Update Operators: $inc

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$inc

Definition

$inc The $inc operator increments a field by a specified value and has the following form: { $inc: { <field1>: <amount1>} } To specify a in an embedded document or in an array, use dot notation.

Behavior

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.

Example

Consider a collection products with the following document:

{
  id: 123,
  name: "Corn Flakes",
  inventory: 5,
  metrics: {
    minQty: 2,
    reOrderQty: 10,
    totalSold: 55
  }
}

The following update() operation uses the $inc operator to decrease the quantity field by 1 (i.e. increase by -1) and increase the "metrics.totalSold" field by 1:

buildfire.datastore.update(
   { id: 123 },
   { $inc: { inventory: -1 } ,$inc: {"metrics.totalSold": 1} }
);

The updated document would resemble:

{
  id: 123,
  name: "Corn Flakes",
  inventory: 4,
  metrics: {
    minQty: 2,
    reOrderQty: 10,
    totalSold: 56
  }
}