$mul operator for multiplication in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the $mul operator do in MongoDB?

The $mul operator multiplies the value of a field by a specified number and updates the field with the new value.

beginner

How do you use $mul in an update query?

You use the $mul update operator to multiply a field's value. For example: { $mul: { fieldName: 2 } } doubles the value of fieldName.

intermediate

Can $mul be used to multiply by decimal numbers?

Yes, $mul can multiply a field by any numeric value, including decimals (floats).

intermediate

What happens if the field used with $mul does not exist in the document?

If the field does not exist, MongoDB will not create it or perform multiplication. The update will not change that document.

beginner

Write a MongoDB update query using $mul to triple the value of the field price in documents where category is 'books'.

db.collection.updateMany({ category: 'books' }, { $mul: { price: 3 } })

What does the $mul operator do in MongoDB?

A Multiplies a field's value by a number

B Adds a number to a field's value

C Deletes a field from a document

D Creates a new field with a value

$mul multiplies the value of a field by a specified number.

If you want to double the value of a field score, which update operator would you use?

A { $set: { score: 2 } }

B { $inc: { score: 2 } }

C { $mul: { score: 2 } }

D { $push: { score: 2 } }

$mul multiplies the field value; doubling means multiplying by 2.

What happens if the field you want to multiply with $mul does not exist?

A MongoDB does not change the document

B MongoDB creates the field and sets it to the multiplier

C MongoDB creates the field and sets it to zero

D MongoDB throws an error

MongoDB does not create the field or change the document if the field is missing.

Can $mul multiply a field by a decimal number?

A No

B Yes

C Only if the field is an integer

D Only if the field is a string

$mul works with any numeric value, including decimals.

Which MongoDB method is commonly used with $mul to update multiple documents?

A deleteMany()

B find()

C insertOne()

D updateMany()

updateMany() updates multiple documents and can use $mul.

Explain how the $mul operator works in MongoDB and give an example of its use.

Think about how you would increase a price by multiplying it.

What happens if you try to use $mul on a field that does not exist in a document?

Consider how MongoDB handles missing fields in updates.