C100DEV Aggregation Framework Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✗

  $group with $sum

  Why it's wrong here

  While this method works, it is more verbose than necessary. The $count stage provides a cleaner, more readable syntax for the exact same result. In professional MongoDB development, using the specialized $count stage is preferred for its simplicity and clear intent within the aggregation pipeline structure.

• ✓

  $count

  Why this is correct

  $count is the designated stage for returning a count of documents. It simplifies the pipeline by replacing the need for a $group operation, making it the most efficient and readable choice for counting records after applying any necessary filters in the preceding stages of your aggregation.

• ✗

  $limit

  Why it's wrong here

  $limit is used to restrict the number of documents passed to the next stage, not to count them. It doesn't provide the total number of items, as it stops once the threshold is reached. Therefore, it is entirely inappropriate for calculating a total count of collection records.

• ✗

  $match

  Why it's wrong here

  $match is a filtering operator. It determines which documents are passed forward but does not perform any counting logic. Using it alone will return the documents themselves, not a numeric count, so it cannot fulfill the requirement of returning the total count of documents in the collection.