Array update with positional $ operator in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the positional $ operator do in a MongoDB update?

It updates the first array element that matches the query condition inside a document.

beginner

How do you use the positional $ operator in an update query?

Use it in the update document like { $set: { 'arrayField.$': newValue } } where the query matches an element in arrayField.

intermediate

Can the positional $ operator update multiple array elements at once?

No, it only updates the first matching element in the array for the query.

beginner

Example: Update the score of the first game named 'chess' in a player's games array.

Query: { 'games.name': 'chess' }<br>Update: { $set: { 'games.$.score': 100 } }

intermediate

What happens if no array element matches the query when using the positional $ operator?

No update occurs because the operator only works if a matching element is found.

What does the positional $ operator update in MongoDB?

A The first matching element in an array

B All elements in an array

C The entire document

D Only the last element in an array

The positional $ operator updates only the first array element that matches the query condition.

Which of the following is the correct syntax to update the first matching element's field 'score' in array 'games'?

A { $set: { 'games.$.score': 50 } }

B { $set: { 'games.score.$': 50 } }

C { $set: { 'games.score': 50 } }

D { $set: { 'games.$score': 50 } }

The positional $ operator goes after the array name and before the field to update.

If the query does not match any array element, what happens when using the positional $ operator?

A The first element is updated anyway

B No update is performed

C An error is thrown

D All elements are updated

No update occurs because the operator requires a matching element.

Can the positional $ operator update multiple array elements in one update?

A Yes, it updates all matching elements

B Yes, but only if specified

C No, only the first matching element

D No, it updates the whole array

It only updates the first matching element found.

Which MongoDB update operator is commonly used with the positional $ operator to change a field value?

A $inc

B $unset

C $push

D $set

$set is used to assign a new value to a field.

Explain how the positional $ operator works in MongoDB array updates.

Think about how you find and update one item in a list.

Describe a real-life example where you would use the positional $ operator to update an array element.

Imagine you want to change one score in a list of game scores.