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Introduction to Web APIs in JavaScript

Before we talk about APIs in JavaScript and how to use them, we need to know what exactly we mean by APIs. API stands for Application Programming Interface and is a concept that is not limited or specific to JavaScript, but is used in almost all web application languages. Being a web developer, it is expected that you know about API, so let’s try to understand the concept first. As a concept, API has been there since more than 50 years, but in recent years it has become very popular and has outlined a different method for how we create our applications. Now imagine you are creating a web application where users can sign up and talk about their recent travels, write stories, post pictures and share them. As an add-on they should be able to share the same across multiple platforms like Facebook, Instagram etc. How do we do that? We don’t have access to the Instagram application or their data. We don’t know how they are managing their data and whether data from our application will fit into their databases.  Let’s try to imagine how Instagram would allow add-on without APIs. Perhaps we might drop an email to Instagram asking them to allow us access to their databases where we can write content. They may have received millions of other such requests from people who also need to use Instagram add-ons. Instagram will go through our requests and the million others and probably would use a lucky draw to decide who gets access to their databases. This is obviously not a reasonable solution and without any reasonable solution all applications in the world will just become isolated; which means they can’t communicate and can’t support each other’s features. Luckily our imagination is just that!Fortunately, we are living in a world with APIs around us which allow us to easily communicate with other apps. I can create an application where I can use Google’s search, Facebook’s feed, Instagram’s post, twitter’s tweets all in one app. This is all possible using API. As the name suggests, it allows us to open an interface which can then be used by other apps to communicate using the interface. How does an API work?The purpose of API is to communicate between apps with each other as intermediary, where both apps might have been built with different tools and technologies. It can be achieved by using api standards like REST, SOAP which outline protocols or sets of rules which the client (who needs to call) and server (who serves client’s requests) need to follow. These standards are key to communication. These standards outline what a request should look like and the format in which client should expect response from server. Every api exposes its endpoints (also called entrypoints), which allows its client to use it to access features of apis. For example, in JavaScript, to work with DOM, it exposes Document as an entrypoint in order to work with multiple methods. It allows its client to use it in order to manipulate DOM. In JavaScript however we use containers, which are nothing but HTML controls which can call APIs and response can be rendered within that control. JavaScript: An Introduction JavaScript is one of the most widely used programming languages, even though it is mainly used on browsers to render HTML and CSS. It can also run on our servers to handle client requests, connect with databases and do almost everything any other programming language does on the server. This makes it a significant tool that needs to be learned. Here, we are going to discuss about APIs which are provided by JavaScript to work with almost every aspect of a web application. APIs in JavaScript JavaScript, being a very widely used programming language has a very large set of APIs available, which make a JavaScript developer’s life a lot easier. JavaScript is also a multi-purpose language which means it can not only work on browsers, but also on servers or phones. To support different platforms, it has a different set of APIs to work with. It also provides a rich set of controls and other features like storage on client which are all easily availed by JavaScript.  Browser APIs in JavaScript Browsers use JavaScript to display web pages, handle user interactions, send requests to servers and to receive responses. To make all this possible, JavaScript provides browser APIs which can be used to perform browser related functions:  Working with DOM  DOM stands for Document Object Model, which is a structure that holds all HTML controls on a web page. It not only holds but also allows us to add remove controls from it. You might have worked with document API which is used to get, push or even remove elements from DOM, all of this is coming from JavaScript DOM API. Example: document.getElementById(“header”).text(“This is a header”); Request data from server JavaScript is widely used to optimize web pages by updating only a part of a webpage instead of loading the entire page. for example, when you like a post on Facebook, it doesn’t load the entire page again, it only updates that particular post. Similarly, when we tweet on Twitter it doesn’t reload the entire page to show new tweets. This is how JavaScript makes partial calls to the server using popular fetch, AJAX apis. Example: const response= await fetch(url); // when response is success which is status 200 if (response.ok) {     // receive response from server.   let json = await response.json(); } else {   // if there are errors returned by server, show the error   alert("Error occured" + response.status); }Store data at client Even though we have our databases working smoothly on servers processing terabytes of data every day, you might still want to store a chunk of data on the client’s browsers to optimize the application performances. How do we do that? Again JavaScript will show us the way, by providing APIs like localStorage, sessionStorage which we can use to store data on client’s browser and remove it whenever we want. The difference between localStorage and sessionStorgae is that data which we store in localStorage persists even after closing the browser or tab,  whereas data stored in sessionStorage gets cleared as soon as the tab or browser is closed. Now both of these have its own advantages depending on your requirement.sessionStorage.setItem('key', value); sessionStorage.getItem('key')   localStorage.setItem('key', value); sessionStorage.getItem('key';)Work with Graphics There are lot of popular applications where you might have seen  2D or 3D graphics created using user’s interaction allowing users to create such drawings, and I am not talking about just CSS (Cascaded Style Sheets). Yes, CSS has its role to play, but to allow users to create 2D/3D drawings on the web we need more than just CSS. JavaScript provides canvas api which can be used to work with pixels on web page to draw 2D/ 3D images which will be within <canvas> html tag.Third Party APIs.  Integration with other applications, the structures of which we don’t have much information about, can be difficult. But JavaScript allows us to integrate with many popular third-party apps like Twitter, YouTube, Facebook. For example, you have your company’s website where you also want to display recent tweets that your company’s Twitter account has tweeted. How do we do that? JavaScript’s Twitter API is the answer. This is not only for Twitter, but a lot of other popular apps can be integrated into your own web page using JavaScript’s third party APIs. Web Audio API  Audio API in JavaScript provides a smooth implementation of audio controls over a webpage. This includes multiple play controls on audio, and audio effects on the web. Web Audio API has multiple interfaces which include operations related to visualization effects, audio destinations, merging audio channels and audio processing. Example <div>   <audio src="myfavsong.mp3"></audio>   <button>Play</button>   <input type="range" min="0" max="1" step="0.01" value="1"> </div>Geolocation APIThere are many web apps which work best with information of user’s locations, for example, if you are looking for restaurants nearby, you will get better results if Google knows your location. It is obviously up to the user’s consent if they want to share their location or not due to privacy concerns, but if they do want to share, geolocation API provides location of users to web applications. Example: var address = document.getElementById("address"); function accessUserLocation() {   if (navigator.geolocation) { navigator.geolocation.getCurrentPosition(displayLocation); } } function displayLocation(location) { address.innerHTML = "Latitude: " + location.coords.latitude +   "Longitude: " + location.coords.longitude;   }History API  History API is another useful although rarely used API, used if you want to allow user to traverse back and forth on a web application. History API runs with window objects using three different methods available-- go, back and forward. Example: // Visit page visited previously  window.history.back();  // Traverse to forward on web page.  window.history.forward();  // Move forward by 1 page  window.history.go(1); Web Workers API  Workers can be created using constructors in JavaScript, which can run a JavaScript file under worker thread context, which is different from the context of windows in JavaScript. There are a few exceptions on what kind of code we can run under worker thread, for example we can’t manipulate DOM using worker thread. With this a question arises-- if worker thread is different form main window thread, then how do they communicate? Because even though it is running in a different thread, the worker can still execute many window methods. To make this possible, the worker and main thread communicate using postMessage() method; to send data whenever onmessage event is called and handled. Example: const worker = new Worker('input.js'); Here input file which is a JavaScript file will contain the code which you need the worker thread to execute. Most Popular JavaScript APIs Browser APIs – We have discussed them in detail and since JavaScript leads how web applications are rendered on browser, the popularity of browser APIs is obvious. Canvas APIs – This is another favorite API of many developers who work in the graphics domain and need interactive applications for their client to easily work with drawings and graphics on web pages. SocialMedia APIs – This is very common nowadays. Any web application that targets an audience, needs social media integrations in their app, such as Facebook, Twitter, Instagram APIs, where they can showcase recent activities on their web page. Storage APIs – Every site I browse now a days pops up a panel asking me to accept cookies settings. Why? Because it helps the applications work well with user’s interaction and responses to the app, and the storage is not limited to cookies. sessionStorage and localStorage are widely used in JavaScript applications to store user’s info on client’s browsers. We just can’t imagine a life without storage APIs in JavaScript! JavaScript tools and relationship between themJavaScript Libraries There are JavaScript libraries like jQuery and React which implement JavaScript with their own new syntax. For example, the way we access our DOM using vanilla JavaScript and the way jQuery does it is different, but in the end, both use the same API which we have discussed above. Another example is when using React, where it extends JavaScript with JSX to embed JavaScript with HTML in React components.JavaScript FrameworksJavaScript Frameworks like Angular and Vue make most of the JavaScript APIs as they are built on top of JavaScript. The difference between the frameworks is in the structure, data flow and different patterns which they use to make it easier to work with JavaScript and implement its APIs.  For example, Angular uses Dependency Injection to inject services into the component’s constructors, making it a sophisticated form of implementing inversion control which would be not this smooth with vanilla JavaScript. Frameworks like Angular try to prevent users from manipulating DOM directly as it is an expensive operation. However, it doesn’t mean it doesn’t update DOM at all. In the end, Angular uses DOM manipulation internally in quite an effective way, using the same APIs we have discussed above.Conclusion An API can be compared to a phone with unlimited talk time that is given to an application, allowing it to communicate with all other applications in the world. Why do we need this? Because one application doesn’t need to and can’t do everything. They need each other’s help. APIs can be for external as well internal use. External APIs allows an app to communicate with other apps, and internal or built-in APIs allow developers to work effectively with the tools. JavaScript being the most popular language in the world is aware of this and hence presents plenty of interfaces for us as developers to use in our applications. Be it working with storage, creating controls, integrating with Twitter, presenting media, or drawing graphics, JavaScript will not let you down.  

Introduction to Web APIs in JavaScript

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Introduction to Web APIs in JavaScript

Before we talk about APIs in JavaScript and how to use them, we need to know what exactly we mean by APIs. API stands for Application Programming Interface and is a concept that is not limited or specific to JavaScript, but is used in almost all web application languages. Being a web developer, it is expected that you know about API, so let’s try to understand the concept first. 

As a concept, API has been there since more than 50 years, but in recent years it has become very popular and has outlined a different method for how we create our applications. Now imagine you are creating a web application where users can sign up and talk about their recent travels, write stories, post pictures and share them. As an add-on they should be able to share the same across multiple platforms like Facebook, Instagram etc. How do we do that? We don’t have access to the Instagram application or their data. We don’t know how they are managing their data and whether data from our application will fit into their databases.  

Let’s try to imagine how Instagram would allow add-on without APIs. Perhaps we might drop an email to Instagram asking them to allow us access to their databases where we can write content. They may have received millions of other such requests from people who also need to use Instagram add-ons. Instagram will go through our requests and the million others and probably would use a lucky draw to decide who gets access to their databases. This is obviously not a reasonable solution and without any reasonable solution all applications in the world will just become isolated; which means they can’t communicate and can’t support each other’s features. Luckily our imagination is just that!

Fortunately, we are living in a world with APIs around us which allow us to easily communicate with other apps. I can create an application where I can use Google’s search, Facebook’s feed, Instagram’s post, twitter’s tweets all in one app. This is all possible using API. As the name suggests, it allows us to open an interface which can then be used by other apps to communicate using the interface. 

How does an API work?

The purpose of API is to communicate between apps with each other as intermediary, where both apps might have been built with different tools and technologies. It can be achieved by using api standards like REST, SOAP which outline protocols or sets of rules which the client (who needs to call) and server (who serves client’s requests) need to follow. These standards are key to communication. These standards outline what a request should look like and the format in which client should expect response from server. 

Every api exposes its endpoints (also called entrypoints), which allows its client to use it to access features of apis. For example, in JavaScript, to work with DOM, it exposes Document as an entrypoint in order to work with multiple methods. It allows its client to use it in order to manipulate DOM. In JavaScript however we use containers, which are nothing but HTML controls which can call APIs and response can be rendered within that control. 

JavaScript: An Introduction 

JavaScript is one of the most widely used programming languages, even though it is mainly used on browsers to render HTML and CSS. It can also run on our servers to handle client requests, connect with databases and do almost everything any other programming language does on the server. This makes it a significant tool that needs to be learned. 

Here, we are going to discuss about APIs which are provided by JavaScript to work with almost every aspect of a web application. 

APIs in JavaScript 

JavaScript, being a very widely used programming language has a very large set of APIs available, which make a JavaScript developer’s life a lot easier. JavaScript is also a multi-purpose language which means it can not only work on browsers, but also on servers or phones. To support different platforms, it has a different set of APIs to work with. It also provides a rich set of controls and other features like storage on client which are all easily availed by JavaScript.  

Browser APIs in JavaScript 

Browsers use JavaScript to display web pages, handle user interactions, send requests to servers and to receive responses. To make all this possible, JavaScript provides browser APIs which can be used to perform browser related functions:  

  1. Working with DOM  

DOM stands for Document Object Model, which is a structure that holds all HTML controls on a web page. It not only holds but also allows us to add remove controls from it. You might have worked with document API which is used to get, push or even remove elements from DOM, all of this is coming from JavaScript DOM API. 

Example: document.getElementById(“header”).text(“This is a header”); 

  1. Request data from server 

JavaScript is widely used to optimize web pages by updating only a part of a webpage instead of loading the entire page. for example, when you like a post on Facebook, it doesn’t load the entire page again, it only updates that particular post. Similarly, when we tweet on Twitter it doesn’t reload the entire page to show new tweets. This is how JavaScript makes partial calls to the server using popular fetch, AJAX apis. 

Example: 

const response= await fetch(url); 
// when response is success which is status 200 
if (response.ok) {   
  // receive response from server. 
  let json = await response.json(); 
} else { 
  // if there are errors returned by server, show the error 
  alert("Error occured" + response.status); 
}
  1. Store data at client 

Even though we have our databases working smoothly on servers processing terabytes of data every day, you might still want to store a chunk of data on the client’s browsers to optimize the application performances. How do we do that? 

Again JavaScript will show us the way, by providing APIs like localStorage, sessionStorage which we can use to store data on client’s browser and remove it whenever we want. The difference between localStorage and sessionStorgae is that data which we store in localStorage persists even after closing the browser or tab,  whereas data stored in sessionStorage gets cleared as soon as the tab or browser is closed. Now both of these have its own advantages depending on your requirement.

sessionStorage.setItem('key', value); 
sessionStorage.getItem('key')  
localStorage.setItem('key', value); 
sessionStorage.getItem('key';)
  1. Work with Graphics 

There are lot of popular applications where you might have seen  2D or 3D graphics created using user’s interaction allowing users to create such drawings, and I am not talking about just CSS (Cascaded Style Sheets). Yes, CSS has its role to play, but to allow users to create 2D/3D drawings on the web we need more than just CSS. JavaScript provides canvas api which can be used to work with pixels on web page to draw 2D/ 3D images which will be within <canvas> html tag.

Third Party APIs.  

Integration with other applications, the structures of which we don’t have much information about, can be difficult. But JavaScript allows us to integrate with many popular third-party apps like Twitter, YouTube, Facebook. 

For example, you have your company’s website where you also want to display recent tweets that your company’s Twitter account has tweeted. How do we do that? JavaScript’s Twitter API is the answer. This is not only for Twitter, but a lot of other popular apps can be integrated into your own web page using JavaScript’s third party APIs. 

Web Audio API  

Audio API in JavaScript provides a smooth implementation of audio controls over a webpage. This includes multiple play controls on audio, and audio effects on the web. Web Audio API has multiple interfaces which include operations related to visualization effects, audio destinations, merging audio channels and audio processing. 

Example 

<div> 
  <audio src="myfavsong.mp3"></audio> 
  <button>Play</button> 
  <input type="range" min="0" max="1" step="0.01" value="1"> 
</div>

Geolocation API

There are many web apps which work best with information of user’s locations, for example, if you are looking for restaurants nearby, you will get better results if Google knows your location. It is obviously up to the user’s consent if they want to share their location or not due to privacy concerns, but if they do want to share, geolocation API provides location of users to web applications. 

Example: 

var address = document.getElementById("address"); 
function accessUserLocation() { 
  if (navigator.geolocation) { 
navigator.geolocation.getCurrentPosition(displayLocation); 
} 
} 
function displayLocation(location) { 
address.innerHTML = "Latitude: " + location.coords.latitude +   
"Longitude: " + location.coords.longitude;   
}

History API  

History API is another useful although rarely used API, used if you want to allow user to traverse back and forth on a web application. History API runs with window objects using three different methods available-- go, back and forward. 

Example: 

// Visit page visited previously 
window.history.back(); 
// Traverse to forward on web page. 
window.history.forward(); 
// Move forward by 1 page 
window.history.go(1); 

Web Workers API  

Workers can be created using constructors in JavaScript, which can run a JavaScript file under worker thread context, which is different from the context of windows in JavaScript. There are a few exceptions on what kind of code we can run under worker thread, for example we can’t manipulate DOM using worker thread. With this a question arises-- if worker thread is different form main window thread, then how do they communicate? Because even though it is running in a different thread, the worker can still execute many window methods. To make this possible, the worker and main thread communicate using postMessage() method; to send data whenever onmessage event is called and handled. 

Example: 

const worker = new Worker('input.js'); 

Here input file which is a JavaScript file will contain the code which you need the worker thread to execute. 

Most Popular JavaScript APIs 

  • Browser APIs  We have discussed them in detail and since JavaScript leads how web applications are rendered on browser, the popularity of browser APIs is obvious. 
  • Canvas APIs  This is another favorite API of many developers who work in the graphics domain and need interactive applications for their client to easily work with drawings and graphics on web pages. 
  • SocialMedia APIs – This is very common nowadays. Any web application that targets an audience, needs social media integrations in their app, such as Facebook, Twitter, Instagram APIs, where they can showcase recent activities on their web page. 
  • Storage APIs  Every site I browse now a days pops up a panel asking me to accept cookies settings. Why? Because it helps the applications work well with user’s interaction and responses to the app, and the storage is not limited to cookies. sessionStorage and localStorage are widely used in JavaScript applications to store user’s info on client’s browsers. We just can’t imagine a life without storage APIs in JavaScript! 

JavaScript tools and relationship between them

JavaScript Libraries

 There are JavaScript libraries like jQuery and React which implement JavaScript with their own new syntax. For example, the way we access our DOM using vanilla JavaScript and the way jQuery does it is different, but in the end, both use the same API which we have discussed above. Another example is when using React, where it extends JavaScript with JSX to embed JavaScript with HTML in React components.

JavaScript Frameworks

JavaScript Frameworks like Angular and Vue make most of the JavaScript APIs as they are built on top of JavaScript. The difference between the frameworks is in the structure, data flow and different patterns which they use to make it easier to work with JavaScript and implement its APIs.  

For example, Angular uses Dependency Injection to inject services into the component’s constructors, making it a sophisticated form of implementing inversion control which would be not this smooth with vanilla JavaScript. Frameworks like Angular try to prevent users from manipulating DOM directly as it is an expensive operation. However, it doesn’t mean it doesn’t update DOM at all. In the end, Angular uses DOM manipulation internally in quite an effective way, using the same APIs we have discussed above.

Conclusion 

An API can be compared to a phone with unlimited talk time that is given to an application, allowing it to communicate with all other applications in the world. Why do we need this? Because one application doesn’t need to and can’t do everything. They need each other’s help. 

APIs can be for external as well internal use. External APIs allows an app to communicate with other apps, and internal or built-in APIs allow developers to work effectively with the tools. JavaScript being the most popular language in the world is aware of this and hence presents plenty of interfaces for us as developers to use in our applications. Be it working with storage, creating controls, integrating with Twitter, presenting media, or drawing graphics, JavaScript will not let you down.  

Dheeraj

Dheeraj Kumar

Author

Dheeraj is a Full Stack Developer, Trainer and Architect. He has more than 8 years of experience with .NET and JavaScript stacks building enterprise applications. He has trained more than 1000 students and professionals in .Net, MEAN and MERN stack.

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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 
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Implementing MongoDb Map Reduce using Aggregation

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