PCDE Practice Question: Manage a solution that can span multiple database technologies
A team is using Firestore in Native mode. They have a collection 'users' with an array field 'roles'. They need to query all users where roles contains 'admin'. What index configuration is required?
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 an index exemption on the 'roles' field.
Firestore supports array membership queries using the 'array-contains' operator. An index exemption for the array field is required because Firestore does not automatically index array fields for array-contains queries. The exemption is created manually.
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 single-field index on roles with ascending order.
Why it's wrong here
A single-field index does not support array-contains; an exemption is needed to override the default no-index for arrays.
- ✓
Create an index exemption on the 'roles' field.
Why this is correct
Correct. An index exemption is required for array fields to support array-contains queries.
- ✗
Create a composite index on roles and the default field.
Why it's wrong here
Array-contains queries require a single-field index exemption for the array field, not a composite index.
- ✗
No index is needed; Firestore automatically supports array-contains queries.
Why it's wrong here
Firestore does not automatically index array fields for array-contains; an index exemption is needed.
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