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PCDE Practice Question: Design innovative, scalable, and highly available cloud database solutions
A team is migrating a MongoDB application to Firestore. The data model includes embedded documents and references between collections. Which approach should they follow to maintain similar query performance?
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
✓
Use subcollections for embedded data and references for relationships
Firestore supports subcollections (similar to embedded documents) and references. Denormalization can reduce the need for joins. Avoiding transactions for every write is not ideal for consistency. The recommended pattern is to use subcollections for embedded data and references for related entities.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Flatten all data into a single document per entity
Why it's wrong here
This defeats the purpose of NoSQL and may cause document size limits.
- ✗
Replicate data across multiple collections to avoid reads
Why it's wrong here
Data duplication increases complexity and storage costs.
- ✓
Use subcollections for embedded data and references for relationships
Why this is correct
Subcollections preserve the embedded document structure; references handle relationships.
- ✗
Use a single collection for all documents and rely on client-side joins
Why it's wrong here
Client-side joins are inefficient and not scalable.
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