This article presents 5 ways to return the seconds portion from a Date object in MongoDB.

Sample Data

Suppose we have a collection called cats with the following documents:

{ "_id" : 1, "name" : "Scratch", "born" : ISODate("2021-01-03T23:30:15.123Z") }
{ "_id" : 2, "name" : "Meow", "born" : ISODate("2019-12-08T04:00:20.112Z") }
{ "_id" : 3, "name" : "Fluffy", "born" : ISODate("2020-09-24T10:45:01.007Z") }

The following examples demonstrate various options for returning the seconds portion from the born field of those documents.

The $second Operator

The $second operator is designed specifically to return a document with the seconds portion of a given date.

We can run the following code to return the seconds portion from the born field in the above document.

db.cats.aggregate(
  [
    {
      $project:
        {
          _id: 0,
          birthSecond: { $second: "$born" }
        }
    }
  ]
)

Result:

{ "birthSecond" : 15 }
{ "birthSecond" : 20 }
{ "birthSecond" : 1 }

You can also specify the timezone when using the $second operator.

See MongoDB $second for more information and examples.

The $dateToString Operator

The $dateToString operator converts a date object to a string according to a user-specified format. The user can therefore specify that just the seconds portion is returned if required.

There are format specifiers for each date part. The %S format specifier returns the second portion  (2 digits, zero padded).

Example:

db.cats.aggregate(
   [
     {
       $project: {
         _id: 0,
          birthSecond: { $dateToString: { format: "%S", date: "$born" } }
       }
     }
   ]
)

Result:

{ "birthSecond" : "15" }
{ "birthSecond" : "20" }
{ "birthSecond" : "01" }

See MongoDB $dateToString for more information and examples.

The $dateToParts Operator

The $dateToParts operator returns a document that contains the constituent parts of a given BSON Date value as individual properties. The properties returned are year, month, day, hour, minute, second and millisecond.

We could therefore use $dateToParts in one pipeline stage, then add another pipeline stage that extracts the second part.

Here’s what $dateToParts returns for our three documents:

db.cats.aggregate(
  [
    {
      $project:
        {
          _id: 0,
          dateParts: { $dateToParts: { date: "$born" } }
        }
    }
  ]
).pretty()

Result:

{
	"dateParts" : {
		"year" : 2021,
		"month" : 1,
		"day" : 3,
		"hour" : 23,
		"minute" : 30,
		"second" : 15,
		"millisecond" : 123
	}
}
{
	"dateParts" : {
		"year" : 2019,
		"month" : 12,
		"day" : 8,
		"hour" : 4,
		"minute" : 0,
		"second" : 20,
		"millisecond" : 112
	}
}
{
	"dateParts" : {
		"year" : 2020,
		"month" : 9,
		"day" : 24,
		"hour" : 10,
		"minute" : 45,
		"second" : 1,
		"millisecond" : 7
	}
}

This result can then be passed to the next stage in the pipeline, and we can therefore extract just the second field in the next stage.

Here’s what happens if we add another projection for just the second field:

db.cats.aggregate(
  [
    {
      $project:
        {
          _id: 0,
          dateParts: { $dateToParts: { date: "$born" } }
        }
    },
    {
      $project:
        {
          birthSecond: "$dateParts.second"
        }
    }
  ]
)

Result:

{ "birthSecond" : 15 }
{ "birthSecond" : 20 }
{ "birthSecond" : 1 }

So, whenever you use $dateToParts in your pipeline, you will have access to the second field (and the other date parts) in the next stage.

See MongoDB $dateToParts for more information and examples.

The forEach() Method

You can use cursor.forEach() to iterate through the cursor, using a JavaScript method such as getSeconds() or getUTCSeconds() to return just the seconds.

db.cats.find().forEach(
  function(c) {
    print(
      c.born.getUTCSeconds()
      );
  }
);

Result:

15
20
1

The getUTCSeconds() JavaScript method returns an integer number, between 0 and 59, representing the seconds in the given date according to universal time.

The getSeconds() method returns it in local time.

You may also notice that the previous options return a whole document that contains a name/value pair, whereas this option returns just the actual seconds value, and not the whole document.

The map() Method

The cursor.map() method applies a function to each document visited by the cursor and combines the values into an array.

Example:

db.cats.find().map(
  function(c) {
    c = c.born.getUTCSeconds();
    return c;
  }
);

Result:

[ 15, 20, 1 ]