$nor operator behavior in MongoDB - Step-by-Step Execution

Concept Flow - $nor operator behavior

Start with $nor query

↓

Evaluate each condition inside $nor

↓

Are ALL conditions false?

No→Document excluded

Yes↓

Document included in result

The $nor operator checks multiple conditions and returns documents only if all those conditions are false.

Execution Sample

MongoDB

db.collection.find({ $nor: [ { age: { $lt: 30 } }, { city: 'NY' } ] })

Find documents where age is NOT less than 30 AND city is NOT 'NY'.

Execution Table

Step	Document	Condition 1 (age < 30)	Condition 2 (city = 'NY')	All conditions false?	Include Document?
1	{ age: 25, city: 'LA' }	True	False	No	No
2	{ age: 35, city: 'NY' }	False	True	No	No
3	{ age: 40, city: 'LA' }	False	False	Yes	Yes
4	{ age: 28, city: 'NY' }	True	True	No	No
5	{ age: 50, city: 'SF' }	False	False	Yes	Yes
6	End of documents				Query ends

💡 Query ends after checking all documents; only those with all conditions false are included.

Variable Tracker

Document	Condition 1 (age < 30)	Condition 2 (city = 'NY')	All conditions false?	Included
{ age: 25, city: 'LA' }	True	False	No	No
{ age: 35, city: 'NY' }	False	True	No	No
{ age: 40, city: 'LA' }	False	False	Yes	Yes
{ age: 28, city: 'NY' }	True	True	No	No
{ age: 50, city: 'SF' }	False	False	Yes	Yes

Key Moments - 2 Insights

Why does a document get excluded if only one condition inside $nor is true?

Because $nor requires ALL conditions to be false to include the document. If even one condition is true, the document is excluded, as shown in rows 1 and 2 of the execution_table.

Is $nor the same as negating $or?

Yes, $nor returns documents where none of the $or conditions are true. This means all conditions inside $nor must be false, as demonstrated in the execution_table where documents with any true condition are excluded.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'All conditions false?' for the document { age: 40, city: 'LA' }?

A True

B Yes

C No

D False

💡 Hint

Check the row where Document is { age: 40, city: 'LA' } in the execution_table under 'All conditions false?' column.

At which step does the query include the document in the result?

A Step 3

B Step 1

C Step 2

D Step 4

💡 Hint

Look for the row where 'Include Document?' is 'Yes' in the execution_table.

If the condition { city: 'NY' } was removed from $nor, how would the inclusion of documents change?

A All documents would be included

B No documents would be included

C Only documents with age >= 30 would be included

D Only documents with city 'NY' would be included

💡 Hint

Removing one condition means only the remaining condition affects inclusion; check how condition 1 affects inclusion in variable_tracker.

Concept Snapshot

$nor operator:
- Takes an array of conditions.
- Returns documents where ALL conditions are false.
- Equivalent to NOT (condition1 OR condition2 ...).
- Useful to exclude multiple conditions at once.
- Syntax: { $nor: [ {cond1}, {cond2}, ... ] }

Full Transcript

The $nor operator in MongoDB is used to find documents where none of the specified conditions are true. It evaluates each condition inside its array and includes only those documents where all conditions are false. For example, if you query with $nor: [ { age: { $lt: 30 } }, { city: 'NY' } ], it returns documents where age is not less than 30 and city is not 'NY'. The execution table shows step-by-step how each document is checked against the conditions, and only those with all false conditions are included. This operator is like negating an OR condition, so if any condition is true, the document is excluded. Understanding this helps avoid confusion about why some documents are included or excluded in query results.