使用mongo-driver实现Golang mongodb聚合

import (
    "context"
    "go.mongodb.org/mongo-driver/mongo"
    "go.mongodb.org/mongo-driver/mongo/options"
)

client, err := mongo.Connect(context.TODO(), options.Client().ApplyURI("mongodb://localhost:27017"))
if err != nil {
    // 处理连接错误
}

collection := client.Database("mydb").Collection("mycollection")

pipeline := []bson.M{
    {
        "$group": bson.M{
            "_id":   "$field1",
            "count": bson.M{"$sum": 1},
        },
    },
    {
        "$sort": bson.M{
            "count": -1,
        },
    },
}

cursor, err := collection.Aggregate(context.TODO(), pipeline)
if err != nil {
    // 处理聚合错误
}
defer cursor.Close(context.TODO())

for cursor.Next(context.TODO()) {
    var result bson.M
    err := cursor.Decode(&result)
    if err != nil {
        // 处理解码错误
    }
    
    // 处理聚合结果
}
if err := cursor.Err(); err != nil {
    // 处理游标错误
}