$inc
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Definition
$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.
Behavior
In MongoDB 4.4 and earlier, update operators process document fields in lexicographic 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.
Example
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 } }