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How to Install MongoDB on Ubuntu

MongoDB is an open-source document database used in numerous modern Web applications. MongoDB is also known as Mongo. It is classified as a NoSQL database because it does not have a traditional relational database structure based on the table.Unlike relational databases, it uses dynamically based JSON-like documents, meaning that MongoDB requires no predetermined schema before you add data into it. You can change the structure anytime, without setting up a new database update structure.PrerequisitesHardware Requirements:RAM– 1 GB  Storage- 256 GB of Hard Disk SpaceSoftware Requirements:Web Browser: Any browser such as Google Chrome, Mozilla Firefox, Microsoft Edge.Operating System: An Ubuntu 18.04 server installed with a non-root sudo user and firewall.Installation ProcedureStep 1 - Installing MongoDBUbuntu's package repositories contain the latest version of MongoDB.You should include the dedicated MongoDB package repositories in APT sources in order to obtain the latest version of this software. Then you can install the mongodb-org, package which always indicates MongoDB's latest version.1. Use the following command to load the public GPG key for the most recent version of MongoDB. In the URL section of the command, you should change 4.4 with the version you want to install if you intend to use a version of MongoDB other than 4.4:curl -fsSL https://www.mongodb.org/static/pgp/server-4.4.asc | sudo apt-key add -You will get to see ok on the screen if the key was added successfully.curl is a tool on the command line for numerous transmission systems. It reads any data stored on the URL to which it is transferred and shows the content on the output of the system. In this example, cURL displays the GPG key file contents and links it into the following sudo apt-key add - command, adding the GPG key to the keys list.2. This curl command uses the -fsSL options that basically tell cURL to fail silently. That shows that if cURL does not contact the GPG server or the GPG server is down, the error code is not going to be added to the trusted keys list.You can double-check whether the key has been added properly by:$ apt-key listYou will get to see the key in the output like this:Even now,the APT installation doesn’t know where you have to install the latest versions of MongoDB to locate the mongodb-org package.You have two places on the APT Server where you can download and install online package sources: the sources.list file and the directory sources.list.d. The sources.list is a file listing the active APT data sources, with one source for each line. You can also add sources.list.d entries in separate files in the source.list directory.3. Enter the following command, and create a file named mongodb-org-4.4.list in the sources.list.d directory:$ echo "deb [ arch=amd64,arm64 ] https://repo.mongodb.org/apt/ubuntu bionic/mongodb-org/4.4 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-4.4.list4. Upgrade your local server package index to APT to know where to find the mongodb-org package after executing this command:$ sudo apt update5. Now, you can install MongoDB:$ sudo apt install mongodb-orgPress Y and then ENTER to confirm that the package is to be installed.MongoDB is installed on the system when the command is completed. It is not ready to be used, however. Next, you're going to run MongoDB and confirm it works.Step 2 - Running the MongoDB ServiceThe previous step's installation configures MongoDB to run as a daemon maintained by the system, which means you can control MongoDB using different systemctl commands. However, the service will not start automatically with this installation process.1. To start the MongoDB service, you can use the following command:$ sudo systemctl start mongod.service2. Check the status of the service at this point. Systemctl will automatically attach this to any argument passed if there aren't any already, so it is not important to include it:$ sudo systemctl status mongodThis command returns this output, which indicates that the service is running:3. Once the service is confirmed to run as expected, start the MongoDB service:$ sudo systemctl enable mongod4. The database can also be verified by connecting to the database and executing a diagnostic command. The following command will show its current version, server address and port. The response of the internal MongoDB connectionStatus command will also be returned:$ mongo --eval 'db.runCommand({ connectionStatus: 1 })'ConnectionStatus checks back the database connection status and returns it. A value of 1 in the answer for the ok field shows that the server works as expected:Output:Note also that a loopback address of the locally located host is running at port 27017 on 127.0.0.1. This is the default port number for MongoDB.Next, we will examine how to manage the system instance of the MongoDB server.Step 3 - Managing the ServicesAs already mentioned, mongoDB is set up as a system service for the installation process. This means that, as other Ubuntu system services, it can be managed with standard systemctl commands.The systemctl status as previously mentioned, controls MongoDB service status:$ sudo systemctl status mongodTo stop the service:$ sudo systemctl stop mongodTo start the service when it is stopped:$ sudo systemctl start mongodTo restart the server when it is running:$ sudo systemctl restart mongodPreviously we have allowed MongoDB to start the server automatically. If this is required to be disabled, use:$ sudo systemctl disable mongodTo re-activate the boot, execute the enable command again:$ sudo systemctl enable mongodStep 4 - Create MongoDB Database Root User and Password1. MongoDB is deactivated by default, so it started off without access control. Run the following command to start the mongo shell.$ mongo2. You can list all available databases with the command below once you are connected to the mongo shell.> show dbs3. Switch first to the admin database and use the following commands to create the root user.> use admin > db.createUser({user:"root", pwd:"=@!#@%$admin1", roles:[{role:"root", db:"admin"}]})4. Without the --auth command line option the mongodb instance has been started. The authentication of users' needs must be enabled by editing the /lib/systemd/system/mongod.service file.$ sudo nano /lib/systemd/system/mongod.service5. See the ExecStart parameter under the [Service] config section and add --auth as a new option:ExecStart=/usr/bin/mongod --auth --config /etc/mongod.confNow, save the service file and exit nano:6. Reload the systemd services:$ sudo systemctl daemon-reload7. Now restart mongodb and try to connect it:$ sudo service mongod restart8. You must now authenticate yourself as a MongoDB user when you attempt to connect to mongodb. For instance:$ mongo -u "root" -p --authenticationDatabase "admin"Step 5 – Creating an example MongoDB database:1. Create a demo database:1. We will add some data into our demo database. You can use mongo shell to interact with MongoDB instance.  Use the following command to open the mongo shell.$ mongo2. After opening MongoDB prompt, create a new database with the name demoDatabase using the following command:$ use demoDatabaseOutput:Every piece of data in a MongoDB database should be part of a collection. But you don't have to explicitly create a collection. When using the insert method, the collection is automatically created.3.Use the following command to add data into a collection:$ db.myCollection.insert([     {'name': 'Abhresh', 'age': 25},    {'name': 'Ishan', 'age': 20},     {'name': 'Nick', 'age': 30} ]);4. After successful insertion, you will get a message like this in the prompt:Check the database sizeBackups are great if you have large databases, and you need to check the size of your database before creating a backup in order to avoid running out of storage area and thus slowing or crashing your server.  You can use the following commands to check the size:$ db.stats().dataSize;Output:Create a BackupYou have to use the -d option to create a backup of a certain database and specify the database name. In addition, you should use the -o option and indicate a path to let mongodump know where to store the backup.Exit from the mongo shell by using CTRL + D  Use the following commands to create a backup:  $ mongodump -d myDatabase -o ~/backups/first_backupIf the backup is successful, you will get this message:Please note that backup creation is very expensive and can reduce the MongoDB instance performance.We have successfully created a backup of MongoDB database and this shows that MongoDB is perfectly working on Ubuntu system.Uninstall MongoDB from UbuntuTo stop MongoDB first when it is currently being executed, remove MongoDB packages using the Advanced Package Tool, the library's MongoDB databases and the MongoDB log from the log directory.Stop MongoDB Daemon Process$ sudo service mongod stopRemove Packages$ sudo apt-get purge mongodb-org*Remove MongoDB logs$ sudo rm -r /var/log/mongodbThe above command will remove the logs and directories.Remove DatabaseWe will remove the MongoDB from the var/lib/mongodb. Please check if you have MongoDb in any other location, then change the MongoDB location in the command.$ sudo rm -r /var/lib/mongodbLearn more about the core concepts of MongoDB administration, indexes, security, Frameworks with MongoDB Admininstration TrainingConclusionYou added the official MongoDB repository to your APT instance and installed the latest version of MongoDB in this tutorial. You then practiced some systemctl commands and tested Mongo's functionality. This article also helped you to know how to create a backup of the MongoDB database.

How to Install MongoDB on Ubuntu

251
How to Install MongoDB on Ubuntu

MongoDB is an open-source document database used in numerous modern Web applications. MongoDB is also known as Mongo. It is classified as a NoSQL database because it does not have a traditional relational database structure based on the table.

Unlike relational databases, it uses dynamically based JSON-like documents, meaning that MongoDB requires no predetermined schema before you add data into it. You can change the structure anytime, without setting up a new database update structure.

Prerequisites

  • Hardware Requirements:
    • RAM– 1 GB  
    • Storage- 256 GB of Hard Disk Space
  • Software Requirements:
    • Web Browser: Any browser such as Google Chrome, Mozilla Firefox, Microsoft Edge.
    • Operating System: An Ubuntu 18.04 server installed with a non-root sudo user and firewall.

Installation Procedure

Step 1 - Installing MongoDB

Ubuntu's package repositories contain the latest version of MongoDB.

You should include the dedicated MongoDB package repositories in APT sources in order to obtain the latest version of this software. Then you can install the mongodb-org, package which always indicates MongoDB's latest version.

1. Use the following command to load the public GPG key for the most recent version of MongoDB. In the URL section of the command, you should change 4.4 with the version you want to install if you intend to use a version of MongoDB other than 4.4:

curl -fsSL https://www.mongodb.org/static/pgp/server-4.4.asc | sudo apt-key add -

You will get to see ok on the screen if the key was added successfully.

curl is a tool on the command line for numerous transmission systems. It reads any data stored on the URL to which it is transferred and shows the content on the output of the system. In this example, cURL displays the GPG key file contents and links it into the following sudo apt-key add - command, adding the GPG key to the keys list.

2. This curl command uses the -fsSL options that basically tell cURL to fail silently. That shows that if cURL does not contact the GPG server or the GPG server is down, the error code is not going to be added to the trusted keys list.

You can double-check whether the key has been added properly by:

$ apt-key list

You will get to see the key in the output like this:

Even now,the APT installation doesn’t know where you have to install the latest versions of MongoDB to locate the mongodb-org package.

You have two places on the APT Server where you can download and install online package sources: the sources.list file and the directory sources.list.d. The sources.list is a file listing the active APT data sources, with one source for each line. You can also add sources.list.d entries in separate files in the source.list directory.

3. Enter the following command, and create a file named mongodb-org-4.4.list in the sources.list.d directory:

$ echo "deb [ arch=amd64,arm64 ] https://repo.mongodb.org/apt/ubuntu bionic/mongodb-org/4.4 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-4.4.list

4. Upgrade your local server package index to APT to know where to find the mongodb-org package after executing this command:

$ sudo apt update

5. Now, you can install MongoDB:

$ sudo apt install mongodb-org

Press Y and then ENTER to confirm that the package is to be installed.

MongoDB is installed on the system when the command is completed. It is not ready to be used, however. Next, you're going to run MongoDB and confirm it works.

Step 2 - Running the MongoDB Service

The previous step's installation configures MongoDB to run as a daemon maintained by the system, which means you can control MongoDB using different systemctl commands. However, the service will not start automatically with this installation process.

1. To start the MongoDB service, you can use the following command:

$ sudo systemctl start mongod.service

2. Check the status of the service at this point. Systemctl will automatically attach this to any argument passed if there aren't any already, so it is not important to include it:

$ sudo systemctl status mongod

This command returns this output, which indicates that the service is running:

3. Once the service is confirmed to run as expected, start the MongoDB service:

$ sudo systemctl enable mongod

4. The database can also be verified by connecting to the database and executing a diagnostic command. The following command will show its current version, server address and port. The response of the internal MongoDB connectionStatus command will also be returned:

$ mongo --eval 'db.runCommand({ connectionStatus: 1 })'

ConnectionStatus checks back the database connection status and returns it. A value of 1 in the answer for the ok field shows that the server works as expected:

Output:Note also that a loopback address of the locally located host is running at port 27017 on 127.0.0.1. This is the default port number for MongoDB.

Next, we will examine how to manage the system instance of the MongoDB server.

Step 3 - Managing the Services

As already mentioned, mongoDB is set up as a system service for the installation process. This means that, as other Ubuntu system services, it can be managed with standard systemctl commands.

The systemctl status as previously mentioned, controls MongoDB service status:

$ sudo systemctl status mongod

To stop the service:

$ sudo systemctl stop mongod

To start the service when it is stopped:

$ sudo systemctl start mongod

To restart the server when it is running:

$ sudo systemctl restart mongod

Previously we have allowed MongoDB to start the server automatically. If this is required to be disabled, use:

$ sudo systemctl disable mongod

To re-activate the boot, execute the enable command again:

$ sudo systemctl enable mongod

Step 4 - Create MongoDB Database Root User and Password

1. MongoDB is deactivated by default, so it started off without access control. Run the following command to start the mongo shell.

$ mongo

2. You can list all available databases with the command below once you are connected to the mongo shell.

> show dbs

3. Switch first to the admin database and use the following commands to create the root user.

> use admin
> db.createUser({user:"root", pwd:"=@!#@%$admin1", roles:[{role:"root", db:"admin"}]})

4. Without the --auth command line option the mongodb instance has been started. The authentication of users' needs must be enabled by editing the /lib/systemd/system/mongod.service file.

$ sudo nano /lib/systemd/system/mongod.service

5. See the ExecStart parameter under the [Service] config section and add --auth as a new option:

ExecStart=/usr/bin/mongod --auth --config /etc/mongod.conf

Now, save the service file and exit nano:

6. Reload the systemd services:

$ sudo systemctl daemon-reload

7. Now restart mongodb and try to connect it:

$ sudo service mongod restart

8. You must now authenticate yourself as a MongoDB user when you attempt to connect to mongodb. For instance:

$ mongo -u "root" -p --authenticationDatabase "admin"

Step 5 – Creating an example MongoDB database:

1. Create a demo database:

1. We will add some data into our demo database. You can use mongo shell to interact with MongoDB instance.  

Use the following command to open the mongo shell.

$ mongo

2. After opening MongoDB prompt, create a new database with the name demoDatabase using the following command:

$ use demoDatabase

Output:Every piece of data in a MongoDB database should be part of a collection. But you don't have to explicitly create a collection. When using the insert method, the collection is automatically created.

3.Use the following command to add data into a collection:

$ db.myCollection.insert([
    {'name': 'Abhresh', 'age': 25},
   {'name': 'Ishan', 'age': 20},
    {'name': 'Nick', 'age': 30}
]);

4. After successful insertion, you will get a message like this in the prompt:

Check the database size

Backups are great if you have large databases, and you need to check the size of your database before creating a backup in order to avoid running out of storage area and thus slowing or crashing your server.  

You can use the following commands to check the size:

$ db.stats().dataSize;

Output:

Create a Backup

You have to use the -d option to create a backup of a certain database and specify the database name. In addition, you should use the -o option and indicate a path to let mongodump know where to store the backup.

Exit from the mongo shell by using CTRL + D  

Use the following commands to create a backup:  

$ mongodump -d myDatabase -o ~/backups/first_backup

If the backup is successful, you will get this message:

Please note that backup creation is very expensive and can reduce the MongoDB instance performance.

We have successfully created a backup of MongoDB database and this shows that MongoDB is perfectly working on Ubuntu system.

Uninstall MongoDB from Ubuntu

To stop MongoDB first when it is currently being executed, remove MongoDB packages using the Advanced Package Tool, the library's MongoDB databases and the MongoDB log from the log directory.

Stop MongoDB Daemon Process

$ sudo service mongod stop

Remove Packages

$ sudo apt-get purge mongodb-org*

Remove MongoDB logs

$ sudo rm -r /var/log/mongodb

The above command will remove the logs and directories.

Remove Database

We will remove the MongoDB from the var/lib/mongodb. Please check if you have MongoDb in any other location, then change the MongoDB location in the command.

$ sudo rm -r /var/lib/mongodb

Learn more about the core concepts of MongoDB administration, indexes, security, Frameworks with MongoDB Admininstration Training

Conclusion

You added the official MongoDB repository to your APT instance and installed the latest version of MongoDB in this tutorial. You then practiced some systemctl commands and tested Mongo's functionality. This article also helped you to know how to create a backup of the MongoDB database.

Abhresh

Abhresh Sugandhi

Author

Abhresh is specialized as a corporate trainer, He has a decade of experience in technical training blended with virtual webinars and instructor-led session created courses, tutorials, and articles for organizations. He is also the founder of Nikasio.com, which offers multiple services in technical training, project consulting, content development, etc.

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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 
7346
Implementing MongoDb Map Reduce using Aggregation

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