MongoDB Shell (mongosh) basics - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is mongosh in MongoDB?

mongosh is the interactive command-line shell for MongoDB. It lets you connect to your database, run commands, and see results immediately.

beginner

How do you connect to a local MongoDB server using mongosh?

Simply type mongosh in your terminal and press Enter. It connects to mongodb://localhost:27017 by default.

beginner

What command lists all databases in mongosh?

Use show dbs to see all databases on the connected MongoDB server.

beginner

How do you switch to a specific database in mongosh?

Use use <databaseName>. For example, use mydb switches to the database named mydb.

beginner

How do you insert a document into a collection using mongosh?

Use db.collectionName.insertOne({key: 'value'}). For example, db.users.insertOne({name: 'Alice', age: 25}) adds a user document.

What does the command show dbs do in mongosh?

A Connects to a new database

B Shows all collections in the current database

C Displays documents in a collection

D Lists all databases on the server

show dbs lists all databases available on the connected MongoDB server.

How do you switch to a database named shop in mongosh?

A use shop

B connect shop

C switch shop

D db shop

The command use shop switches your session to the shop database.

Which command inserts a document into the products collection?

A db.products.add({name: 'Pen'})

B db.products.insertOne({name: 'Pen'})

C insert db.products {name: 'Pen'}

D add products {name: 'Pen'}

db.products.insertOne({name: 'Pen'}) correctly inserts a single document into the products collection.

What is the default address mongosh connects to if no parameters are given?

A mongodb://localhost:27017

B mongodb://127.0.0.1:8080

C mongodb://remotehost:27017

D mongodb://localhost:3000

By default, mongosh connects to mongodb://localhost:27017.

How do you see all collections in the current database?

A db.showCollections()

B list collections

C show collections

D collections show

The command show collections lists all collections in the current database.

Explain how to connect to MongoDB using mongosh and switch to a database named testdb.

Think about starting the shell and changing the database context.

Describe the steps to insert a new document into a collection called customers using mongosh.

Focus on the insertOne method and document format.

Practice

1. What command in mongosh lists all the databases available on the server?

easy

A. show dbs

B. list databases

C. show collections

D. dbs list

Solution

1. Step 1: Understand the command purpose

   The question asks for the command that lists all databases in mongosh.

2. Step 2: Recall mongosh commands

   show dbs is the correct command to list databases. Other options are incorrect or do not exist.

3. Final Answer:

   show dbs -> Option A

4. Quick Check:

   List databases = show dbs [OK]

Hint: Use 'show dbs' to list all databases quickly [OK]

Common Mistakes:

• Confusing 'show collections' with listing databases
• Using non-existent commands like 'list databases'
• Trying 'dbs list' which is invalid

2. Which of the following is the correct syntax to switch to a database named shop in mongosh?

easy

A. switch shop

B. use shop

C. db switch shop

D. change db shop

Solution

1. Step 1: Identify the command to change database

   In mongosh, the command to switch databases is use followed by the database name.

2. Step 2: Match the correct syntax

   use shop correctly switches to the 'shop' database. Other options are invalid commands.

3. Final Answer:

   use shop -> Option B

4. Quick Check:

   Switch database = use [OK]

Hint: Remember: 'use' changes the current database [OK]

Common Mistakes:

• Using 'switch' instead of 'use'
• Adding extra words like 'db' or 'change'
• Typing commands that don't exist in mongosh

3. Given the following commands in mongosh:

use testdb
db.products.insertOne({name: 'Pen', price: 1.5})
db.products.find({name: 'Pen'}).toArray()

What will be the output of the find() command?

medium

A. [{ _id: ObjectId("...") , name: 'Pen', price: 1.5 }]

B. null

C. SyntaxError

D. []

Solution

1. Step 1: Insert a document into 'products' collection

   The insertOne() command adds a document with name 'Pen' and price 1.5 to the 'products' collection.

2. Step 2: Query the collection for documents with name 'Pen'

   The find() command searches for documents matching {name: 'Pen'}. Since we inserted one, it returns an array with that document including an auto-generated _id.

3. Final Answer:

   [{ _id: ObjectId("...") , name: 'Pen', price: 1.5 }] -> Option A

4. Quick Check:

   Inserted doc found = array with document [OK]

Hint: Inserted documents appear in find results as arrays [OK]

Common Mistakes:

• Expecting find() to return null if document exists
• Confusing syntax causing errors
• Thinking find() returns a single object, not an array

4. You run this command in mongosh:

db.users.insertOne({name: 'Alice', age: 30})

But get an error: ReferenceError: db is not defined. What is the most likely cause?

medium

A. The syntax of the insertOne command is incorrect

B. The insertOne method does not exist

C. You forgot to switch to a database using use command

D. MongoDB server is not running

Solution

1. Step 1: Understand the error message

   ReferenceError: db is not defined means the shell does not know what db is.

2. Step 2: Identify cause in mongosh context

   This usually happens if you have not selected a database with use. Without a current database, db is undefined.

3. Final Answer:

   You forgot to switch to a database using use command -> Option C

4. Quick Check:

   db undefined = forgot 'use' [OK]

Hint: Always run 'use dbname' before using db commands [OK]

Common Mistakes:

• Assuming insertOne method is missing
• Thinking syntax is wrong when it is correct
• Ignoring the need to start MongoDB server

5. You want to list all collections in the current database and then insert a document into a collection named orders. Which sequence of commands in mongosh is correct?

hard

A. show collections
use orders
db.insertOne({item: 'Book', qty: 3})

B. show dbs
db.orders.insertOne({item: 'Book', qty: 3})

C. use orders
show collections
db.insertOne({item: 'Book', qty: 3})

D. show collections
db.orders.insertOne({item: 'Book', qty: 3})

Solution

1. Step 1: List collections in current database

   show collections lists all collections in the current database. This is the first correct step.

2. Step 2: Insert document into 'orders' collection

   Use db.orders.insertOne(...) to insert a document into the 'orders' collection. This is the correct syntax.

3. Final Answer:

   show collections db.orders.insertOne({item: 'Book', qty: 3}) -> Option D

4. Quick Check:

   List collections then insert = show collections db.orders.insertOne({item: 'Book', qty: 3}) [OK]

Hint: Use 'db.collection.insertOne()' after 'show collections' [OK]

Common Mistakes:

• Trying to 'use' a collection as a database
• Calling insertOne directly on db without collection
• Listing databases instead of collections