Mongodb Certified Developer Associate C100dev · Free Practice Question Medium
Question 13
You are working on an e-commerce application that needs to summarize daily sales data and store it in a daily_sales_summary collection. You decide to use the $out operator at the end of your aggregation pipeline to output the results. Which of the following statements is true regarding the behavior and constraints of the $out operator?
-
A
The
$outoperator will completely replace the target collection with the results from the pipeline. -
B
The
$outoperator allows for both inserting new documents and updating existing documents in the target collection. -
C
Using
$outrequires that the aggregation pipeline operates on a sharded cluster -
D
The
$outoperator supports performing additional read and write operations on the output collection during pipeline execution.
Reveal correct answer
Correct answer: A
A.
By default, $out replaces the target collection’s contents with the results from the pipeline, removing any previously existing data. This behavior is essential to know, especially when working with collections containing pre-existing data.
B.
The $out operator does not support selective updating of documents within the target collection. Instead, it either fully replaces the target collection or appends new documents, depending on the target’s existence. Selective updates or upserts are not supported with $out.
C.
The $out operator does not specifically require a sharded cluster. While it can be used on sharded clusters, it is equally functional on replica sets or standalone MongoDB instances.
D.
The $out operator has a locking mechanism that prevents additional read or write operations on the target collection during pipeline execution. This ensures data consistency in the output collection but also temporarily restricts other operations.
Discussion
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