findOne method in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the findOne method do in MongoDB?

The findOne method searches a collection and returns the first document that matches the query criteria. If no document matches, it returns null.

beginner

How do you use findOne to find a user with the name 'Alice'?

You call db.collection.findOne({ name: 'Alice' }). This returns the first document where the name field equals 'Alice'.

intermediate

What is the difference between findOne and find in MongoDB?

findOne returns a single document (the first match), while find returns a cursor to all matching documents.

beginner

What does findOne return if no documents match the query?

It returns null, meaning no matching document was found.

intermediate

Can you use projection with findOne? What does it do?

Yes, you can pass a projection object as the second argument to findOne. It controls which fields are included or excluded in the returned document.

What does findOne return if multiple documents match the query?

A Null

B All matching documents

C An error

D The first matching document

findOne returns only the first document that matches the query.

How do you exclude the password field from the result using findOne?

A db.collection.findOne({}, { projection: { password: 0 } })

B db.collection.findOne({}, { password: 1 })

C db.collection.findOne({ password: 0 })

D db.collection.findOne({ password: 1 })

Use projection with { password: 0 } to exclude the password field.

Which of these is a valid findOne query to find a document with age greater than 25?

A db.collection.findOne({ age: > 25 })

B db.collection.findOne({ age: { $gt: 25 } })

C db.collection.findOne({ age: gt 25 })

D db.collection.findOne({ age: { > 25 } })

MongoDB uses $gt operator inside an object to specify 'greater than'.

If no document matches the query, what does findOne return?

A An empty object {}

B An error

C Null

D Undefined

findOne returns null when no match is found.

Which method would you use to get multiple documents matching a query?

A find

B findMany

C getAll

D findOne

find returns a cursor to all matching documents.

Explain how to use the findOne method to retrieve a document by a specific field value.

Think about searching for a user by name.

Describe how to use projection with findOne and why it might be useful.

Consider hiding a password field in the result.