C100DBA Philosophy and Features Practice Question
Exhibit
db.products.insert({name: 'Laptop', price: 1000, tags: ['electronics', 'work']})Refer to the exhibit. What is the primary benefit of the data structure shown?
⚠ Common exam trap
Candidates often confuse array indexing with secondary indexes, assuming arrays cannot be queried efficiently, or mistakenly thinking that arrays require a separate collection to maintain relational integrity.
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
✓
It allows for indexing the array to support efficient queries.
The exhibit illustrates the use of an array field within a document. By embedding 'tags' directly into the product document, the application can index and query these items without requiring a separate collection or a join. This design effectively demonstrates how the document model supports efficient data retrieval for common filtering patterns, ensuring that the database scales horizontally while keeping related data units cohesive and performant.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
It forces data normalization for better storage efficiency.
Why it's wrong here
This approach is the opposite of normalization. By embedding the array directly, the data is denormalized. While this can increase storage usage slightly, it significantly improves read performance by avoiding joins, which is a deliberate trade-off in MongoDB to favor application performance and data locality.
- ✓
It allows for indexing the array to support efficient queries.
Why this is correct
MongoDB supports multi-key indexes on array fields. By embedding tags in an array, you can create an index that allows for extremely fast lookups of all documents containing specific tags, which would be difficult and slow to perform if the tags were stored in a separate table.
- ✗
It enforces referential integrity between products and tags.
Why it's wrong here
Referential integrity is not enforced for embedded data structures. MongoDB does not automatically validate the existence of tags or maintain links between collections. This responsibility is delegated to the application layer, which is a common trade-off for the performance gains achieved by avoiding cross-collection relational constraints.
- ✗
It requires a multi-document transaction to update the tags.
Why it's wrong here
Updating an array within a single document is an atomic operation performed on that document. No multi-document transaction is required. Because the update is scoped to one document, it is highly efficient and avoids the performance penalties associated with distributed transaction coordination across multiple collections or nodes.
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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
This C100DBA 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 C100DBA exam.