使用mgo驱动程序的mongo聚合查询

package main

import (
    "fmt"
    "gopkg.in/mgo.v2"
    "gopkg.in/mgo.v2/bson"
)

type Order struct {
    ID     bson.ObjectId `bson:"_id,omitempty"`
    UserID bson.ObjectId `bson:"user_id"`
    Amount float64       `bson:"amount"`
    Date   time.Time     `bson:"date"`
}

func main() {
    session, err := mgo.Dial("mongodb://localhost:27017")
    if err != nil {
        panic(err)
    }
    defer session.Close()

    c := session.DB("test").C("orders")

    pipeline := []bson.M{
        {"$match": bson.M{"date": bson.M{"$gte": time.Now().Add(-24 * time.Hour)}}},
        {"$group": bson.M{
            "_id": "$user_id",
            "total_amount": bson.M{"$sum": "$amount"},
        }},
        {"$sort": bson.M{"total_amount": -1}},
        {"$limit": 10},
    }

    var results []bson.M
    err = c.Pipe(pipeline).All(&results)
    if err != nil {
        panic(err)
    }

    for _, result := range results {
        fmt.Printf("User ID: %s, Total Amount: %.2f\n", result["_id"], result["total_amount"])
    }
}