Database and collection creation in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

How do you create a new database in MongoDB?

In MongoDB, you create a new database by switching to it using use databaseName. The database is created when you first store data in it.

beginner

What command creates a new collection explicitly in MongoDB?

Use db.createCollection('collectionName') to create a new collection explicitly.

beginner

True or False: In MongoDB, a database is created immediately when you switch to it with use.

False. The database is created only when you insert the first document into a collection within that database.

beginner

What happens if you insert a document into a collection that does not exist in MongoDB?

MongoDB automatically creates the collection and the database (if not existing) when you insert the first document.

intermediate

Explain the difference between creating a collection explicitly and implicitly in MongoDB.

Explicit creation uses db.createCollection(). Implicit creation happens automatically when you insert a document into a non-existing collection.

Which command switches to a database named 'shop' in MongoDB?

A use shop

B db.shop()

C create database shop

D switch shop

The use shop command switches to the 'shop' database.

How do you explicitly create a collection named 'products'?

A db.products.insert()

B use products

C create collection products

D db.createCollection('products')

Use db.createCollection('products') to explicitly create a collection.

When is a MongoDB database actually created?

A When you run <code>use</code> command

B When you create a collection explicitly

C When you insert the first document

D When you start the MongoDB server

The database is created when the first document is inserted into a collection.

What happens if you insert a document into a non-existing collection?

A Collection and database are created automatically

B Error is thrown

C Nothing happens

D You must create collection first

MongoDB creates the collection and database automatically on first insert.

Which of these is NOT a way to create a collection in MongoDB?

A Using db.createCollection()

B Using SQL CREATE TABLE command

C Inserting a document into a new collection

D Switching to a new database with use command

SQL commands like CREATE TABLE do not work in MongoDB.

Describe the process of creating a new database and collection in MongoDB.

Think about what happens when you insert data.

Explain the difference between implicit and explicit collection creation in MongoDB.

One is manual, the other automatic.

Practice

1. What does the command use myDatabase do in MongoDB?

easy

A. It deletes the database named 'myDatabase'.

B. It creates a collection named 'myDatabase'.

C. It switches to the database named 'myDatabase' or creates it if it doesn't exist.

D. It lists all collections in the current database.

Solution

1. Step 1: Understand the use command

   The use command in MongoDB switches the current database context to the specified database.

2. Step 2: Behavior when database does not exist

   If the specified database does not exist, MongoDB creates it when you first store data in it.

3. Final Answer:

   It switches to the database named 'myDatabase' or creates it if it doesn't exist. -> Option C

4. Quick Check:

   use databaseName switches or creates database [OK]

Hint: Remember: use switches or creates database [OK]

Common Mistakes:

• Thinking use creates collections
• Confusing database and collection commands
• Assuming use deletes databases

2. Which of the following is the correct syntax to create a new collection named users in the current database?

easy

A. db.createCollection('users')

B. create collection users

C. db.users.create()

D. use users

Solution

1. Step 1: Identify the MongoDB command for collection creation

   The correct MongoDB command to create a collection is db.createCollection('collectionName').

2. Step 2: Match the syntax with the options

   db.createCollection('users') matches the correct syntax exactly for creating a collection named 'users'.

3. Final Answer:

   db.createCollection('users') -> Option A

4. Quick Check:

   Use db.createCollection('name') to create collections [OK]

Hint: Use db.createCollection('name') to create collections [OK]

Common Mistakes:

• Using SQL-like syntax such as 'create collection users'
• Trying to create collection with db.users.create()
• Using use users to create collection

3. What will be the result of running these commands in order?

use shopDB
db.createCollection('products')
db.getCollectionNames()

medium

A. Error: createCollection not found

B. ['shopDB']

C. []

D. ['products']

Solution

1. Step 1: Switch to or create the database 'shopDB'

   The use shopDB command switches to the database named 'shopDB'. If it doesn't exist, it will be created when data is added.

2. Step 2: Create a collection named 'products'

   The command db.createCollection('products') creates a new collection called 'products' inside 'shopDB'.

3. Step 3: List collections in the current database

   db.getCollectionNames() returns an array of collection names in the current database. Since 'products' was created, it returns ['products'].

4. Final Answer:

   ['products'] -> Option D

5. Quick Check:

   Created collection appears in db.getCollectionNames() [OK]

Hint: Created collections appear in db.getCollectionNames() [OK]

Common Mistakes:

• Expecting database name in collection list
• Assuming collections list is empty after creation
• Confusing collection names with database names

4. Identify the error in this MongoDB command sequence:

use testDB
db.createCollection(users)

medium

A. Missing quotes around collection name 'users'.

B. The use command is incorrect.

C. The collection name cannot be 'users'.

D. The command createCollection does not exist.

Solution

1. Step 1: Check syntax of createCollection command

   The collection name must be a string, so it requires quotes around it.

2. Step 2: Identify the error in the command

   The command db.createCollection(users) is missing quotes around 'users', causing a syntax error.

3. Final Answer:

   Missing quotes around collection name 'users'. -> Option A

4. Quick Check:

   Collection names must be strings in quotes [OK]

Hint: Always put collection names in quotes in createCollection [OK]

Common Mistakes:

• Omitting quotes around collection names
• Misusing use command syntax
• Thinking collection names cannot be common words

5. You want to create a new database called libraryDB and inside it a collection named books. Which sequence of commands will achieve this correctly?

hard

A. create database libraryDB
create collection books

B. use libraryDB
db.createCollection('books')

C. use books
db.createCollection('libraryDB')

D. db.createCollection('libraryDB.books')

Solution

1. Step 1: Switch to or create the database 'libraryDB'

   The command use libraryDB switches to the database named 'libraryDB'. If it doesn't exist, it will be created when data is added.

2. Step 2: Create the collection 'books' inside 'libraryDB'

   Using db.createCollection('books') creates the collection named 'books' in the current database context.

3. Final Answer:

   use libraryDB db.createCollection('books') -> Option B

4. Quick Check:

   Switch database then create collection [OK]

Hint: Switch database first, then create collection inside it [OK]

Common Mistakes:

• Trying to create database and collection in one command
• Using SQL syntax like 'create database'
• Confusing collection and database names