MongoDB $inc Operator

The $inc operator in MongoDBdatabase atomically increments or decrements numeric fields by a specified value, making it ideal for counters, scores, and inventory updates while ensuring data consistency.

• Atomic Updates: Performs safe, in-place numeric updates within a document.
• Increment & Decrement: Supports both positive and negative values.
• Auto Field Creation: Creates the field if it doesn’t exist and sets it to the increment value.
• Numeric Fields Only: Works with numeric types, using it on null or non-numeric fields causes an error.
• High Concurrency Safe: Prevents race conditions when multiple updates occur.

Syntax

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

MongoDB $inc Operator Example

We'll use a sample database called GeeksforGeeks, which contains a contributor collection.

• Database: GeeksforGeeks
• Collection: contributor
• Document: Three documents that contain the details of the contributors in the form of field-value pairs

Example 1: Incrementing a Field Value

Updating the fields of a contributor's document whose name is Lucas by incrementing the value of the publisharticles field by 10 and decreasing the value of the salary field by 100.

db.contributor.updateOne({ name: "Lucas" }, { $inc: { publisharticles: 10, salary: -100 } })

Output:

Example 2: Incrementing a Field in an Array Element

Update the value of a nested field a in the array points, for a specific document where the name is "Sophia" and the points._id is "g_1"

db.contributor.updateOne({name: "Sophia" , "points._id" : "g_1"}, {$inc: {"points.$.a":10}})

Output:

Example 3: Incrementing a Field in an Embedded Document

Increment the value of the rank field in an embedded document personal for a document where the name is "Oliver".

db.contributor.updateOne({name: "Oliver"}, {$inc: {"personal.rank": 2}})

Output:

Important Points for using $inc Operator

These points highlight how $inc handles field creation, errors, and atomic updates to maintain data consistency.

• Field Creation: Creates the field if it doesn’t exist and sets the increment value.
• Null Fields: Fails on null or non-numeric fields.
• Atomic Update: Applies changes atomically to avoid concurrency issues.