C100DEV Aggregation Framework Practice Question
Exhibit
{
"_id": 1,
"tags": ["red", "blue", "green"]
}Refer to the exhibit. Which stage should be used to transform this document into three separate documents, one for each tag?
⚠ Common exam trap
Candidates often confuse $unwind with $group or $project, mistakenly believing that projection or grouping alone can split array elements into separate individual documents.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
$unwind
The $unwind stage is designed specifically to deconstruct an array field from the input documents to output a document for each element. This is essential for operations like counting occurrences of individual array elements or calculating statistics across specific array items. Without $unwind, the $group stage would treat the entire array as a single value rather than individual components, preventing granular analysis of the array contents.
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
Why it's wrong here
The $group stage is used for aggregating data to compute sums, averages, or other metrics across a collection of documents. It does not possess the capability to deconstruct arrays into individual documents, as its primary purpose is to collapse multiple documents into a single aggregate result per group key.
- ✓
$unwind
Why this is correct
The $unwind stage serves to explode an array into individual documents. By setting preserveNullAndEmptyArrays to false, it generates one document for every item in the array, making it the perfect tool for flattening data structures so that subsequent aggregation stages can process each array element independently.
- ✗
$project
Why it's wrong here
While $project can reshape documents, it cannot multiply the number of documents in a pipeline based on array content. It is meant for field inclusion, exclusion, or computed transformation, but it remains a one-to-one mapping operation and cannot perform the expansion required to isolate individual array elements.
- ✗
$match
Why it's wrong here
The $match stage is a filtering operator used to pass only those documents that meet specified conditions. It has no functionality related to document expansion or array deconstruction; it strictly reduces the document stream rather than modifying the internal structure of the documents that successfully pass through the filter.
About these practice questions
One of 259 original C100DEV practice questions on Courseiva, each with a full explanation and wrong-answer analysis — not exam dumps or protected exam content. Learn why practice questions differ from exam dumps →
JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official MongoDB exam blueprint
This C100DEV practice question is part of Courseiva's free MongoDB certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the C100DEV exam.