$inc (update operator)

Definition

$inc

The $inc operator increments a field by a specified value.

Compatibility

You can use $inc for deployments hosted in the following environments:

• MongoDB Atlas: The fully managed service for MongoDB deployments in the cloud

• MongoDB Enterprise: The subscription-based, self-managed version of MongoDB

• MongoDB Community: The source-available, free-to-use, and self-managed version of MongoDB

Syntax

The $inc operator has the following form:

{ $inc: { <field1>: <amount1>, <field2>: <amount2>, ... } }

To specify a <field> in an embedded document or in an array, use dot notation.

Behavior

Starting in MongoDB 5.0, update operators process document fields with string-based names in lexicographic order. Fields with numeric names are processed in numeric order. See Update Operators Behavior for details.

The $inc operator accepts positive and negative values.

If the field does not exist, $inc creates the field and sets the field to the specified value.

Using the $inc operator on a field with a null value generates an error.

$inc is an atomic operation within a single document.

Starting in MongoDB 5.0, mongod no longer raises an error when you use an update operator like $inc with an empty operand expression ( { } ). An empty update results in no changes and no oplog entry is created (meaning that the operation is a no-op).

Example

Create the products collection:

db.products.insertOne(   {     _id: 1,     sku: "abc123",     quantity: 10,     metrics: { orders: 2, ratings: 3.5 }   })

The following updateOne() operation uses the $inc operator to:

• increase the "metrics.orders" field by 1

• increase the quantity field by -2 (which decreases quantity)

db.products.updateOne(   { sku: "abc123" },   { $inc: { quantity: -2, "metrics.orders": 1 } })

The operation returns the following result:

{  _id: 1,  sku: 'abc123',  quantity: 8,  metrics: { orders: 3, ratings: 3.5 }}