Count Documents in GoLang and MongoDB

Create Database

Create a database with the name is learn_mongodb_golang. This database have a collection: Product collection.

/* Create learn_mongodb_golang database */
use learn_mongodb_golang

/* Create Product collection */
db.createCollection('product');

/* Dumping data for `product` collection */
db.getCollection('product').insert({
	"name" : "Mobile 1",
    "price" : 45.0,
    "quantity" : 4.0,
    "status" : true,
    "date" : ISODate("2016-10-20T00:00:00.000Z"),
    "categoryId" : ObjectId("5a30de130867edfa45711668"),
    "brand" : {
        "_id" : new ObjectId(),
        "name" : "brand 1"
    },
    "colors" : [
        "red",
        "green",
        "blue"
    ]
});

db.getCollection('product').insert({
	"name" : "Mobile 2",
    "price" : 12.0,
    "quantity" : 7.0,
    "status" : true,
    "date" : ISODate("2017-11-14T00:00:00.000Z"),
    "categoryId" : ObjectId("5a30de130867edfa45711668"),
    "brand" : {
        "_id" : new ObjectId(),
        "name" : "brand 2"
    },
    "colors" : [
        "yellow",
        "green"
    ]
});

db.getCollection('product').insert({
	"name" : "Mobile 3",
    "price" : 28.0,
    "quantity" : 8.0,
    "status" : true,
    "date" : ISODate("2017-11-20T00:00:00.000Z"),
    "categoryId" : ObjectId("5a30de130867edfa45711668"),
    "brand" : {
        "_id" : new ObjectId(),
        "name" : "brand 3"
    },
    "colors" : [
        "black",
        "blue"
    ]
});

db.getCollection('product').insert({
	"name" : "Laptop 1",
    "price" : 39.0,
    "quantity" : 12.0,
    "status" : false,
    "date" : ISODate("2017-12-26T00:00:00.000Z"),
    "categoryId" : ObjectId("5a30de130867edfa45711669"),
    "brand" : {
        "_id" : new ObjectId(),
        "name" : "brand 1"
    },
    "colors" : [
        "blue"
    ]
});

db.getCollection('product').insert({
	"name" : "Laptop 2",
    "price" : 86.0,
    "quantity" : 23.0,
    "status" : true,
    "date" : ISODate("2017-03-11T00:00:00.000Z"),
    "categoryId" : ObjectId("5a30de130867edfa45711669"),
    "brand" : {
        "_id" : new ObjectId(),
        "name" : "brand 1"
    },
    "colors" : [
        "blue",
        "yellow"
    ]
});

db.getCollection('product').insert({
	"name" : "Tivi 1",
    "price" : 22.0,
    "quantity" : 7.0,
    "status" : true,
    "date" : ISODate("2017-06-26T00:00:00.000Z"),
    "categoryId" : ObjectId("5a30de130867edfa4571166a"),
    "brand" : {
        "_id" : new ObjectId(),
        "name" : "brand 1"
    },
    "colors" : [
        "blue",
        "white",
        "black"
    ]
});

db.getCollection('product').insert({
	"name" : "Tivi 2",
    "price" : 86.0,
    "quantity" : 23.0,
    "status" : false,
    "date" : ISODate("2017-09-24T00:00:00.000Z"),
    "categoryId" : ObjectId("5a30de130867edfa4571166a"),
    "brand" : {
        "_id" : new ObjectId(),
        "name" : "brand 3"
    },
    "colors" : [
        "red",
        "green"
    ]
});

Installing Libraries

Install MGO library as below:

go get gopkg.in/mgo.v2

Configuration

In src folder, create new folder named config. In this folder, create new file named config.go, this file is used to connect to mongodb database:

package config

import (
	mgo "gopkg.in/mgo.v2"
)

func GetMongoDB() (*mgo.Database, error) {
	host := "mongodb://localhost:27017"
	dbName := "learn_mongodb_golang"
	session, err := mgo.Dial(host)
	if err != nil {
		return nil, err
	}
	db := session.DB(dbName)
	return db, nil
}

Entity Classes

Create new folder named entities. In this folder, create new go files as below:

Brand Entity

In entities folder, create new go file named brand_entity.go as below:

package entities

import (
	"fmt"
	"gopkg.in/mgo.v2/bson"
)

type Brand struct {
	Id   bson.ObjectId `bson:"_id"`
	Name string        `bson:"name"`
}

func (this Brand) ToString() string {
	result := fmt.Sprintf("\nbrand id: %s", this.Id.Hex())
	result = result + fmt.Sprintf("\nbrand name: %s", this.Name)
	return result
}

Product Entity

In entities folder, create new go file named product_entity.go as below:

package entities

import (
	"fmt"
	"strings"
	"time"
	"gopkg.in/mgo.v2/bson"
)

type Product struct {
	Id         bson.ObjectId `bson:"_id"`
	Name       string        `bson:"name"`
	Price      float64       `bson:"price"`
	Quantity   int64         `bson:"quantity"`
	Status     bool          `bson:"status"`
	Date       time.Time     `bson:"date"`
	CategoryId bson.ObjectId `bson:"categoryId"`
	Brand      Brand         `bson:"brand"`
	Colors     []string      `bson:"colors"`
}

func (this Product) ToString() string {
	result := fmt.Sprintf("id: %s", this.Id.Hex())
	result = result + fmt.Sprintf("\nname: %s", this.Name)
	result = result + fmt.Sprintf("\nprice: %0.1f", this.Price)
	result = result + fmt.Sprintf("\nquantity: %d", this.Quantity)
	result = result + fmt.Sprintf("\nstatus: %t", this.Status)
	result = result + fmt.Sprintf("\ndate: %s", this.Date.Format("2006-01-02"))
	result = result + fmt.Sprintf("\ncategory id: %s", this.Category.Hex())
	result = result + this.Brand.ToString()
	result = result + fmt.Sprintf("\ncolors: %s", strings.Join(this.Colors, ", "))
	return result
}

Models

In src folder, create new folder named models. In models folder, create new file named product_model.go. This file contains methods to interact with the database.

package models

import (
	"config"
)

type ProductModel struct {
}

func (this ProductModel) Count() (int, error) {
	db, err := config.GetMongoDB()
	if err != nil {
		return 0, err
	} else {
		return db.C("product").Count()
	}
}

Structure of Project

Run Application

In src folder, create new file named main.go and use command go run main.go run application:

package main

import (
	"fmt"
	"models"
)

func main() {
	var productModel models.ProductModel
	result, err := productModel.Count()
	if err != nil {
		fmt.Println(err)
	} else {
		fmt.Println("Count Entities: ", result)
	}
}

Output

Count Entities:  7