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What Is the Relationship Between Node.Js and V8?

In this article, we will look into Node.js and V8. Node.js is a very important part of the JavaScript ecosystem, as it is used in the backend to produce a complete application. It is often considered a part of the popular MERN(MongoDB, ExpressJS, ReactJS and Node.js) stack and MEAN (MongoDB, ExpressJS, Angular and Node.js) stack. The V8 engine is what powers Node.js and it is an open-source engine on which even Chrome works. It parses and runs your JavaScript inside a Node environment. Overview on Node.jsNode.js was created by Ryan Dahl in 2009 and since then it has become a very popular backend technology. Till then the backend was dominated by languages like PHP, ASP.NET and Java. It has become popular because it enables a Frontend developer with JavaScript skills to easily create full stack apps.The formal definition on the official Node.js website describes Node.js as “a JavaScript runtime built on Chrome’s V8 JavaScript engine.”Node.js came into existence when its creator Ryan Dahl, understanding the power of V8, powered the Chrome browser and extended it so that it can run on your machine as a standalone application. Another part of the definition on the official Node.js website says,Node.js uses an event driven, non-blocking I/O model that makes it lightweight and efficient.I/O refers to input/output and this is where the additional functionality of Node.js comes into play. We can read and edit local files in Node.js and also do an HTTP request to an API. The earlier backend systems like PHP and ASP used to block the program till a network request was complete. But it was completely changed by Node.JS, which sends the request and then goes to the next line of code. So, it is non-blocking and faster than the earlier backend technologies. But it is a single-threaded technology and that is where it has some limitations, whereas Java shines because of it being multi-threaded. Yet another part of the official definition on the Node.js website says,Node.js package ecosystem, npm is the largest ecosystem of open-source libraries in the world. Over the past decade, an amazing community of open-source enthusiasts have created more than 1 million npm packages, which enhance the capabilities of Node.js.It is completely open-source and anyone can use it, as it has an MIT licence, for developing server-side and networking applications. It can run on all three Operating Systems i.e., Mac OS, Windows, and Linux.Overview on V8 JavaScript engineV8 is Google’s open-source JavaScript engine, which is written in C++. It was developed in 2008 for Google Chrome and Chromium based browsers (like Brave), but was used to build Node.js for server-side coding. In fact, the V8 engine, is also used by JSON based No-SQL databases like Couchbase and the popular MongoDB. Besides this, V8 also powers the popular desktop application framework Electron and the latest server-side runtime environment of Deno. V8 is a JavaScript engine, because it takes our JavaScript and executes it while browsing in Chrome. It actually provides a runtime environment in which JavaScript executes. The great thing about this is that the JavaScript engine is independent of the browser in which it executes. This is the feature that prompted the creator of Node.JS to choose V8 engine to power Node.JS and the rest is history. The popularity of Node.JS exploded and the V8 engine was also used to create desktop frameworks and databases.There are other JavaScript engines like SpiderMonkey used by Firefox, and JavaScript Core used by Safari. Microsoft’s Edge was originally based on Chakra JavaScript engine, but has been recently re-built with Chromium and V8 engine.How V8 Engine works A JavaScript Engine is an interpreter which executes JavaScript code. We can create JavaScript engine in two ways – the first way is to implement as a standard interpreter which is done by SpiderMonkey from Mozilla. The other way is the Just-in-time (JIT) compilation, which converts the native JavaScript code to machine code and that is the way V8 uses it. So, the difference between V8 code and others is that it does not produce any intermediate code. When a developer or program runs a JavaScript on V8(i.e. in browser or Node environment), the Ignition interpreter compiles the JavaScript code and generates non-optimized machine code. On runtime, the machine code is analyzed and re-compiled for best performance, by the Turbofan and Crankshaft components of V8. The V8 engine also uses some other components, along with the ones we had seen above. They are Liftoff and Orinoco– Liftoff is responsible for machine code generation in a highly optimized way. It generates code for each opcode and perform way better then Turbofan.Orinoco is responsible for garbage collection. It looks for disconnected memory allocations and perform operations to free up more space. It also update the pointers to new memory locations.V8 also uses a lot of different threads and they are – The primary thread fetches and compiles the JavaScript code.There is another thread which is used to optimize the running code, while the primary thread continues its execution. Yet another thread is used for profiling, which tells on runtime the methods that are needed to be optimized. Some of the threads also do garbage collection.The Just-in-Time ParadigmWe will learn a bit more about the Just-in-Time (JIT) compilation in V8. For a code to execute in any programming language, it must be converted into machine code, which the computer understands. There is a different paradigm for this transformation. Most of the traditional languages created before JavaScript like C++ and Java, perform something called Ahead-of-Time compilation. Here, the code is transformed into machine code before the execution of our program during compile time. Anyone who has worked with Java or C++ knows that we run commands like below to compile a Java or C++ program.javac MyJavaProgram.java  g++ -o mycppprogram mycppprogram.cpp This converts the code into machine code after which we can run our program with commands like below.  java MyJavaProgram  ./mycppprogram On the other hand, in languages like JavaScript and Python, each line of code is executed at runtime. This is done because it is impossible to know the exact code before execution. In a browser, you never compile a code first and then run it, because it is done automatically behind the scenes.So, the Ahead-of-Time compilation produces more optimized and fast code, because of the compilation done before hand. Which is why interpretation done by languages like JavaScript are slower.To overcome this problem in dynamic languages, the approach of Just-in-Time (JIT) compilation, was created, which combines the best of both interpretation and compilation. So, an interpretation step runs before the compilation step, where the V8 engine detects the more frequently used functions and code and compiles them using information from previous executions.During compile time, this code is re-compiled for optimal performance.What is the relationship between Node and V8?The Node.js is referred to as a runtime environment, which includes everything you need to run a program written in JavaScript.The core powering Node.js is this V8 engine. The diagram shows a comparison with the Java Virtual Machine (JVM), which power the Java Runtime environment. Beside the V8 engine the Node.js runtime environment adds many Node APIs to power the Node.js environment. We can also extend the functionality of our node code by installing additional npm packages.One thing to understand is that V8 is essentially an independent C++ library, that is used by Node or Chromium to run JavaScript code. V8 exposes an API that other code can use, so if you have your own C++ program, you can embed V8 in it and run a JavaScript program. That is how it is done by Node and Chrome.Suppose, we want to add a functionality in our JavaScript code to have statements like print(‘hello world’), in addition to the console.log(‘Hello World’). We can add our own implementation of print function in C++, in V8, which is anyway open sourced. Can Node.js work without V8?The current Node.js engine cannot work without V8. It would have no JavaScript engine and hence no ability to run any JavaScript code. The fact is that the native code bindings, which come with Node.js like the fs module and the Net module, rely on the V8 interface between C++ and JavaScript.  Although in the tech world everything is possible and Microsoft in July 2016, made an effort to use Chakra JavaScript engine (which was used in Edge browser at that time) in Node.js and replace the V8 engine,  that project never took off and Microsoft Edge itself recently moved to Chromium, which uses V8 JavaScript engine.The new kid on the block for server-side programming is DENO. Many consider that it could be a replacement to Node.js in the next 2-3 years, and it also uses V8 JavaScript engine under its hood.Summary We have got an overview of Node.js runtime environment and V8 JavaScript engine in this post. Then, we have gone through the working of the V8 engine. We also investigated details of the Just-in-Time compilation, used by V8 JavaScript engine. Also, we have understood the relationship between Node.js and V8 engine and how V8 engine is independent of Node.js.Lastly, we have learnt that it is not possible for Node.js to run without a JavaScript engine like V8. It can, however, be replaced by another JavaScript engine like Chakra from Microsoft; even though this is highly improbable,  it is still possible. 

What Is the Relationship Between Node.Js and V8?

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What Is the Relationship Between Node.Js and V8?

In this article, we will look into Node.js and V8. Node.js is a very important part of the JavaScript ecosystem, as it is used in the backend to produce a complete application. It is often considered a part of the popular MERN(MongoDB, ExpressJSReactJS and Node.js) stack and MEAN (MongoDB, ExpressJS, Angular and Node.js) stack. 

The V8 engine is what powers Node.js and it is an open-source engine on which even Chrome works. It parses and runs your JavaScript inside a Node environment. 

Overview on Node.js

Node.js was created by Ryan Dahl in 2009 and since then it has become very popular backend technology. Till then the backend was dominated by languages like PHP, ASP.NET and Java. It has become popular because it enables a Frontend developer with JavaScript skills to easily create full stack apps.

The formal definition on the official Node.js website describes Node.js as “a JavaScript runtime built on Chrome’s V8 JavaScript engine.

Node.js came into existence when its creator Ryan Dahl, understanding the power of V8, powered the Chrome browser and extended it so that it can run on your machine as a standalone application. 

Another part of the definition on the official Node.js website says,Node.js uses an event driven, non-blocking I/O model that makes it lightweight and efficient.

I/O refers to input/output and this is where the additional functionality of Node.js comes into play. We can read and edit local files in Node.js and also do an HTTP request to an API. 

The earlier backend systems like PHP and ASP used to block the program till a network request was complete. But it was completely changed by Node.JS, which sends the request and then goes to the next line of code. So, it is non-blocking and faster than the earlier backend technologies. 

But it is a single-threaded technology and that is where it has some limitations, whereas Java shines because of it being multi-threaded. 

Yet another part of the official definition on the Node.js website says,Node.js package ecosystem, npm is the largest ecosystem of open-source libraries in the world. 

Over the past decade, an amazing community of open-source enthusiasts have created more than 1 million npm packages, which enhance the capabilities of Node.js.

It is completely open-source and anyone can use it, as it has an MIT licence, for developing server-side and networking applications. It can run on all three Operating Systems i.e., Mac OS, Windows, and Linux.

Overview on V8 JavaScript engine

V8 is Google’s open-source JavaScript engine, which is written in C++. It was developed in 2008 for Google Chrome and Chromium based browsers (like Brave), but was used to build Node.js for server-side coding. In fact, the V8 engine, is also used by JSON based No-SQL databases like Couchbase and the popular MongoDB. Besides this, V8 also powers the popular desktop application framework Electron and the latest server-side runtime environment of Deno. 

V8 is JavaScript engine, because it takes our JavaScript and executes it while browsing in Chrome. It actually provides a runtime environment in which JavaScript executes. The great thing about this is that the JavaScript engine is independent of the browser in which it executes. This is the feature that prompted the creator of Node.JS to choose V8 engine to power Node.JS and the rest is history. The popularity of Node.JS exploded and the V8 engine was also used to create desktop frameworks and databases.

There are other JavaScript engines like SpiderMonkey used by Firefox, and JavaScript Core used by Safari. Microsoft’s Edge was originally based on Chakra JavaScript engine, but has been recently re-built with Chromium and V8 engine.

How V8 Engine works 

A JavaScript Engine is an interpreter which executes JavaScript code. We can create JavaScript engine in two ways – the first way is to implement as a standard interpreter which is done by SpiderMonkey from Mozilla. The other way is the Just-in-time (JIT) compilation, which converts the native JavaScript code to machine code and that is the way V8 uses it. So, the difference between V8 code and others is that it does not produce any intermediate code. 

When a developer or program runs a JavaScript on V8(i.e. in browser or Node environment), the Ignition interpreter compiles the JavaScript code and generates non-optimized machine code. On runtime, the machine code is analyzed and re-compiled for best performance, by the Turbofan and Crankshaft components of V8. 

The V8 engine also uses some other components, along with the ones we had seen above. They are Liftoff and Orinoco 

  • Liftoff is responsible for machine code generation in a highly optimized way. It generates code for each opcode and perform way better then Turbofan.
  • Orinoco is responsible for garbage collection. It looks for disconnected memory allocations and perform operations to free up more space. It also update the pointers to new memory locations.

V8 also uses a lot of different threads and they are – 

  • The primary thread fetches and compiles the JavaScript code.
  • There is another thread which is used to optimize the running code, while the primary thread continues its execution. 
  • Yet another thread is used for profiling, which tells on runtime the methods that are needed to be optimized. 
  • Some of the threads also do garbage collection.

The Just-in-Time Paradigm

We will learn a bit more about the Just-in-Time (JIT) compilation in V8. For a code to execute in any programming language, it must be converted into machine code, which the computer understands. There is a different paradigm for this transformation. 

Most of the traditional languages created before JavaScript like C++ and Java, perform something called Ahead-of-Time compilation. Here, the code is transformed into machine code before the execution of our program during compile time. Anyone who has worked with Java or C++ knows that we run commands like below to compile a Java or C++ program.

javac MyJavaProgram.java 
g++ -o mycppprogram mycppprogram.cpp 

This converts the code into machine code after which we can run our program with commands like below.  

java MyJavaProgram 
./mycppprogram 

On the other hand, in languages like JavaScript and Python, each line of code is executed at runtime. This is done because it is impossible to know the exact code before execution. In a browser, you never compile a code first and then run it, because it is done automatically behind the scenes.

So, the Ahead-of-Time compilation produces more optimized and fast code, because of the compilation done before hand. Which is why interpretation done by languages like JavaScript are slower.

To overcome this problem in dynamic languages, the approach of Just-in-Time (JIT) compilation, was created, which combines the best of both interpretation and compilation. So, an interpretation step runs before the compilation step, where the V8 engine detects the more frequently used functions and code and compiles them using information from previous executions.

During compile time, this code is re-compiled for optimal performance.

What is the relationship between Node and V8?

The Node.js is referred to as a runtime environment, which includes everything you need to run a program written in JavaScript.

The core powering Node.js is this V8 engine. The diagram shows a comparison with the Java Virtual Machine (JVM), which power the Java Runtime environment. Beside the V8 engine the Node.js runtime environment adds many Node APIs to power the Node.js environment. We can also extend the functionality of our node code by installing additional npm packages.relationship between Node and V8

One thing to understand is that V8 is essentially an independent C++ library, that is used by Node or Chromium to run JavaScript code. V8 exposes an API that other code can use, so if you have your own C++ program, you can embed V8 in it and run a JavaScript program. That is how it is done by Node and Chrome.

Suppose, we want to add a functionality in our JavaScript code to have statements like print(‘hello world’), in addition to the console.log(‘Hello World’). We can add our own implementation of print function in C++, in V8, which is anyway open sourced. 

Can Node.js work without V8?

The current Node.js engine cannot work without V8. It would have no JavaScript engine and hence no ability to run any JavaScript code. The fact is that the native code bindings, which come with Node.js like the fs module and the Net module, rely on the V8 interface between C++ and JavaScript.  

Although in the tech world everything is possible and Microsoft in July 2016, made an effort to use Chakra JavaScript engine (which was used in Edge browser at that time) in Node.js and replace the V8 engine that project never took off and Microsoft Edge itself recently moved to Chromium, which uses V8 JavaScript engine.

The new kid on the block for server-side programming is DENO. Many consider that it could be a replacement to Node.js in the next 2-3 years, and it also uses V8 JavaScript engine under its hood.

Summary 

We have got an overview of Node.js runtime environment and V8 JavaScript engine in this post. Then, we have gone through the working of the V8 engine. We also investigated details of the Just-in-Time compilation, used by V8 JavaScript engine. Also, we have understood the relationship between Node.js and V8 engine and how V8 engine is independent of Node.js.

Lastly, we have learnt that it is not possible for Node.js to run without a JavaScript engine like V8. It can, however, be replaced by another JavaScript engine like Chakra from Microsoft; even though this is highly improbable,  it is still possible. 

Nabendu

Nabendu Biswas

Author

Nabendu Biswas is a Full Stack JavaScript Developer, who has been working in the IT industry for the past 16 years and has worked for world’s top development firms, and Investment banks. He is a passionate tech blogger. He is also a tech youtuber and loves to teach people JavaScript. He is also an Apress author with three Gatsby books published. 

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

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

MongoDB Query Document Using Find() With Example

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

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

Implementing MongoDb Map Reduce using Aggregation

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

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