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Install And Setup React App on Ubuntu

React is a JavaScript library for building user interfaces. It is opensource and maintained by Facebook.You can read more about React here.In this blog we are going to learn how to install and setup a React App on Ubuntu (version 16 and above).PrerequisitesThis blog assumes that you are using Ubuntu 16 or above versions and you have all the privileges to install the software in the machine, and also have access to the required websites mentioned in the blog.System Requirements:Ubuntu 16 or aboveMinimum 4GB RAMVisual Studio Code installed.Why should we choose React, and what are its advantages?React is built on JavaScript which makes it easier to learn and easier to use.React is component based which means we can write re-usable components. Start with small things, which you use to build bigger things, which you use to build apps.React is lightweight compared to Angular; which in turn makes your application faster to load—which is very important from the user’s point of view.React ensures faster rendering of DOM (document object model), this has been achieved by the introduction of Virtual DOM-currently, one of the benefits of using React for heavy loaded and dynamic software solutions.React has a helpful and interactive developer toolset which makes it easy to debug. React Developer Tools is a browser extension available for both Chrome and Firefox. It enables developers to observe reactive component hierarchies, discover child and parent components, and inspect their current state and props.  React uses JSX(JavaScript XML) which has HTML-like syntax, making it easy to code and understand.React has strong community support on Github, Stackoverflow and many other platforms.React is SEO friendly.There are certainly many other nice features about using React.What is Node.js?Node.js is a JavaScript runtime built on Chrome's V8 JavaScript engine. Node.js is an Open Source Server Environment that is free and runs on almost all Operating Systems (Windows, Linux, Unix, Mac OS X, etc.).You can read more about Nodejs here.Why do we need Nodejs for React apps?Node.js lets developers use JavaScript to develop variety of applications like network applications, command line tools, web APIs, mobile applications, web applications etc.React usually runs on Node Server in development, but we can make use of other Servers likes Apache or Nginix to run React App in production. You do not need NodeJS to run React in production.What is NPM, why do we need NPM for React apps?NPM (Node Package Manager) is a dependency management tool for JavaScript applications. It is Open Source and also has command line utility for interacting with the application that aids in package installation, version management, and dependency management.React does not ship with all the features by itself, so it uses external packages to add the required features to the React application. These packages are maintained by NPM (Node package manager) which is shipped with Nodejs in development.You can read more about npm here.We can use yarn instead of NPM during development and production for React apps.Install Node.jsThere are many ways to install Node.js in an Ubuntu machine.Install Node.js from the Ubuntu repositoryInstall Using a PPA (personal package archive)Using the first method we will not get the latest version of Node.js installed so we will choose the second method where we will get the latest version of Node.js installed.Installing Using a PPA (personal package archive)To get the latest version of Node.js installed on ubuntu, add a PPA (personal package archive). It is maintained by NodeSource.Open terminal and run below commands:Install curl: Run below command on terminalCommand: sudo apt-get install curlSet the NodeSource PPA: Run below command on terminalCommand: curl -sL https://deb.nodesource.com/setup_current.x | sudo -E bash –The PPA will be added to your configuration and your local package cache will be updated automatically.You can read more about available versions of Node.js in nodesource here.Install Node.js: Run the below command on terminalCommand: sudo apt-get install -y nodejsCheck for Node.js Installation: Run below command on terminalCommand: node -vIt has to show the version of node installed in this case v15.4.0Now let's see how we can install and setup React app in Ubuntu machineUsing create-react-app (installing create-react-app using npm)Using npx (Recommended in React docs)Using create-react-app (npm)In setting up a React project we come across tools like babel and webpack which are not easy to understand and configure for a person who is new to React and JavaScript. There are several tools that help to sort this problem. One of them is create-react-app. This is the easiest to setup. Create-react-app comes with production grade configurations pre-built. You can alter the configurations by ejecting from the create-react-app as well.Follow the below steps to install using npm create-react-appGo into your desired location where you want to start your react app using ‘cd’ command Run below command to install create-react-app using npm Command: npm install -g create-react-appNow Run create-react-app on terminal to setup a React-app. Command: create-react-app hello-worldThis creates a folder with the name hello-world. You can navigate into the folder using ‘cd’ command and look at the project structure.This gives the React app which we can use, but React recommends using npx.Using npx command:npx is the package runner, since npm version 5.2.0 npx is pre-bundled with npm.Read more about differences npx and npm here.Follow the below steps to setup using npx.Go into your desired location where you want to start your react app using ‘cd’ commandRun the below command to setup React app using npxCommand: npx create-react-app my-appThat’s it! Your React app is ready with a single command.This creates a folder with the name hello-world. You can navigate into the folder using ‘cd’ command.  Now open the project in vs-codeWhen you open the project in visual studio code the structure looks like this.Now let's have a look at the files and folders we have:node_modules: This folder is managed by package manager (npm) and contains all the project library dependencies. We should not edit any file inside this folder.public: This folder contains the assets that should be served publicly without any restrictions and contains files like index.html, favicon, manifest.jsonsrc:  This is the folder that contains all the files that are used to create web applications. As a react developer you are likely to spend a lot of time in this folder creating components and other sources of code..gitignore: This file has all the assets which should be ignored by git while we publish our code to GitHub eg: node_modulespackage.json: This is a JSON file which has all information about the app such as name, dependencies, scripts we use to run the application etc.Readme.md: This is a markdown file where you specify the things which you want to show when someone visits your project on GitHub.Now let's run our first React app!Open the terminal integrated with Visual studio code or just stay in the ubuntu terminal; either is fine. Let's use the integrated terminal.Run the app using the following command: Command: npm startThis opens the app in your favourite browser as shown below:Now, let's make our first code changes:On navigating to src folder, you will find App.js file, through which the whole app is run inside the browser. Change the code as you see below and save by hitting ctrl+s.Now look at the browser where the app is running. It looks like the one in the image below.Congratulations on making your first React app!What you have learnt:What is React and why it should be usedWhat is Node.js, and how it should be installed on Ubuntu.What is npmWhat is create-react-appHow to setup React-app on UbuntuHow to run the React-app  How to make code changes to create your first React application.React has rapid changes for every new version. It is important to keep yourself updated with the latest releases of React, so that you can make your life as a React developer easier!

Install And Setup React App on Ubuntu

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Install And Setup React App on Ubuntu

React is a JavaScript library for building user interfaces. It is opensource and maintained by Facebook.

You can read more about React here.

In this blog we are going to learn how to install and setup a React App on Ubuntu (version 16 and above).

Prerequisites

This blog assumes that you are using Ubuntu 16 or above versions and you have all the privileges to install the software in the machine, and also have access to the required websites mentioned in the blog.

System Requirements:

  • Ubuntu 16 or above
  • Minimum 4GB RAM
  • Visual Studio Code installed.

Why should we choose React, and what are its advantages?

  • React is built on JavaScript which makes it easier to learn and easier to use.
  • React is component based which means we can write re-usable components. Start with small things, which you use to build bigger things, which you use to build apps.
  • React is lightweight compared to Angular; which in turn makes your application faster to load—which is very important from the user’s point of view.
  • React ensures faster rendering of DOM (document object model), this has been achieved by the introduction of Virtual DOM-currently, one of the benefits of using React for heavy loaded and dynamic software solutions.
  • React has a helpful and interactive developer toolset which makes it easy to debug. React Developer Tools is a browser extension available for both Chrome and Firefox. It enables developers to observe reactive component hierarchies, discover child and parent components, and inspect their current state and props.  
  • React uses JSX(JavaScript XML) which has HTML-like syntax, making it easy to code and understand.
  • React has strong community support on Github, Stackoverflow and many other platforms.
  • React is SEO friendly.

There are certainly many other nice features about using React.

What is Node.js?

Node.js is a JavaScript runtime built on Chrome's V8 JavaScript engine. Node.js is an Open Source Server Environment that is free and runs on almost all Operating Systems (Windows, Linux, Unix, Mac OS X, etc.).

You can read more about Nodejs here.

Why do we need Nodejs for React apps?

Node.js lets developers use JavaScript to develop variety of applications like network applications, command line tools, web APIs, mobile applications, web applications etc.

React usually runs on Node Server in development, but we can make use of other Servers likes Apache or Nginix to run React App in production. You do not need NodeJS to run React in production.

What is NPM, why do we need NPM for React apps?

NPM (Node Package Manager) is a dependency management tool for JavaScript applications. It is Open Source and also has command line utility for interacting with the application that aids in package installation, version management, and dependency management.

React does not ship with all the features by itself, so it uses external packages to add the required features to the React application. These packages are maintained by NPM (Node package manager) which is shipped with Nodejs in development.

You can read more about npm here.

We can use yarn instead of NPM during development and production for React apps.

Install Node.js

There are many ways to install Node.js in an Ubuntu machine.

  1. Install Node.js from the Ubuntu repository
  2. Install Using a PPA (personal package archive)

Using the first method we will not get the latest version of Node.js installed so we will choose the second method where we will get the latest version of Node.js installed.

Installing Using a PPA (personal package archive)

To get the latest version of Node.js installed on ubuntu, add a PPA (personal package archive). It is maintained by NodeSource.

Open terminal and run below commands:

  • Install curl: Run below command on terminal
    Command: sudo apt-get install curl

Install And Setup React App on Ubuntu

  • Set the NodeSource PPA: Run below command on terminal
    Command: curl -sL https://deb.nodesource.com/setup_current.x | sudo -E bash –

Install And Setup React App on Ubuntu

The PPA will be added to your configuration and your local package cache will be updated automatically.

You can read more about available versions of Node.js in nodesource here.

  • Install Node.js: Run the below command on terminal
    Command: sudo apt-get install -y nodejs

  • Check for Node.js Installation: Run below command on terminal
    Command: node -v
    It has to show the version of node installed in this case v15.4.0

Install And Setup React App on Ubuntu

Now let's see how we can install and setup React app in Ubuntu machine

  • Using create-react-app (installing create-react-app using npm)
  • Using npx (Recommended in React docs)

Using create-react-app (npm)

In setting up a React project we come across tools like babel and webpack which are not easy to understand and configure for a person who is new to React and JavaScript. There are several tools that help to sort this problem. One of them is create-react-app. This is the easiest to setup. Create-react-app comes with production grade configurations pre-built. You can alter the configurations by ejecting from the create-react-app as well.

Follow the below steps to install using npm create-react-app

  • Go into your desired location where you want to start your react app using ‘cd’ command 
  • Run below command to install create-react-app using npm 
    Command: npm install -g create-react-app

Install And Setup React App on Ubuntu

  • Now Run create-react-app on terminal to setup a React-app. 
    Command: create-react-app hello-world

Install And Setup React App on Ubuntu

  • This creates a folder with the name hello-world. You can navigate into the folder using ‘cd’ command and look at the project structure.

This gives the React app which we can use, but React recommends using npx.

Using npx command:

npx is the package runner, since npm version 5.2.0 npx is pre-bundled with npm.

Read more about differences npx and npm here.

Follow the below steps to setup using npx.

  • Go into your desired location where you want to start your react app using ‘cd’ command
  • Run the below command to setup React app using npx
    Command: npx create-react-app my-app
    That’s it! Your React app is ready with a single command.

Install And Setup React App on Ubuntu

  • This creates a folder with the name hello-world. You can navigate into the folder using ‘cd’ command.  
  • Now open the project in vs-code

When you open the project in visual studio code the structure looks like this.

Install And Setup React App on Ubuntu

Now let's have a look at the files and folders we have:

  • node_modules: This folder is managed by package manager (npm) and contains all the project library dependencies. We should not edit any file inside this folder.
  • public: This folder contains the assets that should be served publicly without any restrictions and contains files like index.html, favicon, manifest.json
  • src:  This is the folder that contains all the files that are used to create web applications. As a react developer you are likely to spend a lot of time in this folder creating components and other sources of code.
  • .gitignore: This file has all the assets which should be ignored by git while we publish our code to GitHub eg: node_modules
  • package.json: This is a JSON file which has all information about the app such as name, dependencies, scripts we use to run the application etc.
  • Readme.md: This is a markdown file where you specify the things which you want to show when someone visits your project on GitHub.

Now let's run our first React app!

  • Open the terminal integrated with Visual studio code or just stay in the ubuntu terminal; either is fine. Let's use the integrated terminal.
  • Run the app using the following command: 
    Command: npm start

Install And Setup React App on Ubuntu

This opens the app in your favourite browser as shown below:Install And Setup React App on Ubuntu

Now, let's make our first code changes:

On navigating to src folder, you will find App.js file, through which the whole app is run inside the browser. Change the code as you see below and save by hitting ctrl+s.

Install And Setup React App on Ubuntu

Now look at the browser where the app is running. It looks like the one in the image below.

Install And Setup React App on Ubuntu

Congratulations on making your first React app!

What you have learnt:

  • What is React and why it should be used
  • What is Node.js, and how it should be installed on Ubuntu.
  • What is npm
  • What is create-react-app
  • How to setup React-app on Ubuntu
  • How to run the React-app  
  • How to make code changes to create your first React application.

React has rapid changes for every new version. It is important to keep yourself updated with the latest releases of React, so that you can make your life as a React developer easier!

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Website : https://www.knowledgehut.com

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Handling React Events - A Detailed Guide

Event handling essentially allows the user to interact with a webpage and do something specific when a certain event like a click or a hover happens. When the user interacts with the application, events are fired, for example, mouseover, key press, change event, and so on. The application must handle events and execute the code. In short, events are the actions to which javascript can respond.   The actions to which javascript can respond are called events. Handling events with react is  very similar to handling events in DOM elements. Below are some general events that you would see in and out when dealing with react based websites:  Clicking an element  Submitting a form Scrolling page Hovering an element  Loading a webpage Input field change User stroking a key Image loading Naming Events in React Handling events with react is very similar to handling events in DOM elements, although there are some syntactic differences.   React events are written in camelCase.   A function is passed as the event handler rather than string. The way to write events in html / DOM is below:        click me onclick is written in lower case in html as shown above and what action to take when this onclick event triggers is taken care of by handleClick.In React, events are named using camel case and you pass a function as event handler as shown below:  Like in a functional component, event is written like below:       click me   In class based component ,event is written like below        click me Defining Events:Events are normally used in combination with functions, and the function is not executed until the event occurs, and the combination of event, HTML element, and javascript function is called binding which means to map all three. Generic syntax is:      Example:  Create a button element and what happens when onClick event triggered is driven by the function which is func() shown below     click me Let’s see some of the event attributes:   onmouseover : The mouse is moved over an element onmouseup : The mouse button is released onmouseout : The mouse  is moved off an element onmousemove: The mouse is moved Onmousedown: mouse button is pressed  onload : A image is done loading onunload: Existing the page  onblur : Losing Focus  on element  onchange : Content of a field changes onclick: Clicking an object  ondblclick: double clicking an object  onfocus element getting a focus  Onkeydown: pushing a keyboard key Onkeyup: keyboard key is released Onkeypress: keyboard key is pressed  Onselect: text is selected These are some examples of events:                                         Events                               function testApp (){                        alert((“Hello Event”);                                                   test Clicked                  test double Clicked                     Synthetic Events When you specify an event in JSX, you are not directly dealing with regular DOM events, you are dealing with a react event type called a synthetic event.It's a simple wrapper for native event instances and every synthetic event created needs to be garbage-collected which can be resource intensive in terms of CPU. The synthetic event object has properties mentioned below:  Boolean isTrusted  DOMEvent nativeEvent number timeStamp   void preventDefault() number eventPhase Synthetic events provide an interface and reduce browser inconsistencies and the event contains required information for its propagation to work. Synthetic event is reused for performance reasons in the browser, A synthetic event is a cross-browser wrapper around the browser’s native event it has the same interface as the native event. Synthetic events are delegated to the document node. Therefore native events are triggered first and the events bubble up to document, after which the synthetic events are triggered. The synthetic event object will be reused and all the properties will be nullified after the event callback has been invoked and this is for performance reasons.The workflow of synthetic event in react is:    Element ---- > Event ---- > synthetic event  ---- > handler(e)                                |                                                      |                                |  _______  Component ________|  umber timeStamp The Basics of React Event Handling Let’s explore how to handle events in react and we will showcase the click event and how it holds good for other types of events. Let’s start with functional components by creating a  file as clickAppHandler.js.In this file let’s create a  functional component  as shown below                        Import React from ‘...react’                         function clickAppHandler() {                                function clickHandler() {                                        console.log(‘clicked’)                                         }                                  return (                                                                                  Click                                                                          )                         }                       export default clickAppHandler  When onClick event triggers clickHandler function is called as shown below and when you click the button console will print the string “clicked” After this you need the add a component in the app component. In our code above you can see on click we pass the function as event handler and you will notice that we haven't added parentheses as it becomes a function, and we do not want that and we want handler to be a function not a function call. When a new component is rendered its event handler functions are added to the mapping maintained by the react.When the event is triggered and it hits and DOM object ,react maps the event to the handler, if it matches it calls the handler. 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