$nin for not in set in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the $nin operator do in MongoDB?

The $nin operator selects documents where the value of a field is not in the specified array of values.

beginner

How would you find documents where the field color is not 'red', 'blue', or 'green' using $nin?

{ color: { $nin: ['red', 'blue', 'green'] } }

This query returns documents where color is any value except 'red', 'blue', or 'green'.

intermediate

Can $nin be used with fields that contain arrays?

Yes, $nin checks if none of the values in the field's array are in the specified array. If any value matches, the document is excluded.

intermediate

What happens if you use $nin with an empty array like { field: { $nin: [] } }?

The query matches all documents because no values are excluded.

beginner

Is $nin the opposite of $in?

Yes, $nin selects documents where the field's value is not in the given array, while $in selects documents where the field's value is in the array.

Which MongoDB operator selects documents where a field's value is NOT in a list of values?

A $nin

B $in

C $eq

D $ne

$nin selects documents where the field's value is not in the specified array.

What will the query { age: { $nin: [20, 30, 40] } } return?

A Documents where age is 20, 30, or 40

B Documents where age is not 20, 30, or 40

C Documents where age is exactly 20

D Documents where age is missing

The query returns documents where age is not any of the values 20, 30, or 40.

If a field contains an array, how does $nin behave?

A Matches if any element is in the array

B Matches if all elements are in the array

C Matches if none of the elements are in the array

D Does not work with arrays

$nin matches documents where none of the array elements are in the specified list.

What does { field: { $nin: [] } } match?

A No documents

B All documents

C Documents where field is null

D Documents where field is an empty array

An empty array means no values are excluded, so all documents match.

Which operator is the direct opposite of $nin?

A $ne

B $in

C $eq

D $exists

$in selects documents where the field's value is in the array, opposite of $nin.

Explain how the $nin operator works in MongoDB queries.

Think about how you exclude certain items from a list.

Describe a real-life example where you might use $nin in a database query.

Imagine you want to find all fruits except apples and bananas.