- A
Use resource.data to access the document's fields.
Correct. resource.data gives access to the current document's fields, such as 'ownerId'.
- B
Use request.resource to validate incoming data during writes.
Correct. request.resource represents the incoming data during writes, allowing validation that the new ownerId matches the user's UID.
- C
Write a rule that allows read if request.auth.uid == resource.data.ownerId.
Why wrong: Incorrect. While the rule uses components A and E, it is a full rule statement, not a component itself.
- D
Use the exists() function to check if the ownerId field exists.
Why wrong: Incorrect. exists() checks if a document exists, not if a field matches the owner's UID.
- E
Use request.auth to verify user identity.
Correct. request.auth provides the authenticated user's UID to compare against the ownerId field.
PCD resource.data Practice Question
This PCD practice question tests your understanding of deploy scalable and highly available databases in google cloud. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. A key principle to apply: resource.data. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A team is using Firestore for a mobile application. They need to write security rules that allow users to read and write only their own documents. The documents have a field 'ownerId' that matches the user's UID. Which THREE rule components should they use? (Choose 3.)
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 resource.data to access the document's fields.
The three core components for Firestore security rules that allow users to read/write only their own documents are: (A) resource.data to access document fields, (B) request.resource to validate incoming write data, and (E) request.auth to verify the user's identity. Option C is a complete rule that combines A and E, not a separate component. Option D is incorrect because exists() checks document existence, not field matching.
Key principle: resource.data
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Use resource.data to access the document's fields.
Why this is correct
Correct. resource.data gives access to the current document's fields, such as 'ownerId'.
Related concept
resource.data
- ✓
Use request.resource to validate incoming data during writes.
Why this is correct
Correct. request.resource represents the incoming data during writes, allowing validation that the new ownerId matches the user's UID.
Related concept
resource.data
- ✗
Write a rule that allows read if request.auth.uid == resource.data.ownerId.
Why it's wrong here
Incorrect. While the rule uses components A and E, it is a full rule statement, not a component itself.
- ✗
Use the exists() function to check if the ownerId field exists.
Why it's wrong here
Incorrect. exists() checks if a document exists, not if a field matches the owner's UID.
- ✓
Use request.auth to verify user identity.
Why this is correct
Correct. request.auth provides the authenticated user's UID to compare against the ownerId field.
Related concept
resource.data
Common exam traps
Common exam trap: answer the scenario, not the keyword
This question asks for 'rule components' (building blocks), not complete rule statements. Option C is a complete rule, not a component.
Detailed technical explanation
How to think about this question
Treat this as a scenario question. Identify the problem, the constraint, and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- resource.data
- request.resource
- request.auth
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
resource.data
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Review resource.data, then practise related PCD questions on the same topic to reinforce the concept.
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FAQ
Questions learners often ask
What does this PCD question test?
Deploy Scalable and Highly Available Databases in Google Cloud — This question tests Deploy Scalable and Highly Available Databases in Google Cloud — resource.data.
What is the correct answer to this question?
The correct answer is: Use resource.data to access the document's fields. — The three core components for Firestore security rules that allow users to read/write only their own documents are: (A) resource.data to access document fields, (B) request.resource to validate incoming write data, and (E) request.auth to verify the user's identity. Option C is a complete rule that combines A and E, not a separate component. Option D is incorrect because exists() checks document existence, not field matching.
What should I do if I get this PCD question wrong?
Review resource.data, then practise related PCD questions on the same topic to reinforce the concept.
What is the key concept behind this question?
resource.data
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Last reviewed: Jul 4, 2026
This PCD practice question is part of Courseiva's free Google Cloud 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 PCD exam.
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