Array update with $[] all positional in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the $[] operator do in a MongoDB update?

The $[] operator updates all elements in an array. It applies the update to every item inside the array.

beginner

How do you update every element in an array field called scores by adding 5 to each score using $[]?

Use { $inc: { "scores.$[]": 5 } } in the update command. This adds 5 to every element inside the scores array.

intermediate

Can $[] be used without a filter condition inside the array?

Yes. $[] updates all elements in the array regardless of their value or condition. It is an all positional operator.

intermediate

What is the difference between $[] and $[<identifier>] in MongoDB updates?

$[] updates all elements in the array. $[<identifier>] updates only elements that match a specified filter condition.

beginner

Write a MongoDB update query to set all elements in the array tags to the string "updated".

Use { $set: { "tags.$[]": "updated" } } in the update command. This replaces every element in the tags array with "updated".

What does the $[] operator update in MongoDB?

A Only elements matching a filter

B Only the first element in an array

C All elements in an array

D Only the last element in an array

$[] updates all elements in the array, applying the update to each one.

Which update operator would you use to update only specific elements in an array based on a condition?

A $[<identifier>]

B $inc

C $[]

D $set

$[] lets you specify a filter to update only matching array elements.

How would you add 10 to every number in an array field named values?

A { $push: { "values": 10 } }

B { $set: { "values.$[]": 10 } }

C { $inc: { "values": 10 } }

D { $inc: { "values.$[]": 10 } }

Use $inc with $[] to add 10 to every element in the array.

True or False: $[] requires a filter condition to work.

A True

B False

C Only for numeric arrays

D Only for string arrays

$[] updates all elements without needing a filter condition.

What happens if you use { $set: { "items.$[]": null } } in an update?

A All elements in the <code>items</code> array become <code>null</code>

B Only the first element becomes <code>null</code>

C The entire <code>items</code> array is removed

D No change happens

All elements in the items array are set to null using $[].

Explain how the $[] operator works in MongoDB array updates and give an example.

Think about updating every item inside an array at once.

Describe the difference between $[] and $[] in MongoDB updates.

One updates all, the other updates some based on a condition.