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$inc

$inc

The $inc operator increments a field by a specified value and has the following form:

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

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

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.

Consider a collection products with the following document:

{
_id: 1,
sku: "abc123",
quantity: 10,
metrics: {
orders: 2,
ratings: 3.5
}
}

The following update() operation uses the $inc operator to decrease the quantity field by 2 (i.e. increase by -2) and increase the "metrics.orders" field by 1:

db.products.update(
{ 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
}
}
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  • Definition
  • Behavior
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