$isoDayOfWeek (expression operator)

Definition

$isoDayOfWeek

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

The $isoDayOfWeek expression has the following operator expression syntax:

{ $isoDayOfWeek: <dateExpression> }

The argument can be:

• An expression that resolves to a Date, a Timestamp, or an ObjectID.

• A document with this format:

  { date: <dateExpression>, timezone: <tzExpression> }

  Field	Description
  date	The date to which the operator is applied. <dateExpression> must be a valid expression that resolves to a Date, a Timestamp, or an ObjectID.
  timezone	Optional. The timezone of the operation result. <tzExpression> must be a valid expression that resolves to a string formatted as either an Olson Timezone Identifier or a UTC Offset. If no timezone is provided, the result is in UTC. Format Examples Olson Timezone Identifier "America/New_York" "Europe/London" "GMT" UTC Offset +/-[hh]:[mm], e.g. "+04:45" +/-[hh][mm], e.g. "-0530" +/-[hh], e.g. "+03"

Behavior

{ $isoDayOfWeek: new Date("2016-01-01") }

{ $isoDayOfWeek: { date: new Date("Jan 7, 2003") } }

{ $isoDayOfWeek: {
    date: new Date("August 14, 2011"),
    timezone: "America/Chicago"
} }

{ $isoDayOfWeek: ISODate("1998-11-07T00:00:00Z") }

{ $isoDayOfWeek: {
    date: ISODate("1998-11-07T00:00:00Z"),
    timezone: "-0400"
} }

{ $isoDayOfWeek: "March 28, 1976" }

{ $isoDayOfWeek: Date("2016-01-01") }

{ $isoDayOfWeek: "2009-04-09" }

Example

A collection called birthdays contains the following documents:

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

The operation returns the following results:

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