What is Projection Operators?

0-2 years experience

1. 1We have a collection of user documents with fields name, email, password, and address. How would you write a query to return only name and email, excluding the password?
2. 2If you run db.users.find({}, { _id: 0, name: 1, email: 1 }), what will the result look like and why?

2-5 years experience

1. 1Our API endpoint started returning the password hash after a recent change. Walk me through how you'd use a projection operator to fix the response and what you'd verify to prevent a recurrence.
2. 2A new field 'lastLogin' was added, but a downstream service that expects only name and email began failing due to extra fields. How would you adjust the projection, and what trade‑offs exist between inclusion and exclusion syntax?

5-8 years experience

1. 1Our analytics pipeline processes millions of order documents, but we only need orderId, total, and customerId. Explain how you'd design the MongoDB query with projection to minimize network I/O and CPU, and discuss any index considerations.
2. 2In a sharded cluster we must enforce field‑level security so certain users never see the 'salary' field. How would you implement projection at the query layer, and what are the performance implications across shards?

8+ years experience

1. 1We're migrating a legacy monolith to microservices, each with its own read‑only view of the data. How would you architect a shared data‑access library that uses projection operators to enforce contract boundaries and reduce payload size while staying maintainable across teams?
2. 2Our organization wants a global policy to ensure GDPR‑restricted PII fields are never sent over the wire. Describe how you'd design a policy‑driven projection system that can be applied everywhere, and what challenges you anticipate during rollout and backward compatibility.