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  1. Core Server
  2. SERVER-6310

Timezone support in date operators at query time

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    • Backwards Compatibility:
      Fully Compatible
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      Description

      Issue Status as of July 26, 2017

      ISSUE SUMMARY

      In previous versions of MongoDB, the date extraction operations $year, $month, etc. could only extract the information from Date types in the UTC time zone. This meant that it was not possible to do grouping by date/time information in a local time zone. In versions 3.5.11 and newer, the date extraction operators ($year, $month, $day, $hour, $minute, $second, $millisecond, $isoYear, $isoWeekYear and $isoDayOfWeek) allow for a secondary format to specify a time zone to express a local time. This is accomplished with a new syntax in which the date operators accept an optional timezone argument in addition to the date argument:

      > db.c.aggregate({hour: {$hour: {date: '$lastUpdatedDate'}}})
      > db.c.aggregate({hour: {$hour: {date: '$lastUpdatedDate', timezone: 'Europe/Amsterdam'}}})
      

      This does not break backwards compatibility with existing applications. The original syntax of the operators is still functional:

      > db.c.aggregate({hour: {$hour: '$lastUpdatedDate'}})
      

      TECHNICAL DETAILS

      The implementation of time zone support is done through "timelib". Several formats for the timezone field are allowed:

      • An "Olson Time Zone Idenfitier": America/New_York, Europe/London, etc.
      • A string describing an ISO 8601 time zone specification: -05:00, +0445, -03, etc.
      • The strings Z, UTC and GMT.
      • Or an expression that evaluates to one of the above. This allows you to fetch the time zone information from a separate field in your document.

      ADDITIONAL CHANGES

      The $dateToString operator has also been updated (SERVER-28610), and the new operators $dateFromParts and $dateToParts (SERVER-28613), and $dateFromString (SERVER-29208, SERVER-29209) have been added, each also supporting time zones.

      Original description

      The date operators ($dayOfMonth, $dayOfWeek, $dayOfYear, $hour, $minute, $month, $week and $year) currently work for UTC. This causes the $group pipeline operator to insert certain rows in wrong bucket due to certain timezones being in another day.

      As an example, say you're showing website statistics for a US based company and at December 31st 2011 at 10:00 PM EST someone finally visits the website, if the aggregation framework didn't respect timezones (like it does now) it'd group the data point the next day (since it's stored as 2012-01-01T02:00:00Z). Which, if you're grouping data by year is quite the error as it would look like you'd have visitors from the future.

      Being able to set the timezone, either per query or per connection would solve this.

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