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Learn Nodemailer Module in Node.js

In this tutorial, we will learn how to send email in Node.js using the nodemailer npm package.For the email provider, we are going to use Sendinblue. Prerequisites Node.js (>v6.0.0 for nodemailer module) Code Editor (For Ex. VS Code, Atom) An account in SendinblueStart by creating a free account in Sendinblue. A Sendinblue free account offers 300 mails/day. Its setup is easy and straightforward. An introduction to Nodemailer Nodemailer, an open source project started in 2010, is annpm module for Node.js applications to send emails. Today, nodemailer is a de facto to send an email in Node.js. Highlights of Nodemailer It is a single module with zero dependencies  It supports HTML Content  Allows you to easily add attachments to messages Supports SMTP as default transport method; other supported transport methods are SES, Sendmail, Stream. OAuth2 authenticationGetting Started For this tutorial, I am using Nodejs v12.16.1 and VS Code as the Code Editor. Create a new directory nodemailer-example.  Open the terminal or cmd inside the directory and run  $ npminit --yes It will initialize a new npm package. Install dependencies Following different npm packages, we are going to use in this project. nodemailer – To send the mail express – To create APIs cors – To resolve the cross originresource sharing body-parser – To extract the body from the API request dotenv – To access the environment variables $ npm install --save nodemailer express cors body-parser dotenv This command will install all the dependencies. Now, we can start the coding. Project Structure Open the nodemailer-example in the code editor and create the following folders and files in it; not to worry, I will be explaining all the files and commands involved.  nodemailer-example  |- routes  |- mail-api.js  |- src  |- send-mail.js    |- template      |- mail.html  |- .env  |- index.js Sendinmail Setup Login to your Sendinmail account. From the top-left menu, select SMTP & API. Select the SMTP tab. Click on Create a new SMTP key. Copy the key at some safe place.  You can deactivate the SMTP key anytime. Now, open the .env file and create 2 key-value pair. USER=YOUREMAILADDRESS  PASS=xxxxxxx-xxxxxxxxxxxx-xxxxxxxxxxxxxxxxxxxxxx USER: The email address using which you created the sendinmail account. PASS:SMTP Key By using .env file we are not exposing the credentials to the web.  Using environment variables in the project is an industrial standard.  Source Code Open the send-mail.js in the editor. Copy and paste the below code in it."use strict";  require("dotenv").config();  constnodemailer = require("nodemailer");  /**  * sendEmail  * @param{Object}mailObj - Email information  * @param{String}from- Email address of the sender  * @param{Array}to- Array of recipients email address  * @param{String}subject - Subject of the email  * @param{String}text - Email body  */  constsendEmail = async (mailObj) => {  const{ from, to, subject, text } = mailObj;  try {  // Create a transporter  lettransporter = nodemailer.createTransport({  host:"smtp-relay.sendinblue.com",  port:587,  auth: {  user:process.env.USER,  pass:process.env.PASS,  },  });  // send mail with defined transport object  letinfo = awaittransporter.sendMail({  from:from, // sender address  to:to, // list of receivers  subject:subject, // subject line  text:text, // plain text body  });  console.log(`Message sent: ${info.messageId}`);  return`Message sent: ${info.messageId}`;  } catch (error) {  console.error(error);  thrownewError(  `Something went wrong in the sendmail method. Error: ${error.message}`  );  }  };  module.exports = sendEmail; Code Walk Through In the beginning, we are importing dotenv to get the environment variables from the .env file and nodemailer to send the email. The sendEmailfunction accepts an object. This object has from, to, subject, text fields. Please note that, from and USER must be same. The nodemailer.createTransportreturns a mail object. The transporter variable is storing the mail object.  let transporter = nodemailer.createTransport({ host: "smtp-relay.sendinblue.com", port: 587, auth: { user: process.env.USER, pass: process.env.PASS, }, });Open SMTP tab in your sendinmail account and cross check the host and port.In the auth object, we are passing the user and password from the environment variable.Send the mail using sendMail method.// send mail with defined transport object let info = await transporter.sendMail({ from: from, // sender address to: to, // list of receivers subject: subject, // Subject line text: text, // plain text body });It returns a Promise of Send Message Info. In the end, it is returning the message id.  Express Route The sendEmail method is ready.  Let’s create an express route for it. This is the API endpoint using which we can access the sendEmail function. Open the mail-api.js in the code editor and paste the below code. constexpress = require("express");  constrouter = express.Router();  constsendMailMethod = require("../src/send-mail");  // Post request to send an email  router.post("/sendmail", async (req, res) => {  try {  constresult = awaitsendMailMethod(req.body);  // send the response  res.json({  status:true,  payload:result  });  } catch (error) {  console.error(error.message);  res.json({  status:false,  payload:"Something went wrong in Sendmail Route."  })  }  }) module.exports = router; The express framework provides a Router method to create different HTTP methods. Here, we have created a POST method to send the mail.  Instead of extracting the req.body parameters, we passed it as it is. The benefit of this approach is that if there is a change in argument or position, then we would not have to change it in all the places.  In the end, we are exporting the router. Now, this can be used in the server side. Express Server Now, it’s time to create a server and expose the routes on it. Open the index.js and paste the below code in it. "use strict";  constexpress = require("express");  constbodyParser = require("body-parser");  constcors = require("cors");  constapp = express();  constmailAPI = require("./routes/mail-api.js");  // Express body parser  app.use(cors());  app.use(bodyParser.json());  app.use(  bodyParser.urlencoded({  limit:"50mb",  extended:false,  parameterLimit:50000  })  );  // use the routes specified in route folder  app.use("/api/v1", mailAPI);  constport = process.env.PORT || 4444;  //listen to the server  app.listen(port, function () {  console.log(`listening to the port ${port} .....`);  }); The route is available on /api/v1/sendmail. Run the server. $ node index.js  listening to the port 4444 ..... Send an Email using API There are couple of methods to test the API. Using the Postmanor using the Curl command. Using Postman Install Postman on your machine if it is not installed. Create a POST request. URL: http://localhost:4444/api/v1/sendmail Content Type: JSON – Body tab > select JSON from dropdown Request Body:  {  "from": "hello@schadokar.dev",  "to": ["shubham@schadokar.dev"],  "subject": "Mail from Nodemailer",  "text": "Sending an email using nodemailer package."  } Hit Send. Make sure the server is running. On Success, the response returns the message id. Now, check your mailbox. If you are unable to find the mail in your Inbox, check the promotional mail folder. Using Curl CommandOpen the terminal or cmd.In the below curl command, change the parameters and enter.curl -X POST http://localhost:4444/api/v1/sendmail -H "Content-Type:application/json" -d '{"from": "hello@schadokar.dev","to": ["shubham@schadokar.dev"],"subject": "Mail from Nodemailer", "text": "Sending an email using nodemailer package."}'In this example, we have sent a simple text message to the recipient.  Nodemailer also gives you an option to send the message in HTML format. Mail template Open the mail.html in the code editor and paste the below code. <div style="text-align: center;""> <h1 style="color: #3584c8;">Nodemailer Example</h1> <p> This is an example html template to demonstrate the sending email using html. <br />

Learn Nodemailer Module in Node.js

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Learn Nodemailer Module in Node.js

In this tutorial, we will learn how to send email in Node.js using the nodemailer npm package.

For the email provider, we are going to use Sendinblue

Prerequisites 

  • Node.js (>v6.0.0 for nodemailer module) 
  • Code Editor (For Ex. VS Code, Atom) 
  • An account in Sendinblue

Start by creating a free account in Sendinblue

A Sendinblue free account offers 300 mails/day. Its setup is easy and straightforward. 

An introduction to Nodemailer 

Nodemailer, an open source project started in 2010, is annpm module for Node.js applications to send emails. Today, nodemailer is a de facto to send an email in Node.js. 

Highlights of Nodemailer 

  • It is a single module with zero dependencies  
  • It supports HTML Content  
  • Allows you to easily add attachments to messages 
  • Supports SMTP as default transport method; other supported transport methods are SES, Sendmail, Stream. 
  • OAuth2 authentication

Getting Started 

For this tutorial, I am using Nodejs v12.16.1 and VS Code as the Code Editor. 

Create a new directory nodemailer-example.  

Open the terminal or cmd inside the directory and run  

$ npminit --yes 

It will initialize a new npm package. 

Install dependencies 

Following different npm packages, we are going to use in this project. 

  • nodemailer – To send the mail 
  • express – To create APIs 
  • cors – To resolve the cross originresource sharing 
  • body-parser – To extract the body from the API request 
  • dotenv – To access the environment variables 
$ npm install --save nodemailer express cors body-parser dotenv 

This command will install all the dependencies. Now, we can start the coding. 

Project Structure 

Open the nodemailer-example in the code editor and create the following folders and files in it; not to worry, I will be explaining all the files and commands involved.  

nodemailer-example 
  |- routes 
    |- mail-api.js 
  |- src 
    |- send-mail.js 
  |- template 
    |- mail.html 
  |- .env 
  |- index.js 

Sendinmail Setup 

  • Login to your Sendinmail account. 
  • From the top-left menu, select SMTP & API. 
  • Select the SMTP tab. 
  • Click on Create a new SMTP key. Copy the key at some safe place.  
  • You can deactivate the SMTP key anytime. 
  • Now, open the .env file and create 2 key-value pair. 
USER=YOUREMAILADDRESS 
PASS=xxxxxxx-xxxxxxxxxxxx-xxxxxxxxxxxxxxxxxxxxxx 
  • USERThe email address using which you created the sendinmail account. 
  • PASS:SMTP Key 

By using .env file we are not exposing the credentials to the web.  

Using environment variables in the project is an industrial standard.  

Source Code 

  • Open the send-mail.js in the editor. 
  • Copy and paste the below code in it.
"use strict"; 
require("dotenv").config(); 
constnodemailer = require("nodemailer"); 
/** 
 * sendEmail 
 * @param{Object}mailObj - Email information 
 * @param{String}from- Email address of the sender 
 * @param{Array}to- Array of recipients email address 
 * @param{String}subject - Subject of the email 
 * @param{String}text - Email body 
 */ 
constsendEmail = async (mailObj) => { 
const{ from, to, subject, text } = mailObj; 
try { 
// Create a transporter 
lettransporter = nodemailer.createTransport({ 
host:"smtp-relay.sendinblue.com", 
port:587, 
auth: { 
user:process.env.USER, 
pass:process.env.PASS, 
      }, 
    }); 
// send mail with defined transport object 
letinfo = awaittransporter.sendMail({ 
from:from, // sender address 
to:to, // list of receivers 
subject:subject, // subject line 
text:text, // plain text body 
    }); 
console.log(`Message sent: ${info.messageId}`); 
return`Message sent: ${info.messageId}`; 
  } catch (error) { 
console.error(error); 
thrownewError( 
`Something went wrong in the sendmail method. Error: ${error.message}` 
    ); 
  } 
}; 
module.exports = sendEmail; 

Code Walk Through 

In the beginning, we are importing dotenv to get the environment variables from the .env file and nodemailer to send the email. 

The sendEmailfunction accepts an object. This object has from, to, subject, text fields. 

Please note that, from and USER must be same. 

The nodemailer.createTransportreturns a mail object. The transporter variable is storing the mail object. 

 let transporter = nodemailer.createTransport({
      host: "smtp-relay.sendinblue.com",
      port: 587,
      auth: {
        user: process.env.USER,
        pass: process.env.PASS,
      },
    });

Open SMTP tab in your sendinmail account and cross check the host and port.

In the auth object, we are passing the user and password from the environment variable.

Send the mail using sendMail method.

// send mail with defined transport object
    let info = await transporter.sendMail({
      from: from, // sender address
      to: to, // list of receivers
      subject: subject, // Subject line
      text: text, // plain text body
    });

It returns a Promise of Send Message Info. 

In the end, it is returning the message id.  

Express Route 

The sendEmail method is ready.  

Let’s create an express route for it. This is the API endpoint using which we can access the sendEmail function. 

Open the mail-api.js in the code editor and paste the below code. 

constexpress = require("express"); 
constrouter = express.Router(); 
constsendMailMethod = require("../src/send-mail"); 
// Post request to send an email 
router.post("/sendmail", async (req, res) => { 
try { 
constresult = awaitsendMailMethod(req.body); 
// send the response 
res.json({ 
status:true, 
payload:result 
        }); 
    } catch (error) { 
console.error(error.message); 
res.json({ 
status:false, 
payload:"Something went wrong in Sendmail Route." 
        }) 
    } 
}) 
module.exports = router; 

The express framework provides a Router method to create different HTTP methods. Here, we have created a POST method to send the mail.  

Instead of extracting the req.body parameters, we passed it as it is. The benefit of this approach is that if there is a change in argument or position, then we would not have to change it in all the places.  

In the end, we are exporting the router. Now, this can be used in the server side. 

Express Server 

Now, it’s time to create a server and expose the routes on it. 

Open the index.js and paste the below code in it. 

"use strict"; 
constexpress = require("express"); 
constbodyParser = require("body-parser"); 
constcors = require("cors"); 
constapp = express(); 
constmailAPI = require("./routes/mail-api.js"); 
// Express body parser 
app.use(cors()); 
app.use(bodyParser.json()); 
app.use( 
bodyParser.urlencoded({ 
limit:"50mb", 
extended:false, 
parameterLimit:50000 
  }) 
); 
// use the routes specified in route folder 
app.use("/api/v1", mailAPI); 
constport = process.env.PORT || 4444; 
//listen to the server 
app.listen(port, function () { 
console.log(`listening to the port ${port} .....`); 
}); 

The route is available on /api/v1/sendmail. 

Run the server. 

$ node index.js 
listening to the port 4444 ..... 

Send an Email using API 

There are couple of methods to test the API. 

Using the Postmanor using the Curl command. 

Using Postman 

Install Postman on your machine if it is not installed. 

Create a POST request. 

  • URL: http://localhost:4444/api/v1/sendmail 
  • Content Type: JSON – Body tab > select JSON from dropdown 

Request Body 

{ 
"from": "hello@schadokar.dev", 
"to": ["shubham@schadokar.dev"], 
"subject": "Mail from Nodemailer", 
"text": "Sending an email using nodemailer package." 
} 

Hit Send. Make sure the server is running. 

Learn Nodemailer Module in Node.js

On Success, the response returns the message id. Now, check your mailbox. 

If you are unable to find the mail in your Inbox, check the promotional mail folder. 

Learn Nodemailer Module in Node.js

Using Curl Command

Open the terminal or cmd.

In the below curl command, change the parameters and enter.

curl -X POST http://localhost:4444/api/v1/sendmail -H "Content-Type:application/json" -d '{"from": "hello@schadokar.dev","to": ["shubham@schadokar.dev"],"subject": "Mail from Nodemailer", "text": "Sending an email using nodemailer package."}'

Learn Nodemailer Module in Node.js

In this example, we have sent a simple text message to the recipient.  

Nodemailer also gives you an option to send the message in HTML format. 

Mail template 

Open the mail.html in the code editor and paste the below code. 

<div style="text-align: center;"">
 <h1 style="color: #3584c8;">Nodemailer Example</h1>
  <p>

   This is an example html template to demonstrate the sending email using html.   

<br />
Shubham

Shubham Chadokar

Author

I am a Software Engineer who loves to write articles and tutorials on the latest technologies. I write majorly on Nodejs and Golang. 

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1 comments

Elke 17 Nov 2020

I have been browsing online more than 4 hours today, yet I never found any interesting article like yours. it is pretty worth enough for me. Personally, if all web owners and bloggers made good content as you did, the web will be much more useful than ever before.

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The event handling in react is declarative and the advantage of declarative way to handlers is that they are part of the User interface structure.  Let’s take a look at event handling in class components                       Import React, { Component } from ‘...react’                         class TestApp extends Component {                              clickHandler() {                                  console.log(“clicked”)                                }                                render(){                                      return(                                                                                     Click me                                                                                 )                                 }                            }                       export default TestApp You cannot return false to prevent default behaviour in React. You must call preventDefault explicitly.  In HTML it looks like below:    Click Output: It will print “Clicked”  And in React, like this:  function clickHandle(e) {       e.preventDefault();       console.log(“Handled”);   }  Click  Output : console will print “Handled”  There are some  event handlers triggered by an event in the bubbling phase which is the same as with the normal DOM API; simply attach a handler to an eventual parent of an element and any events triggered on that element will bubble to the parent as long as it's not stopped via stopPropagation along the way   Click me  Below are some of the event handlers triggered in the bubbling phase:  MouseEvents           onClick           onDrag          onDoubleClick Keyboard Events                    onKeyDown                    onKeyPress                    onKeyUp Focus Events                  onFocus   onBlur To capture an event handler for the capture phase, append capture to the event name. For example, instead of using onClick, use onClickCapture to handle the click event.  Capture event example:                  Click me    Additional ExamplesExample1                       Import React from ‘...react’                         function clickAppHandler() {                                function clickHandler() {                                        console.log(‘clicked’)                                         }                                  return (                                                                                  Click                                                                          )                         }                       export default clickAppHandler   Example2       This example is along with HTML in a single file                                                            Events                               function testApp (){                        alert((“Hello Event”);                                                   test Clicked                  test double Clicked                     Adding Events: Below example is how you add an event. Highlighted in bold                      Import React from ‘...react’                         function clickAppHandler() {                                function clickHandler() {                                        console.log(‘clicked’)                                         }                                  return (                                                                                  Click                                                                          )                         }                       export default clickAppHandler  Passing Arguments to Event HandlerThere are two ways arguments are passed to event handler  Arrow function                    this.handleClick(id,e)}>Click                onClick is the event                e is the event object                 id can be state or props or some data Bind method      Click  In this case event object is automatically passed In both methods e represents the react event and its passed after the ID as second argument,With an arrow function this event e is passed explicitly but with bind method its automatically passed.                                     Import React,{ Component } from “react”;                                         class TestApp extends Component {                                           state = {                                                       id: 2,                                                      Name: “TestApp Dummy”                                                };                                                             //arrow function                                                 handleClick = (id,e) => {                                                       console.log(id);                                                       console.log(e);                                                  };                                               handleArg = (e) => { this.handleClick(this.state.id,e);}                                                          render() {     return (                    TestApp,{this.state.name}            onClick={this.handleArg}>Display            );   }  }  The react event is an object and obtained from react. Instead of creating a separate function for passing argument, you can directly pass the anonymous arrow function as shown in the render function below:     render() {        return (                                                                                                       TestApp,{this.state.name}                                                {                           this.handleClick(this.state.id,e);                                                               }}>Display                                                                                                         );                                                 }                                            }    Output:   click on button  “TestApp Dummy “                   Let’s see only how bind method looks like in the render function    render() {                                         return (                                                                                                 TestApp,{this.state.name}                                                   Display                                                                                                       );                                                  }                                              } Output: this will display the h1 tag and when you click the button handleClick function gets invoked and the console will display id of the state object as shown above. Building a Practice to Thoroughly Understand Events This blog focuses on event handling, which in turn teaches about event handlers declared in JSX markup.This approach helps in tracking down the element mapped with events in an easy way.  We also learned how to handle multiple event handlers in a single element by using JSX attributes.we also learned about ways to bind event handler and  parameter values. Then we learned about synthetic events which are abstractions around native events. The best way you can retain this learning is by practicing more and tackling the complexities that may arise as you practice. You can find several tutorials on the internet or share your questions with us here. Happy learning! 
5355
Handling React Events - A Detailed Guide

Event handling essentially allows the user to inte... Read More

MongoDB Query Document Using Find() With Example

MongoDB's find() method selects documents from a collection or view and returns a cursor to those documents. There are two parameters in this formula: query and projection.Query – This is an optional parameter that specifies the criteria for selection. In simple terms, a query is what you want to search for within a collection.Projection – This is an optional parameter that specifies what should be returned if the query criteria are satisfied. In simple terms, it is a type of decision-making that is based on a set of criteria.MongoDB's Flexible SchemaA NoSQL database, which stands for "not only SQL," is a way of storing and retrieving data that is different from relational databases' traditional table structures (RDBMS).When storing large amounts of unstructured data with changing schemas, NoSQL databases are indeed a better option than RDBMS. Horizontal scaling properties of NoSQL databases allow them to store and process large amounts of data.These are intended for storing, retrieving, and managing document-oriented data, which is frequently stored in JSON format (JavaScript Object Notation). Document databases, unlike RDBMSs, have a flexible schema that is defined by the contents of the documents.MongoDB is one of the most widely used open-source NoSQL document databases. MongoDB is known as a 'schemaless' database because it does not impose a specific structure on documents in a collection.MongoDB is compatible with a number of popular programming languages. It also offers a high level of operational flexibility because it scales well horizontally, allowing data to be spread or 'sharded' across multiple commodity servers with the ability to add more servers as needed. MongoDB can be run on a variety of platforms, including developer laptops, private clouds, and public clouds.Querying documents using find()MongoDB queries are used to retrieve or fetch data from a MongoDB database. When running a query, you can use criteria or conditions to retrieve specific data from the database.The function db.collection is provided by MongoDB. find() is a function that retrieves documents from a MongoDB database.In MongoDB, the find method is used to retrieve a specific document from the MongoDB collection. In Mongo DB, there are a total of six methods for retrieving specific records.find()findAndModify()findOne()findOneAndDelete()findOneAndReplace()findOneAndUpdate()Syntax:find(query, projection)We can fetch a specific record using the Find method, which has two parameters. If these two parameters are omitted, the find method will return all of the documents in the MongoDB collection.Example:Consider an example of employees with the database of employee_id and employee_name and we will fetch the documents using find() method.First, create a database with the name “employees” with the following code:use employeesNow, create a collection “employee” with:db.createCollection("employee")In the next step we will insert the documents in the database:db.employee.insert([{employee_id: 101, employee_name: "Ishan"}, {employee_id: 102, employee_name: "Bhavesh"}, {employee_id: 103, employee_name: "Madan"}])Find all Documents:To get all the records in a collection, we need to use the find method with an empty parameter. In other words, when we need all the records, we will not use any parameters.db.employee.find()Output in Mongo ShellThe pretty() method can be used to display the results in a formatted manner.Syntax:db.COLLECTION_NAME.find().pretty()Let’s check our documents with pretty() method:Query FiltersWe will see examples of query operations using the db.collection.find() method in mongosh.We will use the employee collection in the employees database.db.employee.insert([{employee_id: 101, employee_name: "Ishan", age: 21, email_id: "ishanjain@gmail.com"}, {employee_id: 102, employee_name: "Bhavesh", age: 22, email_id: "bhaveshg@gmail.com"}, {employee_id: 103, employee_name: "Madan", age: 23, email_id: "madan@gmail.com"}])As we have seen earlier that to select all the documents in the database we pass an empty document as the query filter parameter to the find method.db.employee.find().pretty()Find the first document in a collection:db.employee.findOne()Find a document by ID:db.employee.findOne({_id : ObjectId("61d1ae0b56b92c20b423a5a7")})Find Documents that Match Query Criteriadb.employee.find({“age”: “22”})db.employee.find({"employee_name": "Madan"}).pretty()Sort Results by a Field:db.employee.find().sort({age: 1}).pretty()order by age, in ascending orderdb.employee.find().sort({age: -1}).pretty()order by age, in descending orderAND Conditions:A compound query can specify conditions for multiple fields in the documents in a collection. A logical AND conjunction connects the clauses of a compound query indirectly, allowing the query to select all documents in the collection that meet the specified conditions.In the following example, we will consider all the documents in the employee collection where employee_id equals 101 and age equals 21.db.employee.find({"employee_id": 101, "age": "21" }).pretty()Querying nested fieldsThe embedded or nested document feature in MongoDB is a useful feature. Embedded documents, also known as nested documents, are documents that contain other documents.You can simply embed a document inside another document in MongoDB. Documents are defined in the mongo shell using curly braces (), and field-value pairs are contained within these curly braces.Using curly braces, we can now embed or set another document inside these fields, which can include field-value pairs or another sub-document.Syntax:{ field: { field1: value1, field2: value2 } }Example:We have a database “nested” and in this database we have collection “nesteddoc”.The following documents will insert into the nesteddoc collection.db.nesteddoc.insertMany([ { "_id" : 1, "dept" : "A", "item" : { "sku" : "101", "color" : "red" }, "sizes" : [ "S", "M" ] }, { "_id" : 2, "dept" : "A", "item" : { "sku" : "102", "color" : "blue" }, "sizes" : [ "M", "L" ] }, { "_id" : 3, "dept" : "B", "item" : { "sku" : "103", "color" : "blue" }, "sizes" : "S" }, { "_id" : 4, "dept" : "A", "item" : { "sku" : "104", "color" : "black" }, "sizes" : [ "S" ] } ])Place the documents in the collection now. Also, take a look at the results:As a result, the nesteddoc collection contains four documents, each of which contains nested documents. The find() method can be used to access the collection's documents.db.nesteddoc.find()Specify Equality Condition:In this example, we will select the document from the nesteddoc query where dept equals “A”.db.nesteddoc.find({dept: "A"})Querying ArraysUse the query document {: } to specify an equality condition on an array, where is the exact array to match, including the order of the elements.The following query looks for all documents where the field tags value is an array with exactly two elements, "S" and "M," in the order specified:db.nesteddoc.find( { sizes: ["S", "M"] } )Use the $all operator to find an array that contains both the elements "S" and "M," regardless of order or other elements in the array:db.nested.find( { sizes: { $all: ["S", "M"] } } )Query an Array for an Element:The following example queries for all documents where size is an array that contains the string “S” as one of its elements:db.nesteddoc.find( { sizes: "S" } )Filter conditionsTo discuss the filter conditions, we will consider a situation that elaborates this. We will start by creating a collection with the name “products” and then add the documents to it.db.products.insertMany([ { _id: 1, item: { name: "ab", code: "123" }, qty: 15, tags: [ "A", "B", "C" ] }, { _id: 2, item: { name: "cd", code: "123" }, qty: 20, tags: [ "B" ] }, { _id: 3, item: { name: "ij", code: "456" }, qty: 25, tags: [ "A", "B" ] }, { _id: 4, item: { name: "xy", code: "456" }, qty: 30, tags: [ "B", "A" ] }, { _id: 5, item: { name: "mn", code: "000" }, qty: 20, tags: [ [ "A", "B" ], "C" ] }])To check the documents, use db.products.find():$gt$gt selects documents with a field value greater than (or equal to) the specified value.db.products.find( { qty: { $gt: “20” } } )$gte:$gte finds documents in which a field's value is greater than or equal to (i.e. >=) a specified value (e.g. value.)db.products.find( { qty: { $gte: 20 } } )$lt:$lt selects documents whose field value is less than (or equal to) the specified value.db.products.find( { qty: { $lt: 25 } } )$lte:$lte selects documents in which the field's value is less than or equal to (i.e. =) the specified value.db.products.find( { qty: { $lte: 20 } } )Query an Array by Array Length:To find arrays with a specific number of elements, use the $size operator. For example, the following selects documents with two elements in the array.db.products.find( { "tags": {$size: 2} } )ProjectionIn MongoDB, projection refers to selecting only the data that is required rather than the entire document's data. If a document has five fields and you only want to show three of them, select only three of them.The find() method in MongoDB accepts a second optional parameter, which is a list of fields to retrieve, as explained in MongoDB Query Document. When you use the find() method in MongoDB, it displays all of a document's fields. To prevent this, create a list of fields with the values 1 or 0. The value 1 indicates that the field should be visible, while 0 indicates that it should be hidden.Syntax:db.COLLECTION_NAME.find({},{KEY:1})Example:We will consider the previous example of products collection. Run the below command on mongoshell to learn how projection works:db.products.find({},{"tags":1, _id:0})Keep in mind that the _id field is always displayed while executing the find() method; if you do not want this field to be displayed, set it to 0.Optimized FindingsTo retrieve a document from a MongoDB collection, use the Find method.Using the Find method, we can retrieve specific documents as well as the fields that we require. Other find methods can also be used to retrieve specific documents based on our needs.By inserting array elements into the query, we can retrieve specific elements or documents. To retrieve data for array elements from the collection in MongoDB, we can use multiple query operators.
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MongoDB Query Document Using Find() With Example

MongoDB's find() method selects documents from a c... Read More

Implementing MongoDb Map Reduce using Aggregation

Algorithms and applications in today's data-driven market collect data about people, processes, systems, and organisations 24 hours a day, seven days a week, resulting in massive amounts of data. The problem is figuring out how to process this massive amount of data efficiently without sacrificing valuable insights.What is Map Reduce? The MapReduce programming model comes to the rescue here. MapReduce, which was first used by Google to analyse its search results, has grown in popularity due to its ability to split and process terabytes of data in parallel, generating results faster. A (Key,value) pair is the basic unit of information in MapReduce. Before feeding the data to the MapReduce model, all types of structured and unstructured data must be translated to this basic unit. The MapReduce model, as the name implies, consists of two distinct routines: the Map-function and the Reduce-function.  MapReduce is a framework for handling parallelizable problems across huge files using a huge number of devices (nodes), which are collectively referred to as a cluster (if all nodes are on the same local network and use similar hardware) or a grid (if the nodes are shared across geographically and administratively distributed systems, and use more heterogeneous hardware).  When data stored in a filesystem (unstructured) or a database(structured) is processed, MapReduce can take advantage of data's locality, processing it close to where it's stored to reduce communication costs. Typically, a MapReduce framework (or system) consists of three operations: Map: Each worker node applies the map function to local data and saves the result to a temporary storage. Only one copy of the redundant input data is processed by a master node. Shuffle: worker nodes redistribute data based on output keys (produced by the map function), ensuring that all data associated with a single key is stored on the same worker node. Reduce: each group of output data is now processed in parallel by worker nodes, per key. This article will walk you through the Map-Reduce model's functionality step by step. Map Reduce in MongoDB The map-reduce operation has been deprecated since MongoDB 5.0. An aggregation pipeline outperforms a map-reduce operation in terms of performance and usability. Aggregation pipeline operators like $group, $merge, and others can be used to rewrite map-reduce operations. Starting with version 4.4, MongoDB provides the $accumulator and $function aggregation operators for map-reduce operations that require custom functionality. In JavaScript, use these operators to create custom aggregation expressions. The map and reduce functions are the two main functions here. As a result, the data is independently mapped and reduced in different spaces before being combined in the function and saved to the specified new collection. This mapReduce() function was designed to work with large data sets only. You can perform aggregation operations like max and avg on data using Map Reduce, which is similar to groupBy in SQL. It works independently and in parallel on data. Implementing Map Reduce with Mongosh (MongoDB Shell)  The db.collection.mapReduce() method in mongosh is a wrapper for the mapReduce command. The examples that follow make use of the db.collection.mapReduce(). Example: Create a collection ‘orders’ with these documents: db.orders.insertMany([     { _id: 1, cust_id: "Ishan Jain", ord_date: new Date("2021-11-01"), price: 25, items: [ { sku: "oranges", qty: 5, price: 2.5 }, { sku: "apples", qty: 5, price: 2.5 } ], status: "A" },     { _id: 2, cust_id: "Ishan Jain", ord_date: new Date("2021-11-08"), price: 70, items: [ { sku: "oranges", qty: 8, price: 2.5 }, { sku: "chocolates", qty: 5, price: 10 } ], status: "A" },     { _id: 3, cust_id: "Bhavesh Galav", ord_date: new Date("2021-11-08"), price: 50, items: [ { sku: "oranges", qty: 10, price: 2.5 }, { sku: "pears", qty: 10, price: 2.5 } ], status: "A" },     { _id: 4, cust_id: "Bhavesh Galav", ord_date: new Date("2021-11-18"), price: 25, items: [ { sku: "oranges", qty: 10, price: 2.5 } ], status: "A" },     { _id: 5, cust_id: "Bhavesh Galav", ord_date: new Date("2021-11-19"), price: 50, items: [ { sku: "chocolates", qty: 5, price: 10 } ], status: "A"},     { _id: 6, cust_id: "Madan Parmar", ord_date: new Date("2021-11-19"), price: 35, items: [ { sku: "carrots", qty: 10, price: 1.0 }, { sku: "apples", qty: 10, price: 2.5 } ], status: "A" },     { _id: 7, cust_id: "Madan Parmar", ord_date: new Date("2021-11-20"), price: 25, items: [ { sku: "oranges", qty: 10, price: 2.5 } ], status: "A" },     { _id: 8, cust_id: "Abhresh", ord_date: new Date("2021-11-20"), price: 75, items: [ { sku: "chocolates", qty: 5, price: 10 }, { sku: "apples", qty: 10, price: 2.5 } ], status: "A" },     { _id: 9, cust_id: "Abhresh", ord_date: new Date("2021-11-20"), price: 55, items: [ { sku: "carrots", qty: 5, price: 1.0 }, { sku: "apples", qty: 10, price: 2.5 }, { sku: "oranges", qty: 10, price: 2.5 } ], status: "A" },     { _id: 10, cust_id: "Abhresh", ord_date: new Date("2021-11-23"), price: 25, items: [ { sku: "oranges", qty: 10, price: 2.5 } ], status: "A" }  ]) Apply a map-reduce operation to the orders collection to group them by cust_id, then add the prices for each cust_id: To process each input document, define the map function: this refers the document that the map-reduce operation is processing in the function. For each document, the function maps the price to the cust_id and outputs the cust_id and price. var mapFunction1 = function() {emit(this.cust_id, this.price);}; With the two arguments keyCustId and valuesPrices, define the corresponding reduce function: The elements of the valuesPrices array are the price values emitted by the map function, grouped by keyCustId. The valuesPrice array is reduced to the sum of its elements by this function. var reduceFunction1 = function(keyCustId, valuesPrices) {return Array.sum(valuesPrices);};Apply the mapFunction1 map function and the reduceFunction1 reduce function to all documents in the orders collection: db.orders.mapReduce(mapFunction1,reduceFunction1,{ out: "map_reduce_example" }) The results of this operation are saved in the map_reduce_example collection. If the map_reduce_example collection already exists, the operation will overwrite its contents with the map-reduce operation's results. Check the map_reduce_example collection to verify: db.map_reduce_example.find().sort( { _id: 1 } ) Aggregation Alternative:You can rewrite the map-reduce operation without defining custom functions by using the available aggregation pipeline operators: db.orders.aggregate([{$group: { _id:"$cust_id",value:{$sum: "$price" } } },{ $out: "agg_alternative_1" }]) Check the agg_alternative_1 collection to verify: db.agg_alternative_1.find().sort( { _id: 1 } )Implementing Map Reduce with Java Consider the collection car and insert the following documents in it. db.car.insert( [ {car_id:"c1",name:"Audi",color:"Black",cno:"H110",mfdcountry:"Germany",speed:72,price:11.25}, {car_id:"c2",name:"Polo",color:"White",cno:"H111",mfdcountry:"Japan",speed:65,price:8.5}, {car_id:"c3",name:"Alto",color:"Silver",cno:"H112",mfdcountry:"India",speed:53,price:4.5}, {car_id:"c4",name:"Santro",color:"Grey",cno:"H113",mfdcountry:"Sweden",speed:89,price:3.5} , {car_id:"c5",name:"Zen",color:"Blue",cno:"H114",mfdcountry:"Denmark",speed:94,price:6.5} ] ) You will get an output like this:  Let's now write the map reduce function on a collection of cars, grouping them by speed and classifying them as overspeed cars.  var speedmap = function (){  var criteria;  if ( this.speed > 70 ) {criteria = 'overspeed';emit(criteria,this.speed);}}; Based on the speed, this function classifies the vehicle as an overspeed vehicle. The term "this" refers to the current document that requires map reduction. var avgspeed_reducemap = function(key, speed) {       var total =0;       for (var i = 0; i 
7344
Implementing MongoDb Map Reduce using Aggregation

Algorithms and applications in today's data-driven... Read More