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$isoWeekYear (aggregation)

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Definition

$isoWeekYear

New in version 3.4.

Returns the year number in ISO 8601 format. The year starts with the Monday of week 1 and ends with the Sunday of the last week.

The $isoWeekYear expression has the following operator expression syntax:

{ $isoWeekYear: <dateExpression> }

Changed in version 3.6.

The argument must be a valid expression that resolves to one of the following:

  • A Date, a Timestamp, or an ObjectID.

  • A document of the following form:

    New in version 3.6.

    { 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 displayed 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

Example Result
{ $isoWeekYear: new Date("2015-05-26") }
2015
{ $isoWeekYear: { date: new Date("Jan 7, 2003") } }
2003
{ $isoWeekYear: ISODate("2017-01-02T00:00:00Z") }
2017
{ $isoWeekYear: {
    date: ISODate("2017-01-02T00:00:00Z"),
    timezone: "-0500"
} }
2016
{ $isoWeekYear: {
    date: new Date("April 08, 2024"),
    timezone: "America/Chicago"
} }
2024
{ $isoWeekYear: "March 28, 1976" }
error
{ $isoWeekYear: Date("2016-01-01") }
error
{ $isoWeekYear: "2009-04-09" }
error

Note

$isoWeekYear cannot take a string as an argument.

Example

A collection called anniversaries contains the following documents:

{ "_id" : 1, "date" : ISODate("2016-01-01T00:00:00Z") }
{ "_id" : 2, "date" : ISODate("2016-01-04T00:00:00Z") }
{ "_id" : 3, "date" : ISODate("2015-01-01T00:00:00Z") }
{ "_id" : 4, "date" : ISODate("2014-04-21T00:00:00Z") }

The following operation returns the year number in ISO 8601 format for each date field.

db.anniversaries.aggregate( [
  {
    $project: {
      yearNumber: { $isoWeekYear: "$date" }
    }
  }
] )

The operation returns the following results:

{ "_id" : 1, "yearNumber" : 2015 }
{ "_id" : 2, "yearNumber" : 2016 }
{ "_id" : 3, "yearNumber" : 2015 }
{ "_id" : 4, "yearNumber" : 2014 }