How To Use the MongoDB Shell

The MongoDB Shell, also known as mongosh is a powerful command-line interface that allows users to interact with MongoDB databases. It provides a REPL (Read-Eval-Print Loop) environment that facilitates database management, data manipulation, and administrative tasks with ease

In this comprehensive guide, we will walk you through the process of using the MongoDB Shell, from basic commands to advanced functionality, with a full explanation of each feature.

What is the MongoDB Shell?

The MongoDB Shell (mongosh) is a JavaScript interface for interacting with MongoDB databases. It provides a command-line environment where you can execute MongoDB commands to manage your database, perform administrative tasks, and manipulate data. In short, the MongoDB Shell allows you to manage and work with your MongoDB databases directly through a flexible and powerful command-line interface.

Key features of the MongoDB Shell include:

• Interacting with MongoDB databases: Connect to and manage MongoDB instances.
• Running administrative commands: Perform tasks like managing users, roles, and collections.
• Querying and manipulating data: Use MongoDB’s powerful querying capabilities to read, write, and update data.
• Automating tasks: Execute JavaScript code within the shell to automate repetitive tasks or run scripts for bulk operations.

System Requirements for MongoDB Shell

Before you start using the MongoDB Shell, it's important to ensure that your system meets the necessary requirements for installation and operation. So let's ensure your system is ready for installation.

1. Supported Versions:

• MongoDB 4.4+ (64-bit only).

2. Compatible Operating Systems:

• Windows Server 2022
• Windows Server 2019
• Windows 11
• Linux
• macOS

3. Permissions Required:

Ensure you have the appropriate user permissions to run MongoDB services:

• Performance Monitor Users
• Performance Log Users

How to Start MongoDB Using the Shell?

Starting MongoDB using the Shell is straightforward. Below are the steps to start the MongoDB using Shell are as follows:

Step 1: Connecting to MongoDB Server

• Open your terminal (Command Prompt on Windows, or terminal on macOS/Linux).
  
• Run the following command to start the MongoDB shell:

mongosh

• This connects you to the default MongoDB instance running on localhost (127.0.0.1).
  
• If you're connecting to a remote MongoDB instance or using authentication, you can specify the URI like this:

mongosh "mongodb://<username>:<password>@<hostname>:<port>/<database>"

Step 2: Executing MongoDB Commands

Like any other command-line interface, we can enter MongoDB commands directly in the shell. Here are some essential ones:

1. Listing Databases

To list all databases on your MongoDB instance, use:

show dbs

2. Switching Databases

To switch to a specific database, use the use command followed by the database name:

use <database_name>

Example:

use admin

3. Creating Collections

To create a collection within the selected database, you can simply insert a document into a collection, and MongoDB will create it automatically. Here's an example:

db.createCollection("myCollection")

Alternatively, you can insert data directly into a non-existing collection, and it will be created:

db.myCollection.insert({ name: "MongoDB", type: "Database" })

4. Querying Data

To query data from a collection, use the find method:

db.myCollection.find({ name: "MongoDB" })

This will return all documents where the name is "MongoDB".

Advanced MongoDB Shell Commands

Once you're comfortable with the basic commands, you can explore more advanced features.

1. Running JavaScript in the MongoDB Shell

You can execute JavaScript files directly within the MongoDB Shell using the load() command. This is particularly useful for automating tasks.

load('myScript.js')

2. Creating a New Connection

You can create a new connection to another MongoDB instance using the Mongo() function:

var conn = new Mongo("mongodb://<hostname>:<port>")

This allows you to manage multiple connections to different databases.

3. Administrative Commands

The MongoDB Shell also provides commands for administrative tasks such as managing users, roles, and profiling:

Managing Users

To list users in the current database, use:

show users

To create a new user, you can use the db.createUser() function:

db.createUser({
  user: "myUser",
  pwd: "myPassword",
  roles: [ { role: "readWrite", db: "myDatabase" } ]
})

Managing Roles

To see the roles in the current database:

show roles

4. Enabling/Disabling Telemetry

MongoDB Shell provides the option to enable or disable telemetry to collect usage statistics. To enable:

enableTelemetry

To disable:

disableTelemetry

5. Clear the Shell Screen

To clear the screen in the shell, use:

cls

Getting Interactive Help from the MongoDB Shell

• The MongoDB Shell commands provide essential functionality for interacting with MongoDB databases.
  
• Commands like use and show allow us to switch databases and display information about databases and collections. exit and quit are used to exit the shell.
  
• The Mongo and connect commands are used to create new connections to MongoDB servers. The load command loads and runs JavaScript files in the shell environment.
  
• Overall, these commands streamline database management tasks and enhance the MongoDB Shell's usability.

MongoDB shell have in-built help system that we can use to get information on database system’s available commands and their syntax. The help screen can be accessed by using help command.

help

Output:

  Shell Help:

    use                                      Set current database
    show                                  'show databases'/'show dbs': Print a list of all available databases.
                                               'show collections'/'show tables': Print a list of all collections for current database.
                                               'show profile': Prints system.profile information.
                                               'show users': Print a list of all users for current database.
                                               'show roles': Print a list of all roles for current database.
                                               'show log <type>': log for current connection, if type is not set uses 'global'
                                               'show logs': Print all logs.

    exit                                       Quit the MongoDB shell with exit/exit()/.exit
    quit                                       Quit the MongoDB shell with quit/quit()
    Mongo                                      Create a new connection and return the Mongo object. Usage: new Mongo(URI, options [optional])
    connect                                    Create a new connection and return the Database object. Usage: connect(URI, username [optional], password [optional])
    it                                         result of the last line evaluated; use to further iterate
    version                                    Shell version
    load                                       Loads and runs a JavaScript file into the current shell environment
    enableTelemetry                            Enables collection of anonymous usage data to improve the mongosh CLI
    disableTelemetry                           Disables collection of anonymous usage data to improve the mongosh CLI
    passwordPrompt                             Prompts the user for a password
    sleep                                      Sleep for the specified number of milliseconds
    print                                      Prints the contents of an object to the output
    printjson                                  Alias for print()
    convertShardKeyToHashed                    Returns the hashed value for the input using the same hashing function as a hashed index.
    cls                                               Clears the screen like console.clear()
    isInteractive                              Returns whether the shell will enter or has entered interactive mode

This will display a list of available commands. To get help on a specific command, you can use:

help <command>

Example:

help show

List of Commonly Used MongoDB Shell Commands

Here is a quick reference for some commonly used MongoDB Shell commands:

• use: Switch between databases.
• show dbs: List all databases.
• show collections: List all collections in the current database.
• show users: List all users in the current database.
• show roles: List all roles in the current database.
• exit/quit: Exit the MongoDB shell.
• load(): Run a JavaScript file in the shell.
• db.<collection>.find(): Query data from a collection.
• db.createCollection(): Create a new collection.
• db.createUser(): Create a new user.

Conclusion

The MongoDB Shell is an essential tool for database administrators and developers working with MongoDB. By mastering the basic and advanced commands covered in this guide, users can perform tasks ranging from simple data manipulation to complex administrative operations.

The interactive help system within the shell makes it even easier to navigate and explore MongoDB's vast capabilities. With this knowledge, you’ll be able to interact with your MongoDB instance efficiently, whether you’re just getting started or managing large-scale databases.