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React Router: Routing Mechanism in ReactJS

When designing a website, it is essential to be able to load different pages or modules, or to navigate to another page as per the context. React Router is the tool that supports these tasks. When implementing React Router, you may come across some issues and common problems. In this blog, we will talk about routing techniques and the underlying mechanisms.React is an extremely popular library used to create single page applications (SPAs). We can have multiple views and components in the same page, therefore, to navigate through the whole application we need to use React Router.In this post we will focus on the problems involved in using React Router, and will help you to understand the solutions.You will learn the following:IntroductionBasic RoutingHow Routing Works / Routing MechanismComponents in React Router and their explanationInstallation and StepsSource Codes and SnippetsChallenges and DebuggingConclusionIn this blog, we are using react-browser-router 2.1.2. You can check the official documentation here.In the official documentation and the API, it is mentioned as the Browser Router, but we will use the word “Router” as it can be technically aliased.1. Introduction: React Router (Browser Router)React does not provide the facility of routing when we create the react app initially. We must install it manually in our application using a package manager (npm or yarn). Later we will learn how to enable routing in our React application, but before that we need to understand the core concepts.Whenever a user changes the URL of the website, an HTTP request is sent to the server. The server recognizes the request and returns some responses, which can be a webpage or data in some forms (JSON objects, texts etc.)  The user may be redirected to another page and some other component in the same page may be loaded.Let us take an example – when a user types a URL “localhost:3000/home”, the home page of the website should open; similarly, if the user types “localhost:3030/contact” then the contact page of the website should open. Also, if a user types some random or invalid URL, an error page or some error message should appear.React Router makes it easier for the developers to implement this approach very effectively.2. Basic RoutingThe main task of routing is to load a specific page on targeting a specific URL or path. Loading a specific page on hitting a specific URL is called basic routing. It is quite easy to jump to another page, but it can get complicated when we try to render the components inside the same page. In this state, the page does not get refreshed and therefore there is less interaction with the server; and the performance of the application is increased as the server-side rendering is reduced.  3. How Routing Works / Routing mechanismWhen we implement router in our react application, we are either looking to move to another page or load other components in the same page. To move to another page, we usually use Link inside the browser router. To load a component inside the same page, we use Route and specify the path and the component name.Inside the Router, we use Switch to switch between the different routing paths.We can use Link and Route together to load a particular component.Route is for a specific path and a particular component. Therefore, whenever a particular path is triggered, the associated component must be rendered. To use the components, we need to import them in the same file where we are using the Router.4. Components in React Router and their explanation<BrowserRouter> and <HashRouter>To handle the static requests, we use HashRouter and to handle the dynamic requests, we use BrowserRouter. We will focus on BrowserRouter in the later steps. A BrowserRouter uses regular URLs.<Route> and <Switch> Switch gives us the facility to switch between the different Routes. If no matching Route is found then the Switch renders nothing.<Link>, <NavLink> and <Redirect> To create a link in our application, react provides a Link component. On the other hand, we can say that whenever we use the Link component simply <a> (an Anchor) is rendered in the HTML document. NavLink is a special type of Link. If we want to force a particular navigation, we can use Redirect.  To know more about these components, please visit the following links.5. Installation and the stepsYou must be clear with the fact that when we create a react app, the browser router is not pre-installed. So, we need to add it in the application by using npm. To implement the routing in our application, first we will create an app and make some required changes in the further steps. Let us do this from scratch.These are the essential steps which we can follow:Step #1 Create a react App:npx create-react-app my-appIf you have npm version 6+ then you can simply typenpm init react-app my-appStep #2 Move to the Directorycd my-appStep #3 Launch the appnpm startStep #4 Add Browser Router in our applicationnpm install --save react-router-domStep #5 Go to package.json and verify that the Browser Router is installed in our app6. Source codes and snippetsNow our basic project is ready and we have successfully added the Browser Router package in our application. We need to import the relevant API from the react-router-dom library to make it work.Let us move ahead and implement the rest of the steps:Step #6 Remove the unnecessary codes from the App.js. We have the following codes now:import React from 'react'; import './App.css'; function App() { return ( <div className="App"> </div> ); } export default App;Step #6 Create three JS files - Home.js, Contact.js and Feedback.jsimport React from "react"; const Home = () => { return ( <div> <h 1>This is Home Page!</h1> </div> ); }; export default Home;import React from "react"; const Contact = () => { return ( <div> <h1>This is Contact Page!</ h1> </div> ); }; export default Contact;import React from "react"; const Feedback = () => { return ( <div> <h1>This is Feedback Page!</ h1> </div> ); }; export default Feedback;Step #7 Import all the files in App.js file and start the app. You will find this output on the browser:import React from 'react'; import './App.css'; import Home from './Home'; import Contact from './Contact'; import Feedback from './Feedback'; function App() { return ( <div className="App"> <Home/> <Contact/> <Feedback/> </div> ); } export default App;Step #8 Now we can add the Routing part, and make some changes in the App.jsimport React from "react"; import "./App.css"; import Home from "./Home"; import Contact from "./Contact"; import Feedback from "./Feedback"; import { BrowserRouter, Route, Link } from "react-router-dom"; function App() { return ( <div className="App"> <BrowserRouter> <div style={{ display : "flex"}}> <li> <Link to="/">Home</Link> </li> <li> <Link to="/contact">Contact</Link> </li> <li> <Link to="/Feedback">Feedback</Link> </li> </div> <Route path="/" exact component={Home} /> <Route path="/contact" component={Contact} /> <Route path="/feedback" component={Feedback} /> </BrowserRouter> </div> ); } export default App;Explanation: Look at the App.js file carefully. We have added the Link and Route inside the Browser router which says that whenever a user clicks on the link, it renders a specific component from the given path which we have mentioned in the Route.By default, the home page is selected. Do not forget to put exact keywords (parameters) for the home Route as it disables the partial matching for a route. You can play around with the code and find out some interesting observations.You can see in the address bar that whenever we click on the Contact and Feedback link, their respective URLs are reflected in the address bar. You can manually fill the same URL and trigger it, and it loads the respective pages. It is called basic or simple routing.  7. Challenges and debuggingI have gone through other blogs and tutorials where I have seen that they have aliased the BrowserRouter to Router. So do not get confused with this term. Both are similar and I am sure that you are aware about the Aliases for the packages.You might face issues while using the BrowserRouter, Link and Route and therefore make sure that the package is installed. You can verify it in the package.json file.Make sure that you provide the correct path and component name in the Route.You can find the helpful documentation and resources here.ConclusionIt is amazingly easy to use React Routing in your applications. It makes the UI more appealing and dynamic. You must specify the correct path and the respective components in the route component to make it work correctly. Before implementing the approaches, a basic understanding of the component and the hierarchy of the react components is necessary. There may be changes in the API or in the versions, therefore it is always better to use the official documentation to understand the usage.

React Router: Routing Mechanism in ReactJS

643
React Router: Routing Mechanism in ReactJS 

When designing a website, it is essential to be able to load different pages or modules, or to navigate to another page as per the context. React Router is the tool that supports these tasks. When implementing React Router, you may come across some issues and common problems. In this blog, we will talk about routing techniques and the underlying mechanisms.

React is an extremely popular library used to create single page applications (SPAs). We can have multiple views and components in the same page, therefore, to navigate through the whole application we need to use React Router.

In this post we will focus on the problems involved in using React Router, and will help you to understand the solutions.
You will learn the following:

  1. Introduction
  2. Basic Routing
  3. How Routing Works / Routing Mechanism
  4. Components in React Router and their explanation
  5. Installation and Steps
  6. Source Codes and Snippets
  7. Challenges and Debugging
  8. Conclusion

In this blog, we are using react-browser-router 2.1.2. You can check the official documentation here.
In the official documentation and the API, it is mentioned as the Browser Router, but we will use the word “Router” as it can be technically aliased.

1. Introduction: React Router (Browser Router)

React does not provide the facility of routing when we create the react app initially. We must install it manually in our application using a package manager (npm or yarn). Later we will learn how to enable routing in our React application, but before that we need to understand the core concepts.

React Router

Whenever a user changes the URL of the website, an HTTP request is sent to the server. The server recognizes the request and returns some responses, which can be a webpage or data in some forms (JSON objects, texts etc.)  The user may be redirected to another page and some other component in the same page may be loaded.

Let us take an example – when a user types a URL “localhost:3000/home”, the home page of the website should open; similarly, if the user types “localhost:3030/contact” then the contact page of the website should open. Also, if a user types some random or invalid URL, an error page or some error message should appear.

React Router

React Router makes it easier for the developers to implement this approach very effectively.

2. Basic Routing

The main task of routing is to load a specific page on targeting a specific URL or path. Loading a specific page on hitting a specific URL is called basic routing. It is quite easy to jump to another page, but it can get complicated when we try to render the components inside the same page. In this state, the page does not get refreshed and therefore there is less interaction with the server; and the performance of the application is increased as the server-side rendering is reduced.  

3. How Routing Works / Routing mechanism

When we implement router in our react application, we are either looking to move to another page or load other components in the same page. To move to another page, we usually use Link inside the browser router. To load a component inside the same page, we use Route and specify the path and the component name.

Routing Mechanism in ReactJS 

Inside the Router, we use Switch to switch between the different routing paths.

We can use Link and Route together to load a particular component.

Route is for a specific path and a particular component. Therefore, whenever a particular path is triggered, the associated component must be rendered. To use the components, we need to import them in the same file where we are using the Router.

4. Components in React Router and their explanation

  • <BrowserRouter> and <HashRouter>
    To handle the static requests, we use HashRouter and to handle the dynamic requests, we use BrowserRouter. We will focus on BrowserRouter in the later steps. A BrowserRouter uses regular URLs.
  • <Route> and <Switch> 
    Switch gives us the facility to switch between the different Routes. If no matching Route is found then the Switch renders nothing.
  • <Link>, <NavLink> and <Redirect>
    To create a link in our application, react provides a Link component. On the other hand, we can say that whenever we use the Link component simply <a> (an Anchor) is rendered in the HTML document. NavLink is a special type of Link. If we want to force a particular navigation, we can use Redirect.  
    To know more about these components, please visit the following links.

5. Installation and the steps

You must be clear with the fact that when we create a react app, the browser router is not pre-installed. So, we need to add it in the application by using npm. To implement the routing in our application, first we will create an app and make some required changes in the further steps. Let us do this from scratch.

These are the essential steps which we can follow:

Step #1 Create a react App:

npx create-react-app my-app

If you have npm version 6+ then you can simply type

npm init react-app my-app

Step #2 Move to the Directory

cd my-app

Step #3 Launch the app

npm start

Step #4 Add Browser Router in our application

npm install --save react-router-dom

Step #5 Go to package.json and verify that the Browser Router is installed in our app

Routing Mechanism in ReactJS 

6. Source codes and snippets

Now our basic project is ready and we have successfully added the Browser Router package in our application. We need to import the relevant API from the react-router-dom library to make it work.

Let us move ahead and implement the rest of the steps:

Step #6 Remove the unnecessary codes from the App.js. We have the following codes now:

import React from 'react'; 
import './App.css'; 
function App() { 
  return ( 
    <div className="App"> 
    </div> 
  ); 
} 
export default App;

Step #6 Create three JS files - Home.js, Contact.js and Feedback.js

import React from "react";
const Home = () => { 
  return ( 
    <div> 
      <h 1>This is Home Page!</h1> 
    </div> 
  ); 
}; 
export default Home;
import React from "react";
const Contact = () => {
  return (
    <div>
      <h1>This is Contact Page!</ h1> 
    </div> 
  ); 
}; 
export default Contact;
import React from "react";
const Feedback = () => {
  return (
    <div>
      <h1>This is Feedback Page!</ h1>
    </div>
  );
};
export default Feedback;

Step #7 Import all the files in App.js file and start the app. You will find this output on the browser:

import React from 'react';
import './App.css';
import Home from './Home';
import Contact from './Contact';
import Feedback from './Feedback';
function App() {
  return (
    <div className="App">
    <Home/>
    <Contact/>
    <Feedback/>
    </div>
  ); 
}
export default App;

Routing Mechanism in ReactJS Step #8 Now we can add the Routing part, and make some changes in the App.js

import React from "react";
import "./App.css";
import Home from "./Home";
import Contact from "./Contact";
import Feedback from "./Feedback";
import { BrowserRouter, Route, Link } from "react-router-dom";
function App() {
  return (
    <div className="App">
      <BrowserRouter>
        <div style={{ display : "flex"}}>
          <li>
            <Link to="/">Home</Link>
          </li>
          <li>
            <Link to="/contact">Contact</Link>
          </li>
          <li>
            <Link to="/Feedback">Feedback</Link>
          </li>
        </div>
        <Route path="/" exact component={Home} />
        <Route path="/contact" component={Contact} />
        <Route path="/feedback" component={Feedback} />
      </BrowserRouter>
    </div>
  );
}
export default App;

Routing Mechanism in ReactJS Routing Mechanism in ReactJS 

Routing Mechanism in ReactJS 
Explanation: Look at the App.js file carefully. We have added the Link and Route inside the Browser router which says that whenever a user clicks on the link, it renders a specific component from the given path which we have mentioned in the Route.

By default, the home page is selected. Do not forget to put exact keywords (parameters) for the home Route as it disables the partial matching for a route. You can play around with the code and find out some interesting observations.

You can see in the address bar that whenever we click on the Contact and Feedback link, their respective URLs are reflected in the address bar. You can manually fill the same URL and trigger it, and it loads the respective pages. It is called basic or simple routing.  

7. Challenges and debugging

I have gone through other blogs and tutorials where I have seen that they have aliased the BrowserRouter to Router. So do not get confused with this term. Both are similar and I am sure that you are aware about the Aliases for the packages.
You might face issues while using the BrowserRouter, Link and Route and therefore make sure that the package is installed. You can verify it in the package.json file.

Make sure that you provide the correct path and component name in the Route.

You can find the helpful documentation and resources here.

Conclusion

It is amazingly easy to use React Routing in your applications. It makes the UI more appealing and dynamic. You must specify the correct path and the respective components in the route component to make it work correctly. Before implementing the approaches, a basic understanding of the component and the hierarchy of the react components is necessary. There may be changes in the API or in the versions, therefore it is always better to use the official documentation to understand the usage.

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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