Docs Menu

Docs HomeDevelop ApplicationsMongoDB Manual

$month (aggregation)

On this page

  • Definition
  • Behavior
  • Example
$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 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"
Example
Result
{ $month: new Date("2016-01-01") }
1
{ $month: { date: new Date("Nov 7, 2003") } }
11
{ $month: ISODate("2000-01-01T00:00:00Z") }
1
{ $month: {
date: new Date("August 14, 2011"),
timezone: "America/Chicago"
} }
8
{ $month: {
date: ISODate("2000-01-01T00:00:00Z"),
timezone: "-0500"
} }
12
{ $month: "March 28, 1976" }
error
{ $month: {
date: Date("2016-01-01"),
timezone: "-0500"
} }
error
{ $month: "2009-04-09" }
error

Note

$month cannot take a string as an argument.

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
}
←  $mod (aggregation)$multiply (aggregation) →