$nin for not in set in MongoDB - Step-by-Step Execution

Concept Flow - $nin for not in set

Start Query

↓

Check each document's field

↓

Is field value NOT in $nin array?

No→Exclude document

Yes↓

Include document in result

↓

Repeat for all documents

↓

Return filtered documents

The query checks each document's field value and includes it only if the value is NOT in the given $nin array.

Execution Sample

MongoDB

db.collection.find({ age: { $nin: [20, 30, 40] } })

Finds documents where the age is NOT 20, 30, or 40.

Execution Table

Step	Document	Field Value (age)	Check $nin Condition	Include in Result?
1	{_id:1, age:25}	25	25 NOT in [20,30,40] -> True	Yes
2	{_id:2, age:30}	30	30 NOT in [20,30,40] -> False	No
3	{_id:3, age:35}	35	35 NOT in [20,30,40] -> True	Yes
4	{_id:4, age:40}	40	40 NOT in [20,30,40] -> False	No
5	{_id:5, age:50}	50	50 NOT in [20,30,40] -> True	Yes
6	All documents checked	-	-	Query ends

💡 All documents checked; only those with age NOT in [20,30,40] included.

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5	Final
Current Document	None	{_id:1, age:25}	{_id:2, age:30}	{_id:3, age:35}	{_id:4, age:40}	{_id:5, age:50}	None
Included in Result	No	Yes	No	Yes	No	Yes	Yes documents: {_id:1,3,5}

Key Moments - 2 Insights

Why is the document with age 30 excluded even though 30 is a number?

Because $nin means 'NOT in' the given array. Since 30 is in [20,30,40], it fails the condition and is excluded (see execution_table step 2).

What happens if the field is missing in a document?

Documents missing the field are included because their field value is considered undefined, which is not in the $nin array (not shown in this example but important to know).

Visual Quiz - 3 Questions

Look at the execution table, which document is included at step 3?

A {_id:4, age:40}

B {_id:3, age:35}

C {_id:2, age:30}

D {_id:5, age:50}

💡 Hint

Check the 'Include in Result?' column at step 3 in the execution_table.

At which step does the condition become false?

A Step 3

B Step 1

C Step 2

D Step 5

💡 Hint

Look for 'False' in the 'Check $nin Condition' column in the execution_table.

If we add 50 to the $nin array, what happens to the document at step 5?

A It is excluded from the result

B It is included in the result

C It causes an error

D It is included only if age is 50

💡 Hint

Refer to how $nin excludes values present in its array, as shown in the execution_table.

Concept Snapshot

$nin operator filters documents where the field's value is NOT in the specified array.
Syntax: { field: { $nin: [value1, value2, ...] } }
Includes documents with field values outside the array.
Missing fields are included by default.
Useful to exclude multiple values in one query.

Full Transcript

This visual execution shows how MongoDB's $nin operator works. The query checks each document's field value against an array of excluded values. If the value is NOT in the array, the document is included in the result. For example, with $nin: [20,30,40], documents with age 25, 35, and 50 are included, while those with 30 and 40 are excluded. The execution table traces each document step-by-step, showing the condition check and inclusion decision. Key points include understanding that $nin excludes values inside the array and includes missing fields. The quiz reinforces these ideas by asking about specific steps and changes to the $nin array.