$nor operator behavior in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the $nor operator do in MongoDB?

The $nor operator performs a logical NOR operation on an array of query expressions. It returns documents that fail all the given conditions, meaning none of the conditions are true.

intermediate

How is $nor different from $not in MongoDB?

$nor takes an array of conditions and returns documents where none of the conditions are true. $not negates a single condition. $nor is like combining multiple $not conditions with AND logic.

beginner

Example: What documents does this query return? <br>{ $nor: [ { age: { $lt: 30 } }, { status: "A" } ] }

This query returns documents where age is NOT less than 30 AND status is NOT "A". So, only documents that fail both conditions are returned.

intermediate

Can $nor be used with a single condition array? What happens?

Yes, $nor can be used with a single condition inside an array. It returns documents where that single condition is false, effectively negating that condition.

advanced

What happens if the $nor array is empty in a query?

If the $nor array is empty, the query matches all documents because there are no conditions to fail, so none of the conditions are true by default.

What does the $nor operator return in MongoDB?

A Documents where none of the specified conditions are true

B Documents where all specified conditions are true

C Documents where at least one condition is true

D Documents where exactly one condition is true

$nor returns documents that fail all the given conditions.

Which of these is equivalent to { $nor: [ { age: { $lt: 30 } } ] }?

A { age: { $lte: 30 } }

B { age: { $gte: 30 } }

C { age: { $gt: 30 } }

D { age: { $lt: 30 } }

$nor with one condition negates it, so it matches documents where age is greater than or equal to 30.

If $nor is given an empty array, what documents are returned?

A No documents

B Only documents with null fields

C Documents with at least one true condition

D All documents

An empty $nor means no conditions to fail, so all documents match.

How does $nor combine multiple conditions?

A Returns documents where all conditions are true

B Returns documents where any condition is true

C Returns documents where all conditions are false

D Returns documents where exactly one condition is true

$nor returns documents where none of the conditions are true.

Which logical operator is $nor most similar to?

A NOT OR

B AND

C OR

D XOR

$nor means NOT (condition1 OR condition2 ...), so it is a NOT OR.

Explain how the $nor operator works in MongoDB queries.

Think about how it combines multiple conditions with NOT and OR.

Describe a real-life example where you might use $nor in a MongoDB query.

Imagine you want to exclude people younger than 30 or with status 'A'.