$nin for not in set in MongoDB

Introduction

Use $nin to find items that do NOT match any value in a list. It helps exclude unwanted data.

You want to find all products except those in certain categories.

You need to get users who are not from specific cities.

You want to exclude certain tags from search results.

You want to filter out orders that have specific statuses.

You want to find documents where a field's value is not in a given set.

Syntax

MongoDB

{ field: { $nin: [value1, value2, ...] } }

The $nin operator takes an array of values to exclude.

It matches documents where the field's value is not in the given array.

Examples

Finds documents where category is NOT 'electronics' or 'furniture'.

MongoDB

{ category: { $nin: ['electronics', 'furniture'] } }

Finds documents where age is not 20, 30, or 40.

MongoDB

{ age: { $nin: [20, 30, 40] } }

Finds documents where status is neither 'pending' nor 'cancelled'.

MongoDB

{ status: { $nin: ['pending', 'cancelled'] } }

Sample Program

This query finds all orders where the status is NOT 'shipped' or 'delivered'.

MongoDB

db.orders.find({ status: { $nin: ['shipped', 'delivered'] } })

Important Notes

If the field does not exist in a document, that document will be included because its value is not in the list.

$nin is the opposite of $in, which finds values inside the list.

Summary

$nin helps exclude documents with certain values.

Use it when you want to filter out unwanted data from your results.

It works by matching documents where the field's value is NOT in the given array.

Practice

1. What does the MongoDB operator $nin do in a query?

easy

A. Selects documents where the field's value is in the specified array

B. Selects documents where the field's value is NOT in the specified array

C. Updates documents with values in the specified array

D. Deletes documents where the field's value is in the specified array

Solution

1. Step 1: Understand the purpose of $nin

   The $nin operator is used to filter documents where a field's value is NOT included in a given list of values.

2. Step 2: Compare with other operators

   Unlike $in which selects values inside the array, $nin excludes those values.

3. Final Answer:

   Selects documents where the field's value is NOT in the specified array -> Option B

4. Quick Check:

   $nin excludes values = B [OK]

Hint: Remember: $nin means NOT in list [OK]

Common Mistakes:

• Confusing $nin with $in
• Thinking it updates or deletes documents
• Using it to select values inside the array

2. Which of the following is the correct syntax to find documents where the field status is NOT 'active' or 'pending' using $nin?

easy

A. { status: { $nin: ['active', 'pending'] } }

B. { status: { $nin: 'active', 'pending' } }

C. { status: { $nin: ['active'] || ['pending'] } }

D. { status: { $nin: 'active' && 'pending' } }

Solution

1. Step 1: Check the correct $nin syntax

   The $nin operator requires an array of values inside square brackets to specify the excluded set.

2. Step 2: Validate each option

   { status: { $nin: ['active', 'pending'] } } correctly uses an array with two strings. Options B, C, and D have syntax errors or invalid expressions.

3. Final Answer:

   { status: { $nin: ['active', 'pending'] } } -> Option A

4. Quick Check:

   Correct array syntax for $nin = A [OK]

Hint: Use square brackets for arrays in $nin [OK]

Common Mistakes:

• Using multiple arguments instead of an array
• Using logical operators inside $nin
• Missing square brackets around values

3. Given the collection products with documents:

{ name: 'Pen', category: 'stationery' }

{ name: 'Apple', category: 'fruit' }

{ name: 'Notebook', category: 'stationery' }

{ name: 'Carrot', category: 'vegetable' }

What will be the result of this query?

db.products.find({ category: { $nin: ['fruit', 'vegetable'] } })

medium

A. All documents returned

B. [{ name: 'Apple', category: 'fruit' }, { name: 'Carrot', category: 'vegetable' }]

C. [] (empty array)

D. [{ name: 'Pen', category: 'stationery' }, { name: 'Notebook', category: 'stationery' }]

Solution

1. Step 1: Understand the $nin filter

   The query excludes documents where category is 'fruit' or 'vegetable'.

2. Step 2: Identify matching documents

   Documents with category 'stationery' are not in ['fruit', 'vegetable'], so they match. 'Pen' and 'Notebook' have 'stationery'.

3. Final Answer:

   [{ name: 'Pen', category: 'stationery' }, { name: 'Notebook', category: 'stationery' }] -> Option D

4. Quick Check:

   Exclude 'fruit' and 'vegetable' = stationery items only [OK]

Hint: Exclude unwanted categories with $nin array [OK]

Common Mistakes:

• Confusing $nin with $in
• Expecting documents with excluded categories
• Assuming empty result when some match

4. You wrote this query to exclude users with roles 'admin' or 'moderator':

db.users.find({ role: { $nin: 'admin', 'moderator' } })

But it throws an error. What is the problem?

medium

A. The $nin operator requires an array, not multiple arguments

B. The field name role is misspelled

C. The query should use $in instead of $nin

D. MongoDB does not support $nin operator

Solution

1. Step 1: Check $nin syntax

   $nin expects a single array argument listing values to exclude.

2. Step 2: Identify the error in the query

   The query passes two separate string arguments instead of one array, causing syntax error.

3. Final Answer:

   The $nin operator requires an array, not multiple arguments -> Option A

4. Quick Check:

   $nin needs array input = C [OK]

Hint: Always wrap values in an array for $nin [OK]

Common Mistakes:

• Passing multiple arguments instead of an array
• Using wrong operator $in by mistake
• Assuming $nin is unsupported

5. You have a collection orders with documents:

{ orderId: 1, status: 'shipped' }

{ orderId: 2, status: 'pending' }

{ orderId: 3, status: 'cancelled' }

{ orderId: 4, status: 'delivered' }

You want to find orders NOT in statuses 'pending' or 'cancelled' AND exclude orders with orderId 4. Which query correctly uses $nin to achieve this?

hard

A. { status: { $nin: ['pending', 'cancelled'] }, orderId: { $ne: 4 } }

B. { status: { $nin: ['pending', 'cancelled', 4] } }

C. { status: { $nin: ['pending', 'cancelled'] }, orderId: { $nin: [4] } }

D. { status: { $nin: ['pending', 'cancelled'] }, orderId: { $in: [4] } }

Solution

1. Step 1: Exclude statuses 'pending' and 'cancelled'

   Use { status: { $nin: ['pending', 'cancelled'] } } to exclude these statuses.

2. Step 2: Exclude orderId 4 using $nin

   Use { orderId: { $nin: [4] } } to exclude orderId 4 as well.

3. Step 3: Combine conditions

   Both conditions together filter out unwanted statuses and orderId 4.

4. Final Answer:

   { status: { $nin: ['pending', 'cancelled'] }, orderId: { $nin: [4] } } -> Option C

5. Quick Check:

   Use $nin on both fields = A [OK]

Hint: Use separate $nin for each field to exclude multiple sets [OK]

Common Mistakes:

• Putting orderId inside status array
• Using $ne instead of $nin for multiple values
• Using $in to exclude values