$min and $max update operators in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to update the field 'score' only if the new value is less than the current value using the $min operator.

MongoDB

db.collection.updateOne({ _id: 1 }, { $[1]: { score: 50 } })

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

Ainc

Bmax

Cset

Dmin

Attempts:

3 left

💡 Hint

Common Mistakes

Using $max instead of $min will update only if the new value is greater.

Using $set will always update regardless of value.

The $min operator updates the field only if the specified value is less than the current field value.

2fill in blank

medium

Complete the code to update the field 'score' only if the new value is greater than the current value using the $max operator.

MongoDB

db.collection.updateOne({ _id: 2 }, { $[1]: { score: 80 } })

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

Amax

Bmin

Cset

Dinc

Attempts:

3 left

💡 Hint

Common Mistakes

Using $min will update only if the new value is smaller.

Using $set will overwrite the value regardless.

The $max operator updates the field only if the new value is greater than the current value.

3fill in blank

hard

Fix the error in the update command to use the correct operator that updates 'level' only if the new value is greater.

MongoDB

db.collection.updateOne({ _id: 3 }, { $[1]: { level: 10 } })

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

Amin

Bmax

Cset

Dinc

Attempts:

3 left

💡 Hint

Common Mistakes

Using $min instead of $max.

Using $set which always updates.

To update only if the new value is greater, use $max. Using $min or $set would not achieve this.

4fill in blank

hard

Fill both blanks to update 'score' to 40 only if it is less than current, and 'rank' to 5 only if it is greater than current.

MongoDB

db.collection.updateOne({ _id: 4 }, { $[1]: { score: 40 }, $[2]: { rank: 5 } })

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

Amin

Bset

Cmax

Dinc

Attempts:

3 left

💡 Hint

Common Mistakes

Using $set for both fields updates unconditionally.

Mixing up $min and $max operators.

Use $min to update 'score' only if 40 is less than current, and $max to update 'rank' only if 5 is greater than current.

5fill in blank

hard

Fill all three blanks to update 'score' to 30 if less, 'level' to 15 if greater, and 'rank' to 2 if less.

MongoDB

db.collection.updateOne({ _id: 5 }, { $[1]: { score: 30, rank: 2 }, $[2]: { level: 15 }, $[3]: { extra: 100 } })

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

Amin

Bmax

Cset

Dinc

Attempts:

3 left

💡 Hint

Common Mistakes

Using $set for all fields ignores conditional updates.

Confusing which fields need $min or $max.

Use $min for 'score' and 'rank' to update if new values are less, $max for 'level' to update if greater, and $set for 'extra' to always update.

Practice

1. What does the $min update operator do in MongoDB?

easy

A. Updates the field only if the new value is smaller than the current value.

B. Updates the field only if the new value is larger than the current value.

C. Always updates the field with the new value.

D. Deletes the field if the new value is smaller.

Solution

1. Step 1: Understand the purpose of $min

   The $min operator updates a field only if the new value is smaller than the current value stored in that field.

2. Step 2: Compare with other options

   $max updates if the new value is larger, and other options do not match the behavior of $min.

3. Final Answer:

   Updates the field only if the new value is smaller than the current value. -> Option A

4. Quick Check:

   $min updates only if smaller [OK]

Hint: Remember: $min means update if new value is smaller [OK]

Common Mistakes:

• Confusing $min with $max behavior
• Thinking $min always updates the field
• Assuming $min deletes fields

2. Which of the following is the correct syntax to use $max to update the field score to 90 in MongoDB?

easy

A. { $max: [ score: 90 ] }

B. { $max: score: 90 }

C. { $max: { score: 90 } }

D. { $max: { 'score' => 90 } }

Solution

1. Step 1: Recall correct MongoDB update syntax

   MongoDB update operators use the format: { $operator: { field: value } }. So $max must be followed by an object with field and value.

2. Step 2: Check each option

   { $max: { score: 90 } } matches the correct syntax. The options missing braces around the field-value pair or using brackets [] have invalid syntax. { $max: { 'score' => 90 } } uses '=>' which is not valid in MongoDB queries.

3. Final Answer:

   { $max: { score: 90 } } -> Option C

4. Quick Check:

   Correct MongoDB update syntax = { $max: { score: 90 } } [OK]

Hint: Use braces { } around field-value pairs in update operators [OK]

Common Mistakes:

• Using brackets [] instead of braces {}
• Missing braces around field-value pairs
• Using arrow syntax '=>' instead of colon ':'

3. Given a document { _id: 1, highScore: 80 }, what will be the document after applying db.collection.updateOne({_id:1}, { $max: { highScore: 75 } })?

medium

A. { _id: 1, highScore: 75 }

B. { _id: 1, highScore: 155 }

C. No document updated

D. { _id: 1, highScore: 80 }

Solution

1. Step 1: Understand $max behavior on existing value

   The $max operator updates the field only if the new value is greater than the current value. Here, current highScore is 80, new value is 75.

2. Step 2: Compare values and decide update

   Since 75 is less than 80, the field will NOT be updated. The document remains unchanged.

3. Final Answer:

   { _id: 1, highScore: 80 } -> Option D

4. Quick Check:

   $max updates only if new value is larger [OK]

Hint: If new value < current, $max does not update [OK]

Common Mistakes:

• Assuming $max always updates the field
• Confusing $max with $min behavior
• Thinking update fails if condition not met

4. You run this update: db.collection.updateOne({_id: 2}, { $min: { age: 30 } }) but it does not update the document. What could be the reason?

medium

A. The update syntax is incorrect.

B. The current age in the document is less than 30.

C. The document with _id: 2 does not exist.

D. The $min operator requires an array value.

Solution

1. Step 1: Understand $min update condition

   $min updates the field only if the new value is smaller than the current value.

2. Step 2: Analyze why update might not happen

   If the current age is already less than 30, the update will not change the document. Other options are incorrect because $min does not require arrays, the syntax is correct, and the question states the update runs but no change occurs.

3. Final Answer:

   The current age in the document is less than 30. -> Option B

4. Quick Check:

   $min updates only if new value smaller [OK]

Hint: No update if current value is smaller than $min value [OK]

Common Mistakes:

• Thinking $min requires array values
• Assuming syntax error without checking
• Ignoring existing document values

5. You want to keep track of the lowest and highest temperatures recorded in a MongoDB document with fields minTemp and maxTemp. Which update operation correctly updates both fields when a new temperature temp is 15?

hard

A. { $min: { minTemp: 15 }, $max: { maxTemp: 15 } }

B. { $max: { minTemp: 15 }, $min: { maxTemp: 15 } }

C. { $min: { maxTemp: 15 }, $max: { minTemp: 15 } }

D. { $set: { minTemp: 15, maxTemp: 15 } }

Solution

1. Step 1: Understand the goal for minTemp and maxTemp

   We want minTemp to update only if the new temperature is lower, so use $min. For maxTemp, update only if new temperature is higher, so use $max.

2. Step 2: Check each option for correct operator usage

   { $min: { minTemp: 15 }, $max: { maxTemp: 15 } } correctly uses $min for minTemp and $max for maxTemp. { $max: { minTemp: 15 }, $min: { maxTemp: 15 } } and { $min: { maxTemp: 15 }, $max: { minTemp: 15 } } swap operators incorrectly. { $set: { minTemp: 15, maxTemp: 15 } } always sets both fields to 15, ignoring previous values.

3. Final Answer:

   { $min: { minTemp: 15 }, $max: { maxTemp: 15 } } -> Option A

4. Quick Check:

   Use $min for minTemp and $max for maxTemp [OK]

Hint: Use $min for minimum and $max for maximum fields [OK]

Common Mistakes:

• Swapping $min and $max operators
• Using $set which overwrites values blindly
• Updating wrong fields with wrong operators