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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:

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

The $dateToString takes a document with the following fields:

Field Description
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.
format

Optional. 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.

Changed in version 4.0: The format field is optional if featureCompatibilityVersion (fCV) is set to "4.0" or greater. For more information on fCV, see setFeatureCompatibilityVersion.
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
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"America/New_York"
"Europe/London"
"GMT"
UTC Offset
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+/-[hh]:[mm], e.g. "+04:45"
+/-[hh][mm], e.g. "-0530"
+/-[hh], e.g. "+03"
onNull

Optional. 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.

New in version 4.0: Requires featureCompatibilityVersion (fCV) set to "4.0" or greater. For more information on fCV, see setFeatureCompatibilityVersion.

See also

Format Specifiers

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

Specifiers Description Possible Values
%d Day of Month (2 digits, zero padded) 01-31
%G Year in ISO 8601 format 0000-9999
%H Hour (2 digits, zero padded, 24-hour clock) 00-23
%j Day of year (3 digits, zero padded) 001-366
%L Millisecond (3 digits, zero padded) 000-999
%m Month (2 digits, zero padded) 01-12
%M Minute (2 digits, zero padded) 00-59
%S Second (2 digits, zero padded) 00-60
%w Day of week (1-Sunday, 7-Saturday) 1-7
%u Day of week number in ISO 8601 format (1-Monday, 7-Sunday) 1-7
%U Week of year (2 digits, zero padded) 00-53
%V Week of Year in ISO 8601 format 01-53
%Y Year (4 digits, zero padded) 0000-9999
%z The timezone offset from UTC. +/-[hh][mm]
%Z The 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:

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{
  "_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:

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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:

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

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