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$isoDayOfWeek (aggregation)

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Definition

$isoDayOfWeek

New in version 3.4.

Returns the weekday number in ISO 8601 format, ranging from 1 (for Monday) to 7 (for Sunday).

$isoDayOfWeek has the following operator expression syntax:

{ $isoDayOfWeek: <date expression> }

The argument can be any valid expression that resolves to a BSON ISODate object, a BSON Timestamp object, or a Date object.

Behavior

Example Result
{ $isoDayOfWeek: new Date("2016-01-01") } 5
{ $isoDayOfWeek: new Date("Jan 7, 2003") } 2
{ $isoDayOfWeek: new Date("August 14, 2011") } 7
{ $isoDayOfWeek: ISODate("1998-11-07T00:00:00Z") } 6
{ $isoDayOfWeek: "March 28, 1976" } error
{ $isoDayOfWeek: "2009-04-09" } error

Note

$isoDayOfWeek cannot take a string as an argument.

Example

A collection called birthdays contains the following documents:

{ "_id" : 1, "name" : "Betty", "birthday" : ISODate("1993-09-21T00:00:00Z") }
{ "_id" : 2, "name" : "Veronica", "birthday" : ISODate("1981-11-07T00:00:00Z") }

The following operation returns the weekday number for each birthday field.

db.dates.aggregate( [
  {
    $project: {
      _id: 0,
      name: "$name",
      dayOfWeek: { $isoDayOfWeek: "$birthday" }
    }
  }
] )

The operation returns the following results:

{ "name" : "Betty", "dayOfWeek" : 2 }
{ "name" : "Veronica", "dayOfWeek" : 6 }