$currentDate
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Definition
$currentDate
The
$currentDate
operator sets the value of a field to the current date, either as a Date or a timestamp. The default type is Date.The
$currentDate
operator has the form:{ $currentDate: { <field1>: <typeSpecification1>, ... } } <typeSpecification>
can be either:a boolean
true
to set the field value to the current date as a Date, ora document
{ $type: "timestamp" }
or{ $type: "date" }
which explicitly specifies the type. The operator is case-sensitive and accepts only the lowercase"timestamp"
or the lowercase"date"
.
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.
$currentDate
sets the specified field to the date when
$currentDate
was run.
If the field does not exist, $currentDate
adds the field to a
document.
Starting in MongoDB 5.0, mongod
no longer raises an
error when you use an update operator like $currentDate
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 a sample collection customers
with the following document:
db.customers.insertOne( { _id: 1, status: "a", lastModified: ISODate("2013-10-02T01:11:18.965Z") } )
The following operation updates the lastModified
field to the
current date, the "cancellation.date"
field to the current timestamp
as well as updating the status
field to "D"
and the
"cancellation.reason"
to "user request"
.
db.customers.updateOne( { _id: 1 }, { $currentDate: { lastModified: true, "cancellation.date": { $type: "timestamp" } }, $set: { "cancellation.reason": "user request", status: "D" } } )
$currentDate
sets the specified field to the date when
$currentDate
was run.
To verify the update:
db.customers.find()
The updated document resembles:
{ "_id" : 1, "status" : "D", "lastModified" : ISODate("2020-01-22T21:21:41.052Z"), "cancellation" : { "date" : Timestamp(1579728101, 1), "reason" : "user request" } }
The lastModified
field is set to the date when
$currentDate
was run in the update example shown earlier.
Aggregation Alternative to $currentDate
Starting in version 4.2, update methods can accept an aggregation pipeline. As
such, the previous example can be rewritten as the following using the
aggregation stage $set
and the aggregation variables
NOW
(for the current datetime) and CLUSTER_TIME
(for the current timestamp):
Tip
To access aggregation variables, prefix the variable with double dollar signs
$$
and enclose in quotes.CLUSTER_TIME
is available only on replica sets and sharded clusters.The
NOW
andCLUSTER_TIME
values remain the same throughout the pipeline.
db.customers.updateOne( { _id: 1 }, [ { $set: { lastModified: "$$NOW", cancellation: {date: "$$CLUSTER_TIME", reason: "user request"}, status: "D" } } ] )
After the operation, you can query the collection to verify the update:
db.customers.find().pretty()
The query should return the following document:
{ "_id" : 1, "status" : "D", "lastModified" : ISODate("2020-01-22T21:02:18.994Z"), "cancellation" : { "date" : Timestamp(1579726934, 2), "reason" : "user request" } }