问两个等间隔Rails的DateTime对象间的数据检索

EN

a = DateTime.new(2014) # Wed, 01 Jan 2014 00:00:00 +0000
b = DateTime.new(2015) # Thu, 01 Jan 2015 00:00:00 +0000
diff = b.to_i - a.to_i # in seconds.
puts "2014 has #{ (diff / 1.day).round } days"

puts "a tenth into 2014 is #{ a + (diff / 10).seconds }"

Foo.where(created_at: a..(a + (diff / 10).seconds))

class Foo < ActiveRecord::Base

    # Get the maximum value of bar column 
    #   for divided into periods between a start and end date.
    # @param start [DateTime]
    # @param finish [DateTime]
    # @param divisor [Integer] the number of parts to split into
    # @return array 
    #   will always have divisor number of elements
    #   elements may be empty 
    def maximum_bar_values_for_period(start, finish, divisor = 10)
        diff = finish.to_i - start.to_i
        part = diff / divisor
        (0..divisor).map do |i|
            start_period = start + ((i - 1) * part).seconds
            end_peroid =  start_period + part.seconds
            Foo.where(created_at: start_period..end_peroid).maximum(:bar)
        end
    end
end