通过mongo-go-driver使用mongodb本机函数

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

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

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

pipeline := bson.A{
    bson.D{{"$function", bson.D{
        {"body", "function() { return 'Hello, World!'; }"},
        {"args", bson.A{}},
        {"lang", "js"},
    }}},
    bson.D{{"$project", bson.D{
        {"_id", 0},
        {"result", bson.D{{"$functionResult"}}},
    }}},
}

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

for cursor.Next(context.TODO()) {
    var result struct {
        Result string `bson:"result"`
    }
    err := cursor.Decode(&result)
    if err != nil {
        // 处理错误
    }
    // 处理结果
    fmt.Println(result.Result)
}