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How to Install Node.JS on a Mac

Node.js is an opensource JavaScript platform for general-purpose programming that allows users to quickly build network applications. As it uses JavaScript on both the front and backend, development becomes far more consistent and integrated. Node.js runs on various platforms (Windows, Linux, Unix, Mac OS, etc.) In this tutorial, we will discuss about Node.js installation on macOS.As we have already mentioned, Node.js allows you to write JavaScript on the server-side. JavaScript, as you know, is a browser-based language. The creator of Node.js took the engine of Chrome and set it to work on a server. The browser's engine compiles JavaScript code into commands, and the language can be interpreted in an environment.  Npm is the platform for Node.js package management. It offers a tool for Node.js libraries to be installed, and their versions and dependencies managed.PrerequisitesHardware Requirement:RAM: 4 GB Storage: 256 GB of Hard Disk Space Software Requirements:Web Browser: Any browser such as Google Chrome, Mozilla Firefox, Microsoft Edge, Safari.XCode: XCode software is used by Apple in building Mac and iOS applications, so it provides the instruments you need to compile Mac software. You can find XCode in the Apple App Store.  Homebrew: Homebrew is a package manager for the Mac. It readily allows the installation of most open-source software (like Node).  On the Homebrew website, you can find out more about Homebrew.Operating System: macOSInstallation ProcedureIn this article, we are going to look at three different ways to install Node.js on macOS.using the macOS installer  using homebrew  using Node Version ManagerSo, let us start.1. Using the macOS installerStep 1: Visit the Node.js website to update your Mac platform with the built installer.Node.js updates comprise two types, long-term support (LTS) and new releases. LTS versions are refined and bug-free, and are sufficient for most daily users. Current versions (Latest LTS 14.16.1) are more experimental and include the new functionality, which cannot be completed or crashed from time to time. By highlighting the field on the first tab, you can move between LTS and current versions. Again, most users use the LTS version. Therefore, you can just click on macOS installer, which will download the Node.js installer, if the LTS tab is highlighted in dark green.Step 2: Download .pkg installer and open the downloaded file with default installer.Step 3: After running the .pkg installer, follow the instructions on the interface.1. Introduction window: select Continue2. Licence window: Select Continue and a pop-up window will ask you to agree or disagree. Click on Agree to proceed.3. Select Install and Authenticate your macOS password.4. You will see that Node.js and npm are installed on the interface.Step 4: Verify the installation of Node.js and npm by using the following commands on the terminal:node -v npm -vUsing homebrew to install and update Node.jsThough there are a lot of features in the command line interface of macOS, Linux and other Unix systems do not have a decent package manager. A Package Manager consists of a series of software tools that automatically install, configure and update the software.They manage the software in a central location and maintain all the device software packages in widely used formats. The Homebrew software package management framework is free and open-source and simplifies the installation of macOS software. The latest version of Node.js can be installed using Homebrew.Step 1: Use the following command to install Homebrew:s$ /usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"When CURL downloads the script, the Ruby-interpreter starts the Homebrew installation process, which ships with macOS.During the operation, you will be asked to enter your password. While you don't see them, the machine records your keystrokes, so once your password has been entered, click the RETURN key.Step 2: Once homebrew is installed, use the following command to install Node.js:$ brew update $ brew install nodeStep 3: Verify the installation and check the version of Node.js and npm.$ node -v $ npm -vHomebrew always installs only the latest version of Node.js. This may be problematic since a certain version of Node.js might be required to function in applications. It can be a good thing to have the freedom to use those versions. The easiest way to solve this problem is by using NVM, the Node Version Manager.Using nvm to install and update Node.jsNVM is a bash script for several active versions of Node.js. Follow these steps to install Node.js:Step 1: The script copies the nvm-repository to ~/.nvm and then attaches the sources to the profile of the shell: ~/.bash profile, ~/.zshrc and ~/.profile or ~/.bashrc. Depending on what you have on your machine you can use curlUse the following command:$ curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.35.3/install.sh | bashStep 2:  Add the source lines in your shell profile. You can use ~/.bash_profile, ~/.zshrc, ~/.profile, or ~/.bashrc. In this article, we will be using zsh shell:$ vim .zshrcStep 3: Paste the following lines of code:export NVM_DIR="$HOME/.nvm"[ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh" [ -s "$NVM_DIR/bash_completion" ] && \. "\$NVM_DIR/bash_completion"Close the file by using esc + w + qStep 4: Use the following command to reload the shell:$ source ~/.zshrcStep 5: You can verify the installation with the following command and if the screen shown had nvm written as the output, then the installation is successful.$ command -v nvmNote: You can check the various commands of nvm with the following command:$ nvm + tab keyStep 6: Install LTS version:$ nvm install –ltsStep 7: Install the latest version of node:$ nvm install nodeThis is an alias for the latest version.Step 8: You can list out all the installed Node.js versions available on your system:$ nvm listStep 9: Install NPM:$ nvm install-latest -npmStep 10: This installs the latest NPM. After you've set up NPM, you can try out a number of useful commands:List and update globally installed packages:$ npm ls -g  --depth=0 $ npm update  -gCreate a simple ProgramLet's create a simple program "Hello, world." This ensures that our environment works and that you can build and run a Node.js program conveniently.Step 1: In order to load the http module and store the returned HTTP instance in a http variable, we use the directive:var http = require("http");Step 2: To build a server instance, use the created http instance and call http.createServer() and connect it to port 8081 through the servers instance. Pass a function with request and response parameters. We will print Hello World!http.createServer(function (request, response) {    // Send the HTTP header      // HTTP Status: 200 : OK    // Content Type: text/plain    response.writeHead(200, {'Content-Type': 'text/plain'});    response.end('Hello World\n'); }).listen(8081); console.log('Server running at http://127.0.0.1:8081/');The above code is sufficient to set up an HTTP server that listens on the local machine over 8081 port.Step 3: Create a hello.js file using the following command:$ nano hello.jsStep 4: We will combine both the steps in a file hello.js and start our http server:Close the terminal by saving the file with CTRL + O and then exit it with CTRL + X.Step 5: Execute the hello.js to start the server with the following command:$ node hello.jsStep 6: Check the server at http://127.0.0.1:8081/Finally, we have our first http server up.Uninstall Node.js on macOSEarlier we have discussed the installation of Node.js on Mac with three different methods. Now, we will discuss the different ways to uninstall Node.js from your system:1. ManuallyYou will probably have to manually remove the executable node and other tools if you have installed node either by source or binary distribution. This is not simple, unfortunately, because several folders, such as npm and node modules, contain node resources.Use this official command to delete the node, node_modules folder:$ curl -ksO   https://gist.githubusercontent.com/nicerobot/2697848/raw/uninstall-node.sh $ chmod +x ./uninstall-node.sh $ ./uninstall-node.sh $ rm uninstall-node.sh2. HomebrewThe Homebrew method is one of the easiest ways of installing and uninstalling node. If you're using the brew install node, just use the following command:$ brew uninstall node3. Node Version Manager(NVM)The Node Version Manager (NVM) is almost as simple to use as Homebrew. You can install several node versions on your system to allow you to migrate easily from one version to the next.Finally, when you're done, you'll probably want to get rid of one of the versions. You can do this quickly:$ nvm uninstall <version>For example:$ nvm uninstall v16.0.0.1ConclusionYou have installed Node.js, npm successfully and checked the setup using a simple program. You can now use it to build applications on the client or on the server.You have also seen how to install Node.js via homebrew, probably the most popular macOS package manager.However, Node Version Manager is the fastest way to install Node.js. This provides additional control and versatility in adopting various versions of Node.js, which may be needed if you switch between different projects based on your needs.

How to Install Node.JS on a Mac

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How to Install Node.JS on a Mac

Node.js is an opensource JavaScript platform for general-purpose programming that allows users to quickly build network applications. As it uses JavaScript on both the front and backend, development becomes far more consistent and integrated. 

Node.js runs on various platforms (Windows, Linux, Unix, Mac OS, etc.) In this tutorial, we will discuss about Node.js installation on macOS.

As we have already mentioned, Node.js allows you to write JavaScript on the server-side.  JavaScript, as you know, is a browser-based language. The creator of Node.js took the engine of Chrome and set it to work on a server. The browser's engine compiles JavaScript code into commands, and the language can be interpreted in an environment.   

Npm is the platform for Node.js package management. It offers a tool for Node.js libraries to be installed, and their versions and dependencies managed.

Prerequisites

Hardware Requirement:

  • RAM: 4 GB 
  • Storage: 256 GB of Hard Disk Space

  Software Requirements:

  • Web Browser: Any browser such as Google Chrome, Mozilla Firefox, Microsoft Edge, Safari.
  • XCode: XCode software is used by Apple in building Mac and iOS applications, so it provides the instruments you need to compile Mac software. You can find XCode in the Apple App Store.  
  • Homebrew: Homebrew is a package manager for the Mac. It readily allows the installation of most open-source software (like Node).  On the Homebrew website, you can find out more about Homebrew.
  • Operating System: macOS

Installation Procedure

In this article, we are going to look at three different ways to install Node.js on macOS.

  1. using the macOS installer  
  2. using homebrew  
  3. using Node Version Manager

So, let us start.

1. Using the macOS installer

Step 1: Visit the Node.js website to update your Mac platform with the built installer.

Node.js updates comprise two types, long-term support (LTS) and new releases. LTS versions are refined and bug-free, and are sufficient for most daily users. Current versions (Latest LTS 14.16.1) are more experimental and include the new functionality, which cannot be completed or crashed from time to time. By highlighting the field on the first tab, you can move between LTS and current versions. Again, most users use the LTS version. Therefore, you can just click on macOS installer, which will download the Node.js installer, if the LTS tab is highlighted in dark green.

Step 2: Download .pkg installer and open the downloaded file with default installer.

Step 3: After running the .pkg installer, follow the instructions on the interface.

1. Introduction window: select Continue

2. Licence window: Select Continue and a pop-up window will ask you to agree or disagree. Click on Agree to proceed.

3. Select Install and Authenticate your macOS password.

4. You will see that Node.js and npm are installed on the interface.

Step 4: Verify the installation of Node.js and npm by using the following commands on the terminal:

node -v
npm -v

Using homebrew to install and update Node.js

Though there are a lot of features in the command line interface of macOS, Linux and other Unix systems do not have a decent package manager. A Package Manager consists of a series of software tools that automatically install, configure and update the software.

They manage the software in a central location and maintain all the device software packages in widely used formats. The Homebrew software package management framework is free and open-source and simplifies the installation of macOS software. The latest version of Node.js can be installed using Homebrew.

Step 1: Use the following command to install Homebrew:

s$ /usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

When CURL downloads the script, the Ruby-interpreter starts the Homebrew installation process, which ships with macOS.

During the operation, you will be asked to enter your password. While you don't see them, the machine records your keystrokes, so once your password has been entered, click the RETURN key.

Step 2: Once homebrew is installed, use the following command to install Node.js:

$ brew update
$ brew install node

Step 3: Verify the installation and check the version of Node.js and npm.

$ node -v
$ npm -v

Homebrew always installs only the latest version of Node.js. This may be problematic since a certain version of Node.js might be required to function in applications. It can be a good thing to have the freedom to use those versions. The easiest way to solve this problem is by using NVM, the Node Version Manager.

Using nvm to install and update Node.js

NVM is a bash script for several active versions of Node.js. Follow these steps to install Node.js:

Step 1: The script copies the nvm-repository to ~/.nvm and then attaches the sources to the profile of the shell: ~/.bash profile, ~/.zshrc and ~/.profile or ~/.bashrc. Depending on what you have on your machine you can use curl

Use the following command:

$ curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.35.3/install.sh | bash

Step 2:  Add the source lines in your shell profile. You can use ~/.bash_profile, ~/.zshrc, ~/.profile, or ~/.bashrc. In this article, we will be using zsh shell:

$ vim .zshrc

Step 3: Paste the following lines of code:

export NVM_DIR="$HOME/.nvm"[ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh" [ -s "$NVM_DIR/bash_completion" ] && \. "\$NVM_DIR/bash_completion"

Close the file by using esc + w + q

Step 4: Use the following command to reload the shell:

$ source ~/.zshrc

Step 5: You can verify the installation with the following command and if the screen shown had nvm written as the output, then the installation is successful.

$ command -v nvm

Note: You can check the various commands of nvm with the following command:

$ nvm + tab key

Step 6: Install LTS version:

$ nvm install –lts

Step 7: Install the latest version of node:

$ nvm install node

This is an alias for the latest version.

Step 8: You can list out all the installed Node.js versions available on your system:

$ nvm list

Step 9: Install NPM:

$ nvm install-latest -npm

Step 10: This installs the latest NPM. After you've set up NPM, you can try out a number of useful commands:

List and update globally installed packages:

$ npm ls -g  --depth=0
$ npm update  -g

Create a simple Program

Let's create a simple program "Hello, world." This ensures that our environment works and that you can build and run a Node.js program conveniently.

Step 1: In order to load the http module and store the returned HTTP instance in a http variable, we use the directive:

var http = require("http");

Step 2: To build a server instance, use the created http instance and call http.createServer() and connect it to port 8081 through the servers instance. Pass a function with request and response parameters. We will print Hello World!

http.createServer(function (request, response) {
   // Send the HTTP header  
   // HTTP Status: 200 : OK
   // Content Type: text/plain
   response.writeHead(200, {'Content-Type': 'text/plain'});
   response.end('Hello World\n');
}).listen(8081);
console.log('Server running at http://127.0.0.1:8081/');

The above code is sufficient to set up an HTTP server that listens on the local machine over 8081 port.

Step 3: Create a hello.js file using the following command:

$ nano hello.js

Step 4: We will combine both the steps in a file hello.js and start our http server:

Close the terminal by saving the file with CTRL + O and then exit it with CTRL + X.

Step 5: Execute the hello.js to start the server with the following command:

$ node hello.js

Step 6: Check the server at http://127.0.0.1:8081/

Finally, we have our first http server up.

Uninstall Node.js on macOS

Earlier we have discussed the installation of Node.js on Mac with three different methods. Now, we will discuss the different ways to uninstall Node.js from your system:

1. Manually

You will probably have to manually remove the executable node and other tools if you have installed node either by source or binary distribution. This is not simple, unfortunately, because several folders, such as npm and node modules, contain node resources.

Use this official command to delete the node, node_modules folder:

$ curl -ksO  
https://gist.githubusercontent.com/nicerobot/2697848/raw/uninstall-node.sh
$ chmod +x ./uninstall-node.sh
$ ./uninstall-node.sh
$ rm uninstall-node.sh

2. Homebrew

The Homebrew method is one of the easiest ways of installing and uninstalling node. If you're using the brew install node, just use the following command:

$ brew uninstall node

3. Node Version Manager(NVM)

The Node Version Manager (NVM) is almost as simple to use as Homebrew. You can install several node versions on your system to allow you to migrate easily from one version to the next.

Finally, when you're done, you'll probably want to get rid of one of the versions. You can do this quickly:

$ nvm uninstall <version>

For example:

$ nvm uninstall v16.0.0.1

Conclusion

You have installed Node.js, npm successfully and checked the setup using a simple program. You can now use it to build applications on the client or on the server.

You have also seen how to install Node.js via homebrew, probably the most popular macOS package manager.

However, Node Version Manager is the fastest way to install Node.js. This provides additional control and versatility in adopting various versions of Node.js, which may be needed if you switch between different projects based on your needs.

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Website : https://www.knowledgehut.com

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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