MongoDB Shell (mongosh) basics - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to show all databases in MongoDB shell.

MongoDB

show [1]

Drag options to blanks, or click blank then click option'

Adatabases

Bdocs

Ctables

Dcollections

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'show collections' instead of 'show databases'.

Typing 'show tables' which is not a MongoDB command.

The show databases command lists all databases in the MongoDB shell.

2fill in blank

medium

Complete the code to switch to a database named 'school'.

MongoDB

use [1]

Drag options to blanks, or click blank then click option'

Aschool

Bstudents

Cadmin

Dtest

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'use students' instead of 'use school'.

Typing 'use admin' which switches to the admin database.

The use command switches the current database. Here, we switch to the 'school' database.

3fill in blank

hard

Fix the error in the command to list collections in the current database.

MongoDB

db.[1]()

Drag options to blanks, or click blank then click option'

AshowCollections

Bcollections

ClistCollections

Dshow

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'db.showCollections()' which is not a valid method.

Using 'db.collections()' which does not exist.

The correct method to list collections in the current database is db.getCollectionNames() or db.listCollections().

4fill in blank

hard

Fill both blanks to insert a document with name 'Alice' and age 25 into the 'users' collection.

MongoDB

db.users.[1]([2])

Drag options to blanks, or click blank then click option'

AinsertOne

B{ name: 'Alice', age: 25 }

C{ name: 'Bob', age: 30 }

DinsertMany

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'insertMany' when inserting only one document.

Inserting the wrong document data.

Use insertOne to add a single document. The document is an object with name and age fields.

5fill in blank

hard

Fill all three blanks to find all documents in 'products' collection where price is greater than 100.

MongoDB

db.products.[1]([2]: { [3]: 100 })

Drag options to blanks, or click blank then click option'

Afind

Bprice

C$gt

DinsertOne

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'insertOne' instead of 'find'.

Using wrong operator like '$lt' instead of '$gt'.

The find method retrieves documents. The query uses price field with $gt operator for 'greater than'.

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