Update Documents

Introduction

Updates in MongoDB are atomic per document and use update operators rather than rewriting whole documents. $set, $inc, $push, $unset — each does one job, surgically.

Syntax reference

// Set + increment
db.users.updateOne(
  { _id: 1 },
  { $set: { lastLogin: new Date() }, $inc: { loginCount: 1 } }
);

// Many
db.products.updateMany({ stock: { $lt: 5 } }, { $set: { lowStock: true } });

// Upsert
db.counters.updateOne({ _id: "orders" }, { $inc: { seq: 1 } }, { upsert: true });

Real-world use

Every 'increment likes' or 'mark read' button in a UI maps to one update operator.

Best practices

• Use $inc for counters — atomic and safe under concurrency.
• Use upsert: true for 'insert if missing'.