PCDE Practice Question: Manage a solution that can span multiple database technologies
A gaming company uses Firestore in Native mode to store player profiles and game state. They need to query the data by both 'playerId' and 'lastLoginTimestamp' sorted descending. The current index configuration is automatic. How should they configure indexing to support this query efficiently?
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
✓
Create a composite index on 'playerId' ascending and 'lastLoginTimestamp' descending
Firestore automatically creates single-field indexes for all fields. For queries with ordering on two fields, a composite index is required. The composite index must include both fields in the correct order (ascending or descending).
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Create two separate single-field indexes: one on 'playerId' and one on 'lastLoginTimestamp'
Why it's wrong here
Single-field indexes cannot satisfy a query that orders by both fields; a composite index is required.
- ✗
Use an exemption to remove automatic indexing on 'playerId' and rely on single-field indexes
Why it's wrong here
Exemptions are for excluding fields from automatic indexing, not for composite queries.
- ✗
Use the automatic index configuration; Firestore will create the necessary composite index automatically
Why it's wrong here
Firestore only creates single-field indexes automatically; composite indexes must be created manually.
- ✓
Create a composite index on 'playerId' ascending and 'lastLoginTimestamp' descending
Why this is correct
Correct. A composite index with the exact order (asc/desc) is needed for efficient queries with ordering.
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