Database and collection creation in MongoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this MongoDB command?

Consider the following MongoDB shell command:

use myNewDB

What will be the output after running this command?

MongoDB

use myNewDB

A "database myNewDB dropped"

B "error: database does not exist"

C "switched to db myNewDB"

D "created database myNewDB"

💡 Hint

The 'use' command switches the current database context.

The 'use' command in MongoDB switches the shell to the specified database. If the database does not exist yet, it will be created when you first store data in it. The shell outputs 'switched to db '.

❓ query_result

intermediate

What happens when you create a collection explicitly?

Given the command:

db.createCollection('users')

What is the result of running this command in MongoDB shell?

MongoDB

db.createCollection('users')

A {"ok": 1}

B {"ok": 0}

C null

D Error: collection already exists

💡 Hint

Creating a collection explicitly returns a success status.

The createCollection command returns an object with 'ok' set to 1 on success. If the collection already exists, it throws an error.

📝 Syntax

advanced

Which command correctly creates a capped collection named 'logs'?

You want to create a capped collection named 'logs' with a maximum size of 1MB. Which command is correct?

A db.createCollection('logs', {size: 1048576, capped: false})

B db.createCollection('logs', {capped: true, size: 1048576})

C db.createCollection('logs', {capped: true, max: 1048576})

D db.createCollection('logs', {maxSize: 1048576, capped: true})

💡 Hint

The 'capped' option must be true and 'size' specifies the max bytes.

To create a capped collection, set 'capped' to true and specify 'size' in bytes. 'max' is for max documents, not size. 'maxSize' is not a valid option.

🧠 Conceptual

advanced

Why does MongoDB create a database only after inserting data?

In MongoDB, when you run use newDB, the database is not created immediately. Why is this behavior designed this way?

A Because databases are created automatically when the server starts.

B Because the 'use' command is only for switching databases and cannot create them.

C Because MongoDB requires a restart to create new databases.

D Because MongoDB creates databases lazily only when data is stored to save disk space.

💡 Hint

Think about resource usage and efficiency.

MongoDB delays creating a database until data is inserted to avoid creating empty databases and wasting disk space.

🔧 Debug

expert

Identify the error in this collection creation command

What error will this command produce?

db.createCollection('events', {capped: true, size: '1000'})

Note: size is given as a string.

MongoDB

db.createCollection('events', {capped: true, size: '1000'})

A MongoServerError: capped collections require size in bytes

B SyntaxError: unexpected string

C No error, collection created successfully

D TypeError: size must be a number

💡 Hint

Check the data type required for the size option.

The 'size' option must be a number representing bytes. Passing a string causes a MongoServerError indicating the size must be numeric.