我用过聚合函数。db.checkins.aggregate([{$match:{checkinType:"Beacon","associationIds.organizationId":"af39bc69-1938-4149","checkinData.time":{"$gte":newDate("2018-01-18T18:30:00.000Z"),"$lt":newDate("2018-01-19T18:30:00.000Z")}}},{"$sort":{"checkinData.time":-1}},{$group:{"_id":{"orgId":"$asst.organizat