$currentDate¶

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Definition
Behavior
Example

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:

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{ $currentDate: { <field1>: <typeSpecification1>, ... } }

<typeSpecification> can be either:

a boolean true to set the field value to the current date as a Date, or
a 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¶

If the field does not exist, $currentDate adds the field to a document.

Example¶

Create a sample collection customers with the following document:

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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".

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db.customers.updateOne(
   { _id: 1 },
   {
     $currentDate: {
        lastModified: true,
        "cancellation.date": { $type: "timestamp" }
     },
     $set: {
        "cancellation.reason": "user request",
        status: "D"
     }
   }
)

After the operation, you can query the collection to verify the update:

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db.customers.find().pretty()

The updated document would resemble:

{
   "_id" : 1,
   "status" : "D",
   "lastModified" : ISODate("2020-01-22T21:21:41.052Z"),
   "cancellation" : {
      "date" : Timestamp(1579728101, 1),
      "reason" : "user request"
   }
}

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 and CLUSTER_TIME values remain the same throughout the pipeline.

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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:

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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"
   }
}

$currentDate¶

Definition¶

Behavior¶

Example¶

Aggregation Alternative to $currentDate¶

Aggregation Alternative to `$currentDate`¶