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- $inc
$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¶
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
}
}
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