$inc (original) (raw)

$inc

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

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

The $inc operator has the following form:


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

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

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.

Use of the $inc operator on a field with a null value will generate 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 $incwith 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).

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 updated document would resemble:


{

  _id: 1,

  sku: 'abc123',

  quantity: 8,

  metrics: { orders: 3, ratings: 3.5 }

}