$month (aggregation)

Definition

$month

Returns the month of a date as a number between 1 and 12.

The $month expression has the following operator expression syntax:

{ $month: <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

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

{ $month: { date: new Date("Nov 7, 2003") } }

{ $month: ISODate("2000-01-01T00:00:00Z") }

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

{ $month: {
    date: ISODate("2000-01-01T00:00:00Z"),
    timezone: "-0500"
} }

{ $month: "March 28, 1976" }

{ $month: {
    date: Date("2016-01-01"),
    timezone: "-0500"
} }

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

Example

Consider a sales collection with the following document:

{
  "_id" : 1,
  "item" : "abc",
  "price" : 10,
  "quantity" : 2,
  "date" : ISODate("2014-01-01T08:15:39.736Z")
}

The following aggregation uses the $month and other date operators to break down the date field:

db.sales.aggregate(
   [
     {
       $project:
         {
           year: { $year: "$date" },
           month: { $month: "$date" },
           day: { $dayOfMonth: "$date" },
           hour: { $hour: "$date" },
           minutes: { $minute: "$date" },
           seconds: { $second: "$date" },
           milliseconds: { $millisecond: "$date" },
           dayOfYear: { $dayOfYear: "$date" },
           dayOfWeek: { $dayOfWeek: "$date" },
           week: { $week: "$date" }
         }
     }
   ]
)

The operation returns the following result:

{
  "_id" : 1,
  "year" : 2014,
  "month" : 1,
  "day" : 1,
  "hour" : 8,
  "minutes" : 15,
  "seconds" : 39,
  "milliseconds" : 736,
  "dayOfYear" : 1,
  "dayOfWeek" : 4,
  "week" : 0
}