C100DBA Philosophy and Features Practice Question
A media company stores articles with nested comments and tags. The development team wants to retrieve an article along with its comments in a single database round trip. Which MongoDB philosophy supports this design?
⚠ Common exam trap
The trap here is assuming that referencing with manual joins is equivalent to embedding, when only embedding guarantees a single-round-trip retrieval.
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
✓
Embedding related data within a single document
Embedding related data such as comments and tags within the article document allows the application to retrieve everything in one query. This reduces round trips and latency, directly supporting the team's goal of a single database call to render an article page.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Using a relational foreign key constraint between articles and comments
Why it's wrong here
MongoDB does not enforce foreign key constraints between collections. While you can reference documents by ID, this still requires multiple queries to retrieve the related data. The requirement for a single round trip is better met by embedding, not by mimicking relational foreign keys.
- ✓
Embedding related data within a single document
Why this is correct
Embedding related data within a single document allows the article, its comments, and tags to be stored together. A single query on the article document returns all embedded data, eliminating the need for multiple round trips. This matches MongoDB's document model philosophy of keeping related data together for efficient access.
- ✗
Storing comments as a comma-separated string in a single field
Why it's wrong here
Storing comments as a comma-separated string in a single field makes it difficult to query, update, or index individual comments. It also loses the structured nature of comment data, such as author and timestamp. This approach does not align with MongoDB's document model, which supports arrays of subdocuments for structured nesting.
- ✗
Normalizing comments into a separate collection with manual joins
Why it's wrong here
Normalizing comments into a separate collection with manual joins requires the application to issue multiple queries and combine results. This increases complexity and latency, and it does not leverage MongoDB's ability to store related data together. The team specifically wants a single round trip, which this approach cannot provide.
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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
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