mongoid 如何 使用 mongoDB aggregate功能 💋

mongoid_aggregate.rb

class User
  include Mongoid::Document
  include Mongoid::Timestamps

  def self.added_fans(day_num)

    self.collection.aggregate(
      {
        "$match" => {
          "followable_type" => "User",
           "created_at" => {
              "$gte" => yesterday.to_i.days.ago.beginning_of_day, # 大于等于 昨天的开始时间
              "$lte" => Date.yesterday.end_of_day # 小于等于 昨天的结束的时间
           }
        }
      }, # 查询条件
      {
        "$group" => {
          _id: "$follow_id", # 根据 follow_id 分组统计
          matches: { "$sum" => 1 } # 统计数量
        }
      },
      {
        "$sort" => { matches: -1 } #倒序
      },
      {
        "$limit" => 10
      }
    )
  end

end