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$dateToString (aggregation)

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Definition

$dateToString

Converts a date object to a string according to a user-specified format.

The $dateToString expression has the following operator expression syntax:

{ $dateToString: {
    date: <dateExpression>,
    format: <formatString>,
    timezone: <tzExpression>,
    onNull: <expression>
} }

The $dateToString takes a document with the following fields:

FieldDescription
date
Changed in version 3.6.
The date to convert to string. <dateExpression> must be a valid expression that resolves to a Date, a Timestamp, or an ObjectID.
formatOptional. The date format specification. <formatString> can be any string literal, containing 0 or more format specifiers. For a list of specifiers available, see Format Specifiers.
If unspecified, $dateToString uses "%Y-%m-%dT%H:%M:%S.%LZ" as the default format.
timezoneOptional. 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.
FormatExamples
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"
onNullOptional. The value to return if the date is null or missing. The arguments can be any valid expression.
If unspecified, $dateToString returns null if the date is null or missing.

Tip

See also:

Format Specifiers

The following format specifiers are available for use in the <formatString>:

SpecifiersDescriptionPossible Values
%bAbbreviated month (3 letters)jan-dec
%BFull month namejanuary-december
%dDay of month (2 digits, zero padded)01-31
%GYear in ISO 8601 format0000-9999
%HHour (2 digits, zero padded, 24-hour clock)00-23
%jDay of year (3 digits, zero padded)001-366
%LMillisecond (3 digits, zero padded)000-999
%mMonth (2 digits, zero padded)01-12
%MMinute (2 digits, zero padded)00-59
%SSecond (2 digits, zero padded)00-60
%uDay of week number in ISO 8601 format (1-Monday, 7-Sunday)1-7
%UWeek of year (2 digits, zero padded)00-53
%VWeek of Year in ISO 8601 format01-53
%wDay of week (0-Sunday, 6-Saturday)0-6
%YYear (4 digits, zero padded)0000-9999
%zThe timezone offset from UTC.+/-[hh][mm]
%ZThe minutes offset from UTC as a number. For example, if the timezone offset (+/-[hhmm]) was +0445, the minutes offset is +285.+/-mmm
%%Percent Character as a Literal%

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 $dateToString to return the date field as formatted strings:

db.sales.aggregate(
   [
     {
       $project: {
          yearMonthDayUTC: { $dateToString: { format: "%Y-%m-%d", date: "$date" } },
          timewithOffsetNY: { $dateToString: { format: "%H:%M:%S:%L%z", date: "$date", timezone: "America/New_York"} },
          timewithOffset430: { $dateToString: { format: "%H:%M:%S:%L%z", date: "$date", timezone: "+04:30" } },
          minutesOffsetNY: { $dateToString: { format: "%Z", date: "$date", timezone: "America/New_York" } },
          minutesOffset430: { $dateToString: { format: "%Z", date: "$date", timezone: "+04:30" } }
       }
     }
   ]
)

The operation returns the following result:

{
   "_id" : 1,
   "yearMonthDayUTC" : "2014-01-01",
   "timewithOffsetNY" : "03:15:39:736-0500",
   "timewithOffset430" : "12:45:39:736+0430",
   "minutesOffsetNY" : "-300",
   "minutesOffset430" : "270"
}