Lesson 10 / 22

Update Operators

$set, $inc, and $push — the everyday toolkit.

The common operators

$set sets a field's value, $inc increments a number, $push appends to an array, $unset removes a field.

$inc

Increments (or decrements with a negative value) a numeric field atomically.

db.products.updateOne(
  { name: "Keyboard" },
  { $inc: { stock: -1 } }
)

$push

Appends a new value to an array field.

db.posts.updateOne(
  { _id: postId },
  { $push: { comments: "Great article!" } }
)

Quick check: Which operator increments a numeric field?

  • $set
  • $push
  • $inc
Answer

$inc — $inc atomically adds (or subtracts) a value from a number field.