foo_array.sort_by { |f| [f.end_date.nil? ? 0 : 1, f.end_date.to_i, f.start_date.to_i] }.reverse

• 零三元组将确保这些是第一个
• 将end_date / start_date转换为整数将确保它们的顺序
• 那么调用reverse将给予降序

如果您可以执行SQL查询，那么下面的代码应该对您有效。

Foo.order('start_date IS NOT NULL, start_date DESC')

另一方面，如果您已经有了物化数组，则可以执行以下操作。

arr = Array of Foos
arr.sort_by { |a, b| a.start_date && b.start_date ? a.start_date <=> b.start_date : a.start_date ? 1 : -1 }

对end_date重复相同的过程

使用#sort的单遍
a）使用块排序

# Using sort method
sorted = entries.sort do |a,b|
  # 1, 0 , -1 or nil
  comparison_result = a.end_date <=> b.end_date

  if comparison_result.nil?
    # nil follows a date
    a.end_date.nil? ? 1 : -1
  elsif comparison_result.zero?
    # end_dates are equal, compare start_dates instead
    a.start_date <=> b.start_date
  else
      comparison_result
  end.* -1 # descending order
end

B）将自定义比较方法添加到您的模型或模块中，然后执行以下操作

sorted = entries.sort do |a,b|
    a.compare_using_dates b
end

class Foo
  def compare_using_dates(other)
    comparison_result = end_date <=> other.end_date

    # nil result means one of the records has a nil end_date, so the end_dates are not equal
    if comparison_result.nil?
      end_date.nil? ? 1 : -1
    elsif comparison_result.zero?
      # end_dates are equal, compare start_dates instead
      start_date <=> other.start_date
    else
      comparison_result
    end.* -1
  end
end