PCDE Practice Question: Manage a solution that can span multiple database technologies
A developer wants to add a composite index in Firestore to support a query that filters on two fields: 'status' (equality) and 'createdAt' (range). How should the index be configured?
⚠ Common exam trap
The PCDOE exam often tests the misconception that the order of fields in a composite index does not matter, but Firestore strictly requires the equality field to precede the range field to avoid a full collection scan.
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 with fields 'status' (ascending) and 'createdAt' (ascending).
Firestore requires a composite index when a query combines an equality filter on one field with a range filter on another. The index must list the equality field first ('status') followed by the range field ('createdAt'), with ascending order for both to support the range query efficiently. This matches the Firestore index definition rules for composite indexes.
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 a composite index with fields 'status' (ascending) and 'createdAt' (ascending).
Why this is correct
This composite index configuration supports equality on 'status' and range on 'createdAt'.
- ✗
No index is needed; single-field indexes are automatically created.
Why it's wrong here
Single-field indexes are automatic, but a composite index is required for queries on multiple fields.
- ✗
Create a composite index with fields 'createdAt' (ascending) and 'status' (ascending).
Why it's wrong here
The order must place equality fields first. Reverse order would not support the query efficiently.
- ✗
Add an index exemption on the 'status' field to force index creation.
Why it's wrong here
Index exemptions are for excluding specific fields from automatic indexing, not for creating composite indexes.
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