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$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
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 $inc
with 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).
Example
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 1increase the
quantity
field by -2 (which decreasesquantity
)
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 } }