MongoClient の作成

uri := os.Getenv("MONGODB_URI")

MONGODB_URI=mongodb+srv://<db_username>:<db_password>@<cluster-url>?retryWrites=true&w=majority

// Connects to MongoDB and sets a Stable API version
package main
import (
	"context"
	"fmt"
	"log"
	"os"
	"go.mongodb.org/mongo-driver/v2/bson"
	"go.mongodb.org/mongo-driver/v2/mongo"
	"go.mongodb.org/mongo-driver/v2/mongo/options"
)
func main() {
	var uri string
	if uri = os.Getenv("MONGODB_URI"); uri == "" {
		log.Fatal("You must set your 'MONGODB_URI' environment variable. See\n\t https://mongodb.com/ja-jp/docs/drivers/go/current/usage-examples/")
	}
	// Uses the SetServerAPIOptions() method to set the Stable API version to 1
	serverAPI := options.ServerAPI(options.ServerAPIVersion1)
	// Defines the options for the MongoDB client
	opts := options.Client().ApplyURI(uri).SetServerAPIOptions(serverAPI)
	// Creates a new client and connects to the server
	client, err := mongo.Connect(opts)
	if err != nil {
		panic(err)
	}
	defer func() {
		if err = client.Disconnect(context.TODO()); err != nil {
			panic(err)
		}
	}()
	// Sends a ping to confirm a successful connection
	var result bson.M
	if err := client.Database("admin").RunCommand(context.TODO(), bson.D{{"ping", 1}}).Decode(&result); err != nil {
		panic(err)
	}
	fmt.Println("Pinged your deployment. You successfully connected to MongoDB!")
}