Combining logical and comparison operators in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to find documents where age is greater than 25.

MongoDB

db.collection.find({ age: { $[1]: 25 } })

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

Alt

Beq

Cne

Dgt

Attempts:

3 left

💡 Hint

Common Mistakes

Using $lt instead of $gt will find ages less than 25.

Using $eq will find ages exactly 25, not greater.

The operator $gt means 'greater than'. So this query finds documents where the age field is greater than 25.

2fill in blank

medium

Complete the code to find documents where status is 'active' and score is at least 80.

MongoDB

db.collection.find({ $and: [ { status: '[1]' }, { score: { $gte: 80 } } ] })

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

Aactive

Binactive

Cpending

Dclosed

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'inactive' will find the wrong documents.

Leaving the status value empty will cause an error.

The query uses $and to combine conditions. We want status to be 'active', so we fill in 'active'.

3fill in blank

hard

Fix the error in the query to find documents where age is less than 30 or score is greater than 90.

MongoDB

db.collection.find({ $or: [ { age: { $[1]: 30 } }, { score: { $gt: 90 } } ] })

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

Alte

Beq

Clt

Dgte

Attempts:

3 left

💡 Hint

Common Mistakes

Using $gte will find ages greater than or equal to 30, which is wrong here.

Using $eq will only find age exactly 30.

The operator $lt means 'less than'. We want age less than 30, so $lt is correct.

4fill in blank

hard

Fill both blanks to find documents where status is 'pending' and age is not equal to 40.

MongoDB

db.collection.find({ $and: [ { status: '[1]' }, { age: { $[2]: 40 } } ] })

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

Apending

Bactive

Cne

Deq

Attempts:

3 left

💡 Hint

Common Mistakes

Using $eq instead of $ne will find age exactly 40, not excluding it.

Using wrong status value will find wrong documents.

The query uses $and to combine conditions. Status should be 'pending' and age should not equal 40, so we use $ne for 'not equal'.

5fill in blank

hard

Fill all three blanks to find documents where name starts with 'J', age is greater than 20, and score is less than or equal to 100.

MongoDB

db.collection.find({ $and: [ { name: { $regex: '^[1]' } }, { age: { $[2]: 20 } }, { score: { $[3]: 100 } } ] })

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

AJ

Bgt

Clte

Dlt

Attempts:

3 left

💡 Hint

Common Mistakes

Using $lt instead of $gt for age will find wrong documents.

Using $lt instead of $lte for score excludes 100.

The regex ^J matches names starting with 'J'. Age should be greater than 20, so $gt. Score should be less than or equal to 100, so $lte.

Practice

1. Which MongoDB operator is used to combine multiple conditions where all must be true?

easy

A. $gt

B. $and

C. $or

D. $lt

Solution

1. Step 1: Understand logical operators

   $and requires all conditions inside it to be true for a document to match.

2. Step 2: Compare with other operators

   $or requires any condition to be true, $gt and $lt are comparison operators, not logical combiners.

3. Final Answer:

   $and -> Option B

4. Quick Check:

   All conditions true = $and [OK]

Hint: Use $and to require all conditions true [OK]

Common Mistakes:

• Confusing $and with $or
• Using comparison operators as logical
• Mixing $gt with $and

2. Which of the following is the correct syntax using $and to find documents where age is greater than 25 and status is 'active'?

easy

A. { $and: [ { age: { $gt: 25 } }, { status: 'active' } ] }

B. { $or: [ { age: { $gt: 25 } }, { status: 'active' } ] }

C. { age: { $gt: 25 }, status: 'active' }

D. { $and: { age: { $gt: 25 }, status: 'active' } }

Solution

1. Step 1: Check $and syntax

   $and requires an array of conditions, so the value must be an array of objects.

2. Step 2: Validate other options

   { $or: [ { age: { $gt: 25 } }, { status: 'active' } ] } uses $or, { age: { $gt: 25 }, status: 'active' } uses implicit AND but not with $and operator, { $and: { age: { $gt: 25 }, status: 'active' } } uses $and with an object instead of array which is invalid.

3. Final Answer:

   { $and: [ { age: { $gt: 25 } }, { status: 'active' } ] } -> Option A

4. Quick Check:

   $and needs array of conditions [OK]

Hint: Use array inside $and for multiple conditions [OK]

Common Mistakes:

• Using object instead of array in $and
• Confusing $and with $or
• Missing $gt operator syntax

3. Given the collection documents: [{ age: 30, status: 'active' }, { age: 20, status: 'inactive' }, { age: 40, status: 'active' }], what documents match this query?
{ $or: [ { age: { $lt: 25 } }, { status: 'active' } ] }

medium

A. [{ age: 30, status: 'active' }, { age: 40, status: 'active' }]

B. []

C. [{ age: 20, status: 'inactive' }]

D. [{ age: 20, status: 'inactive' }, { age: 30, status: 'active' }, { age: 40, status: 'active' }]

Solution

1. Step 1: Understand $or condition

   Documents match if age is less than 25 OR status is 'active'.

2. Step 2: Check each document

   First doc: age 30 (not <25), status 'active' (matches). Second doc: age 20 (<25), status 'inactive' (matches age condition). Third doc: age 40 (not <25), status 'active' (matches).

3. Final Answer:

   All three documents match -> Option D

4. Quick Check:

   $or matches any condition true [OK]

Hint: Any condition true in $or returns document [OK]

Common Mistakes:

• Ignoring one condition in $or
• Confusing $or with $and
• Wrongly excluding documents

4. Identify the error in this MongoDB query to find documents where score is greater than 50 and less than 100:
{ $and: { score: { $gt: 50 }, score: { $lt: 100 } } }

medium

A. Using object instead of array inside $and

B. Using $gt and $lt together is invalid

C. Missing $or operator

D. score field should be inside $or

Solution

1. Step 1: Check $and operator usage

   $and requires an array of condition objects, not a single object with repeated keys.

2. Step 2: Understand object key overwrite

   In the object, 'score' key appears twice, so only the last one is used, causing incorrect query.

3. Final Answer:

   Using object instead of array inside $and -> Option A

4. Quick Check:

   $and needs array, not object with duplicate keys [OK]

Hint: Use array for $and conditions to avoid key overwrite [OK]

Common Mistakes:

• Using object with duplicate keys in $and
• Confusing $and with $or
• Thinking $gt and $lt can't combine

5. You want to find documents where (age is greater than 30 and status is 'active') or (score is less than 50). Which query correctly combines these conditions?

hard

A. { $and: { $or: [ { age: { $gt: 30 } }, { status: 'active' } ], score: { $lt: 50 } } }

B. { $and: [ { age: { $gt: 30 } }, { status: 'active' }, { score: { $lt: 50 } } ] }

C. { $or: [ { $and: [ { age: { $gt: 30 } }, { status: 'active' } ] }, { score: { $lt: 50 } } ] }

D. { $or: { age: { $gt: 30 }, status: 'active', score: { $lt: 50 } } }

Solution

1. Step 1: Break down the condition

   We want documents matching either (age > 30 AND status = 'active') OR (score < 50).

2. Step 2: Match query structure

   { $or: [ { $and: [ { age: { $gt: 30 } }, { status: 'active' } ] }, { score: { $lt: 50 } } ] } uses $or with two parts: one $and array for age and status, and one condition for score less than 50, matching the requirement exactly.

3. Final Answer:

   { $or: [ { $and: [ { age: { $gt: 30 } }, { status: 'active' } ] }, { score: { $lt: 50 } } ] } -> Option C

4. Quick Check:

   Nested $and inside $or matches complex logic [OK]

Hint: Use nested $and inside $or for combined conditions [OK]

Common Mistakes:

• Using $and instead of $or for main condition
• Wrong object instead of array syntax
• Mixing $or and $and incorrectly