day..Date.today.end_of_day
           elsif dates == :yday || dates == :yesterday
             dates = Date.yesterday.beginning_of_day..Date.yesterday.end_of_day
           elsif dates.in?(Time.instance_methods)
             dates = Time.now.send(dates).beginning_of_day..Time.now.send(dates).end_of_day
           elsif dates.is_a?(ActiveSupport::Duration)
             dates = (Time.now+dates).beginning_of_day..(Time.now+dates).end_of_day
           elsif dates.is_a?(Integer)
             (Time.now+dates.days).beginning_of_day..(Time.now+dates.days).end_of_day
           else
             raise "Not supported dates: #{dates}"
           end
         end
       end
    
       alias_method :dates, :dates_range
     end
    
     class ::ArqlModel
    
       class << self
         def ts_attribute_for_create
           (timestamp_attributes_for_create||[]).find { |e| e.in?(column_names) }
         end
    
         def ts_attribute_for_update
           (timestamp_attributes_for_update||[]).find { |e| e.in?(column_names) }
         end
    
    
         def created_on(dates)
           attr = ts_attribute_for_create
           raise 'No attrtibute for create defined' unless attr
           where(attr => dates_range(dates))
         end
    
         alias on created_on
    
         def today
           created_on(0)
         end
    
         def modified_on(dates)
           attr = ts_attribute_for_update
           raise 'No attrtibute for update defined' unless attr
           where(attr: dates_range(dates))
         end
       end
     end
   #+END_SRC
  
   然后在 =~/.arql.d/init.rb= 中引入这个文件:

   #+BEGIN_SRC ruby
     load(File.absolute_path(File.dirname(__FILE__) + "/date_range.rb"))
   #+END_SRC

  
** 使用方法

   然后就可以使用这个方法了:

   #+BEGIN_SRC ruby
     Student.where(created_at: dates(0)). # 查询今天创建的
     Student.where(created_at: dates(:today)). # 查询今天创建的
     Student.where(created_at: dates('2016-01-01'..'2016-01-31')) # 查询 2016 年 1 月创建的
     Student.where(created_at: dates('01'..'10'))  # 查询当月 1-10 号创建的
     Student.where(created_at: dates('03-01'..'04-10'))  # 查询当年 3 月 1 日到 4 月 10 日创建的
     Student.where(created_at: dates(-20..-1))  # 查询 20 天前到昨天创建的
   #+END_SRC

   如果是对 created_at 字段 (在 =init.yaml= 中通过 =created_at= 配置，默认值是 =created_at=) 进行查询, 可以直接使用:

   #+BEGIN_SRC ruby
     Student.on(0). # 查询今天创建的
     Student.on(:today). # 查询今天创建的
     Student.on('2016-01-01'..'2016-01-31') # 查询 2016 年 1 月创建的
     Student.on('01'..'10')  # 查询当月 1-10 号创建的
     Student.on('03-01'..'04-10')  # 查询当年 3 月 1 日到 4 月 10 日创建的
     Student.on(-20..-1)  # 查询 20 天前到昨天创建的
   #+END_SRC