findOne() — MongoDB Technical Interview Questions & Answers

Returns the first document matching a filter.

findOne()

  • Simple meaning: findOne returns the first matching document or null — not a cursor.
  • How to use: db.students.findOne({ roll: 12 }).
  • Try this: findOne missing roll — you get null. Good for “load this student”.
  • Common mistake: findOne without filter when many docs exist — you get an arbitrary first document.
  • Interview tip: One document or null. find() is many.

Technical Interview Tip: findOne({ roll: 12 }) vs find().

Code Examples for findOne()

findOne() — working example

db.users.findOne(
  { email: "ada@example.com" },
  { name: 1, email: 1, skills: 1, _id: 0 }
)

findOne() — findOne returns a single document (or null), not a cursor.

How to Explain findOne() to an Interviewer

find vs findOne?

find = cursor of many findOne = one document or null