Suposse tou have the following collection with only 2 documents: If you run an aggregation query and use { $unwind: "$traits" } as the first stage, how many documents will be passed to the next…

The correct answer is B. 5. $unwind deconstructs an array field by outputting one document per array element - so the total output depends on the combined number of elements across all traits arrays in the collection. With the two documents shown, the traits arrays contain a combined total of 5 elements…

MongoDB Fundamentals

Question

Suposse tou have the following collection with only 2 documents:

If you run an aggregation query and use { $unwind: "$traits" } as the first stage, how many documents will be passed to the next stage of the aggregation pipeline?

Exhibit

Options

How the community answered

(50 responses)

A
2% (1)
B
72% (36)
C
14% (7)
D
4% (2)
E
8% (4)

Explanation

$unwind deconstructs an array field by outputting one document per array element - so the total output depends on the combined number of elements across all traits arrays in the collection. With the two documents shown, the traits arrays contain a combined total of 5 elements, which is why 5 documents are passed to the next stage.

Why the distractors are wrong:

D (2) is the most tempting trap - it's the original document count, but $unwind expands documents, it does not preserve the original count.
C (4) and A (3) likely match the element count of just one of the two documents' traits arrays, ignoring the contribution of the other.
E (1) has no basis - $unwind never collapses documents.

Memory tip: Think of $unwind as a zipper being pulled apart - each tooth in the array becomes its own document. Count all array elements across all documents to get the output count, not the number of documents.

Topics

#aggregation pipeline#$unwind#array unwinding#document count

Community Discussion

No community discussion yet for this question.

Full C100DBA Practice