Introduction to MongoDB $currentDate Operator

Mongodb is a document-oriented database that supports many different operators for querying and updating documents. One of these operators is the $currentDate operator, which can set a date field in a document to the current date or time.

Syntax

The syntax of the $currentDate operator is as follows:

{ $currentDate: { <field>: <typeSpecification>, ... } }

where <field> specifies the name of the field to be updated, and <typeSpecification> specifies the type of date to be set. <typeSpecification> can be a boolean value or a date type string, such as:

• true to set the date to the current timestamp.
• { $type: "date" } to set the date to the current date.

Use Cases

The $currentDate operator can be used in any update operation, such as updateOne, updateMany, and replaceOne.

When you want to automatically set a date field to the current date or time in an update operation, you can use the $currentDate operator. For example, you can add a lastLogin field to a user document and use $currentDate to set it to the current date when the user logs in.

Examples

Suppose we have a collection named users with the following documents:

{
  "_id": ObjectId("602f5a00b5ff5e89d728c166"),
  "username": "alice",
  "email": "[email protected]",
  "lastLogin": ISODate("2022-02-23T10:23:51.000Z")
},
{
  "_id": ObjectId("602f5a11b5ff5e89d728c167"),
  "username": "bob",
  "email": "[email protected]",
  "lastLogin": ISODate("2022-02-22T08:15:33.000Z")
}

Now, we want to update alice’s lastLogin field to the current date. We can use the following code:

db.users.updateOne({ username: "alice" }, { $currentDate: { lastLogin: true } })

After running the above code, the users collection will become:

{
  "_id": ObjectId("602f5a00b5ff5e89d728c166"),
  "username": "alice",
  "email": "[email protected]",
  "lastLogin": ISODate("2023-03-09T05:42:58.000Z")
},
{
  "_id": ObjectId("602f5a11b5ff5e89d728c167"),
  "username": "bob",
  "email": "[email protected]",
  "lastLogin": ISODate("2022-02-22T08:15:33.000Z")
}

As you can see, alice’s lastLogin field has been updated to the current timestamp.

Conclusion

The $currentDate operator is a very useful tool that can automatically set a date field to the current date or time in an update operation.