An example of manipulate data in mongodb with golang

user.go

package main

import (
	"context"
	"log"
	"time"

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

func check(err error) {
	if err != nil {
		log.Fatal(err)
	}
}

// User defines an entity for our database
type User struct {
	Name string `bson:"name"`
	ID   int32  `bson:"ID"`
	Age  int16  `bson:"age"`
}

// UserRepository defines a store for manipulate data
type UserRepository struct {
	ctx        context.Context
	collection *mongo.Collection
}

// InsertOne inserts a user struct
func (ur *UserRepository) InsertOne(user User) error {
	_, err := ur.collection.InsertOne(ur.ctx, user)
	// log.Print(result)
	return err
}

// FindOneByID returns a user struct and error
func (ur *UserRepository) FindOneByID(id int16) (User, error) {
	var r User
	filter := bson.M{"ID": id}
	err := ur.collection.FindOne(ur.ctx, filter).Decode(&r)
	return r, err
}

// FindAgeSmallerThan demonstrates an array in return from mongo query
func (ur *UserRepository) FindAgeSmallerThan(age int16) ([]*User, error) {
	var results []*User

	filter := bson.M{"age": bson.M{"$lt": 6}}
	cursor, err := ur.collection.Find(ur.ctx, filter)
	if err != nil {
		return results, err
	}

	for cursor.Next(ur.ctx) {
		var user User
		err := cursor.Decode(&user)
		check(err)
		results = append(results, &user)
	}
	if err := cursor.Err(); err != nil {
		return results, cursor.Err()
	}

	return results, nil
}

func main() {
	// Connect to database
	client, err := mongo.NewClient(options.Client().ApplyURI("mongodb://localhost:27017"))
	check(err)

	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	err = client.Connect(ctx)
	defer cancel()

	// process users collection
	collection := client.Database("test").Collection("users")

	repo := UserRepository{ctx: ctx, collection: collection}

	// Insert user
	err = repo.InsertOne(User{Name: "foo", ID: 1, Age: 10})
	check(err)

	// Find user by ID field
	user, err := repo.FindOneByID(1)
	check(err)
	log.Print(user)

}