您可以使用聚合框架来实现所需的功能：
db.collection.aggregate([ // Get only records created in the last 30 days {$match:{ "createdTimestamp":{$gt: new Date(ISODate().getTime() - 1000*60*60*24*30)} }}, // Get the year, month and day from the createdTimeStamp {$project:{ "year":{$year:"$createdTimestamp"},"month":{$month:"$createdTimestamp"},"day": {$dayOfMonth:"$createdTimestamp"} }}, // Group by year, month and day and get the count {$group:{ _id:{year:"$year", month:"$month", day:"$day"},"count":{$sum:1} }}])
