$set operator for setting fields in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the $set operator do in MongoDB?

The $set operator updates the value of a field in a document. If the field does not exist, it adds the field with the specified value.

beginner

How do you use $set to change the value of a field named status to active?

You use { $set: { status: 'active' } } inside an update command to set the status field to active.

beginner

Can $set add new fields to a document if they don't exist?

Yes, $set adds the field with the given value if the field is not already in the document.

beginner

What happens if you use $set on a field that already has a value?

The existing value of the field is replaced with the new value provided in the $set operation.

intermediate

Write a MongoDB update command using $set to change the age field to 30 for documents where name is 'Alice'.

db.collection.updateMany({ name: 'Alice' }, { $set: { age: 30 } })

What does the $set operator do in MongoDB?

A Increments a numeric field by 1

B Deletes a field from a document

C Updates or adds a field with a specified value

D Replaces the entire document

$set updates the value of a field or adds it if it doesn't exist.

If you want to add a new field city with value Paris to a document, which operator do you use?

A $set

B $unset

C $push

D $inc

$set adds new fields or updates existing ones.

What happens if $set is used on a field that already exists?

A The operation fails

B The field is removed

C The field value is incremented

D The field value is replaced

$set replaces the existing field value with the new one.

Which of these is a correct use of $set to update a field score to 100?

A { $push: { score: 100 } }

B { $set: { score: 100 } }

C { $unset: { score: 100 } }

D { $inc: { score: 100 } }

$set sets the field to the specified value.

Which MongoDB command updates all documents with status 'pending' to have status 'complete'?

A db.collection.updateMany({ status: 'pending' }, { $set: { status: 'complete' } })

B db.collection.updateMany({ status: 'pending' }, { $unset: { status: 'complete' } })

C db.collection.updateMany({ status: 'complete' }, { $set: { status: 'pending' } })

D db.collection.updateMany({ status: 'pending' }, { $inc: { status: 1 } })

This command sets the status field to 'complete' for all matching documents.

Explain how the $set operator works in MongoDB updates.

Think about changing or adding information in a document.

Describe a real-life example where you would use $set in a MongoDB database.

Imagine changing details in a contact list or order system.