$nor operator behavior in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to find documents where neither condition is true using $nor.

MongoDB

db.collection.find({ $nor: [ [1] ] })

Drag options to blanks, or click blank then click option'

A{ age: { $lt: 30 } }

B{ age: { $gt: 30 } }

C{ age: 30 }

D{ age: { $eq: 30 } }

Attempts:

3 left

💡 Hint

Common Mistakes

Using $nor with a single condition that is true instead of false.

Confusing $nor with $or.

The $nor operator takes an array of conditions and matches documents that fail all of them. Here, it matches documents where age is not less than 30.

2fill in blank

medium

Complete the code to find documents where neither age is less than 25 nor status is 'A'.

MongoDB

db.collection.find({ $nor: [ [1] ] })

Drag options to blanks, or click blank then click option'

A[ { age: { $lt: 25 } }, { status: 'A' } ]

B{ age: { $lt: 25 }, status: 'A' }

C{ age: { $lt: 25 } }, { status: 'A' }

D{ age: { $lt: 25 }, status: { $ne: 'A' } }

Attempts:

3 left

💡 Hint

Common Mistakes

Putting multiple conditions inside one object instead of separate objects in the array.

Not using an array for $nor.

The $nor operator expects an array of conditions. Each condition is an object. Here, the array has two objects: one for age less than 25, and one for status equal to 'A'.

3fill in blank

hard

Fix the error in the query to correctly use $nor with two conditions.

MongoDB

db.collection.find({ $nor: [1] })

Drag options to blanks, or click blank then click option'

A{ age: { $lt: 20 }, status: 'B' }

B[ { age: { $lt: 20 }, status: 'B' } ]

C{ age: { $lt: 20 } }, { status: 'B' }

D[ { age: { $lt: 20 } }, { status: 'B' } ]

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a single object with multiple conditions instead of an array.

Passing multiple objects separated by commas without an array.

$nor requires an array of condition objects. Option D correctly provides an array with two separate condition objects.

4fill in blank

hard

Fill both blanks to find documents where neither age is greater than 40 nor status is 'C'.

MongoDB

db.collection.find({ $nor: [ [1], [2] ] })

Drag options to blanks, or click blank then click option'

A{ age: { $gt: 40 } }

B{ age: { $lt: 40 } }

C{ status: 'C' }

D{ status: 'B' }

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up greater than and less than operators.

Using wrong status values.

The $nor operator takes an array of conditions. Here, the conditions are age greater than 40 and status equal to 'C'. Documents matching neither condition are returned.

5fill in blank

hard

Fill all three blanks to find documents where none of these are true: age less than 18, status 'D', or score greater than 90.

MongoDB

db.collection.find({ $nor: [ [1], [2], [3] ] })

Drag options to blanks, or click blank then click option'

A{ age: { $lt: 18 } }

B{ status: 'D' }

C{ score: { $gt: 90 } }

D{ score: { $lt: 90 } }

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong comparison operators for score.

Not separating conditions into individual objects.

The $nor operator matches documents where none of the listed conditions are true. Here, it excludes documents with age less than 18, status 'D', or score greater than 90.

Practice

1. What does the $nor operator do in MongoDB queries?

easy

A. Finds documents where all specified conditions are true

B. Finds documents where at least one condition is true

C. Finds documents where none of the specified conditions are true

D. Finds documents that match exactly one condition

Solution

1. Step 1: Understand the purpose of $nor

   The $nor operator returns documents that do not satisfy any of the given conditions.

2. Step 2: Compare with other logical operators

   Unlike $and or $or, $nor excludes documents matching any condition in its array.

3. Final Answer:

   Finds documents where none of the specified conditions are true -> Option C

4. Quick Check:

   $nor excludes all matching conditions = B [OK]

Hint: Think: no conditions should be true for $nor [OK]

Common Mistakes:

• Confusing $nor with $or
• Assuming it returns documents matching any condition
• Thinking it requires all conditions to be true

2. Which of the following is the correct syntax to use $nor in a MongoDB query to exclude documents where age is 25 or status is "active"?

easy

A. { $nor: { $or: [ { age: 25 }, { status: "active" } ] } }

B. { $nor: { age: 25, status: "active" } }

C. { $nor: [ age: 25, status: "active" ] }

D. { $nor: [ { age: 25 }, { status: "active" } ] }

Solution

1. Step 1: Recall $nor syntax

   $nor requires an array of condition objects inside square brackets.

2. Step 2: Check each option's structure

   { $nor: [ { age: 25 }, { status: "active" } ] } correctly uses an array of conditions. Options B and D use objects incorrectly, and C has invalid array syntax.

3. Final Answer:

   { $nor: [ { age: 25 }, { status: "active" } ] } -> Option D

4. Quick Check:

   Array of conditions inside $nor = A [OK]

Hint: Use square brackets for conditions array in $nor [OK]

Common Mistakes:

• Using curly braces instead of square brackets for conditions
• Passing a single object instead of an array
• Nesting $or inside $nor unnecessarily

3. Given the collection documents:

[{ "name": "Alice", "age": 30, "status": "active" }, { "name": "Bob", "age": 25, "status": "inactive" }, { "name": "Carol", "age": 35, "status": "active" }]

What will be the result of this query?

{ $nor: [ { age: 25 }, { status: "active" } ] }

medium

A. [] (empty array)

B. [{ "name": "Bob", "age": 25, "status": "inactive" }]

C. [{ "name": "Bob", "age": 25, "status": "inactive" }, { "name": "Carol", "age": 35, "status": "active" }]

D. [{ "name": "Bob", "age": 25, "status": "inactive" }, { "name": "Alice", "age": 30, "status": "active" }]

Solution

1. Step 1: Understand the $nor conditions

   The query excludes documents where age is 25 OR status is "active".

2. Step 2: Check each document against conditions

   Alice: status "active" -> excluded; Bob: age 25 -> excluded; Carol: status "active" -> excluded.

3. Final Answer:

   [] (empty array) -> Option A

4. Quick Check:

   All documents match at least one condition, so none returned = A [OK]

Hint: Exclude any document matching any condition in $nor [OK]

Common Mistakes:

• Returning documents that match one condition
• Confusing $nor with $or
• Assuming some documents pass when all match conditions

4. You wrote this MongoDB query but it throws an error:

{ $nor: { age: { $gt: 30 }, status: "inactive" } }

What is the problem and how to fix it?

medium

A. The field names must be strings; fix: { $nor: [ { "age": { $gt: 30 } }, { "status": "inactive" } ] }

B. The conditions must be inside an array; fix: { $nor: [ { age: { $gt: 30 } }, { status: "inactive" } ] }

C. The operator $gt is invalid; fix: use $gte instead

D. The query must use $and instead of $nor

Solution

1. Step 1: Identify the syntax error

   $nor expects an array of condition objects, but here it has a single object.

2. Step 2: Correct the syntax

   Wrap each condition inside its own object within an array to fix the error.

3. Final Answer:

   The conditions must be inside an array; fix: { $nor: [ { age: { $gt: 30 } }, { status: "inactive" } ] } -> Option B

4. Quick Check:

   $nor needs array of conditions = C [OK]

Hint: Always use an array of conditions with $nor [OK]

Common Mistakes:

• Passing a single object instead of an array
• Misusing comparison operators
• Confusing $nor with $and

5. You have a collection with documents:

[{ "item": "pen", "qty": 10, "status": "A" }, { "item": "pencil", "qty": 5, "status": "D" }, { "item": "notebook", "qty": 15, "status": "A" }, { "item": "eraser", "qty": 0, "status": "D" }]

Write a $nor query to find documents where qty is not 0 and status is not "D". Which query returns the correct documents?

hard

A. { $nor: [ { qty: 0 }, { status: "D" } ] }

B. { $nor: [ { qty: { $ne: 0 } }, { status: { $ne: "D" } } ] }

C. { $nor: [ { qty: { $eq: 0 } }, { status: { $ne: "D" } } ] }

D. { $nor: [ { qty: { $gt: 0 } }, { status: { $ne: "D" } } ] }

Solution

1. Step 1: Understand the requirement

   We want documents where qty is NOT 0 and status is NOT "D".

2. Step 2: Use $nor to exclude documents with qty 0 or status "D"

   { $nor: [ { qty: 0 }, { status: "D" } ] } excludes documents with qty 0 or status "D", so it returns documents matching the requirement.

3. Final Answer:

   { $nor: [ { qty: 0 }, { status: "D" } ] } -> Option A

4. Quick Check:

   Exclude unwanted values with $nor = D [OK]

Hint: Use $nor to exclude unwanted values directly [OK]

Common Mistakes:

• Using $ne inside $nor incorrectly
• Confusing inclusion with exclusion logic
• Using wrong comparison operators inside conditions