Update & Delete

// Update operators
db.users.updateOne(
  { _id: ObjectId("...") },
  { $set: { lastLogin: new Date() },
    $inc: { loginCount: 1 },
    $push: { logins: new Date() } }
);

// Update many documents
db.products.updateMany(
  { category: "books" },
  { $mul: { price: 0.9 } }      // 10% discount
);

// Upsert
db.users.updateOne(
  { email: "[email protected]" },
  { $setOnInsert: { createdAt: new Date() },
    $set: { name: "Alice" } },
  { upsert: true }
);

// Delete
db.users.deleteOne({ _id: ObjectId("...") });
db.users.deleteMany({ inactive: true });