Use Struct Tags

You can specify the way that the Go Driver converts Go structs to BSON by using struct tags.

Example

Tip

Read the Usage Examples to learn how to run this example.

The following code declares a struct of type BlogPost. This struct contains a struct tag that maps the WordCount field to the BSON field name word_count. By default, the driver marshals the other fields as the lowercase of the struct field name:

// Specifies struct tags on a struct by using the Go driver
package main
import (
	"context"
	"fmt"
	"log"
	"os"
	"github.com/joho/godotenv"
	"go.mongodb.org/mongo-driver/v2/mongo"
	"go.mongodb.org/mongo-driver/v2/mongo/options"
)
// Specifies a different name for RestaurantID
// and marks certain fields as omitempty
type Restaurant struct {
	Name         string
	RestaurantId string        `bson:"restaurant_id,omitempty"`
	Cuisine      string        `bson:"cuisine,omitempty"`
	Address      interface{}   `bson:"address,omitempty"`
	Borough      string        `bson:"borough,omitempty"`
	Grades       []interface{} `bson:"grades,omitempty"`
}
func main() {
	if err := godotenv.Load(); err != nil {
		log.Println("No .env file found")
	}
	var uri string
	if uri = os.Getenv("MONGODB_URI"); uri == "" {
		log.Fatal("You must set your 'MONGODB_URI' environment variable. See\n\t https://www.mongodb.com/docs/drivers/go/current/usage-examples/#environment-variable")
	}
	client, err := mongo.Connect(options.Client().ApplyURI(uri))
	if err != nil {
		panic(err)
	}
	defer func() {
		if err = client.Disconnect(context.TODO()); err != nil {
			panic(err)
		}
	}()
	coll := client.Database("sample_restaurants").Collection("restaurants")
	// Creates a Restaurant document
	newRestaurant := Restaurant{
		Name:         "Amazing Pizza",
		RestaurantId: "123456789",
		Cuisine:      "American",
	}
	// Inserts the sample document describing a restaurant into the collection
	result, err := coll.InsertOne(context.TODO(), newRestaurant)
	if err != nil {
		panic(err)
	}
	// Prints the ID of the inserted document
	fmt.Printf("Document inserted with ID: %s\n", result.InsertedID)
	// When you run this file, it should print:
	// Document inserted with ID: ObjectID("...")
}

The following example creates a BlogPost instance and inserts it into the posts collection. During the insert operation, the driver interprets the struct tag to marshal the WordCount struct field as word_count:

Tip

Read the Usage Examples to learn how to run this example.

// Specifies struct tags on a struct by using the Go driver
package main
import (
	"context"
	"fmt"
	"log"
	"os"
	"github.com/joho/godotenv"
	"go.mongodb.org/mongo-driver/v2/mongo"
	"go.mongodb.org/mongo-driver/v2/mongo/options"
)
// Specifies a different name for RestaurantID
// and marks certain fields as omitempty
type Restaurant struct {
	Name         string
	RestaurantId string        `bson:"restaurant_id,omitempty"`
	Cuisine      string        `bson:"cuisine,omitempty"`
	Address      interface{}   `bson:"address,omitempty"`
	Borough      string        `bson:"borough,omitempty"`
	Grades       []interface{} `bson:"grades,omitempty"`
}
func main() {
	if err := godotenv.Load(); err != nil {
		log.Println("No .env file found")
	}
	var uri string
	if uri = os.Getenv("MONGODB_URI"); uri == "" {
		log.Fatal("You must set your 'MONGODB_URI' environment variable. See\n\t https://www.mongodb.com/docs/drivers/go/current/usage-examples/#environment-variable")
	}
	client, err := mongo.Connect(options.Client().ApplyURI(uri))
	if err != nil {
		panic(err)
	}
	defer func() {
		if err = client.Disconnect(context.TODO()); err != nil {
			panic(err)
		}
	}()
	coll := client.Database("sample_restaurants").Collection("restaurants")
	// Creates a Restaurant document
	newRestaurant := Restaurant{
		Name:         "Amazing Pizza",
		RestaurantId: "123456789",
		Cuisine:      "American",
	}
	// Inserts the sample document describing a restaurant into the collection
	result, err := coll.InsertOne(context.TODO(), newRestaurant)
	if err != nil {
		panic(err)
	}
	// Prints the ID of the inserted document
	fmt.Printf("Document inserted with ID: %s\n", result.InsertedID)
	// When you run this file, it should print:
	// Document inserted with ID: ObjectID("...")
}

View a fully runnable example.

Expected Result

After you run the full example, you can find the following document in the posts collection:

{
    "_id" : ObjectId("..."),
    "title" : "Annuals vs. Perennials?",
    "author" : "Sam Lee",
    "word_count" : 682,
    "lastupdated": ...,
    "tags" : ["seasons", "gardening", "flower"]
}

For an example on how to find a document, see Find Documents.

Additional Information

To learn more about using struct tags, converting to/from BSON, and handling potential errors, see working with BSON.

API Documentation

MongoDB Go Driver