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$dayOfMonth (aggregation)

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  • Definition
  • Behavior
  • Example
$dayOfMonth

Returns the day of the month for a date as a number between 1 and 31.

The $dayOfMonth expression has the following operator expression syntax:

{ $dayOfMonth: <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.

    Note
    Etc/ Timezones

    Etc/* timezones are supported starting in MongoDB 5.0.4. In earlier versions of MongoDB, use alternative timezone designations. For example, use UTC instead of Etc/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
{ $dayOfMonth: new Date("2016-01-01") }
1
{ $dayOfMonth: { date: new Date("Jan 7, 2003") } }
7
{ $dayOfMonth: {
date: new Date("August 14, 2011"),
timezone: "America/Chicago"
} }
14
{ $dayOfMonth: ISODate("1998-11-07T00:00:00Z") }
7
{ $dayOfMonth: {
date: ISODate("1998-11-07T00:00:00Z"),
timezone: "-0400"
} }
6
{ $dayOfMonth: "March 28, 1976" }
error
{ $dayOfMonth: Date("2016-01-01") }
error
{ $dayOfMonth: "2009-04-09" }
error
Note
$dayOfMonth 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 $dayOfMonth 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
}
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