php - MongoDate aggregation with timezone correction -

i generating report of orders broken down date, month , year using aggregate group function. date stored in mongodate object in utc.

'$group' => array (     '_id' => array (          'year' => array ( '$year' => '$created' ),         'month' => array ( '$month' => '$created' ),         'day' => array ( '$dayofmonth' => '$created' ),      ) ) 

i have tried adding date object using project, seems cannot add mongodate object. (as seen here: https://stackoverflow.com/a/18854229/1069277)

'$project' => array (      'created' => array (          '$add' => array (              '$created' => 8 * 60 * 60 * 1000          )      )  ) 

is adding field stores timezone corrected way achieve @ moment?

i go on using date operators aggregation , doing date math in order change timestamp value (which referenced answer doing, not bson date) lengthy , inefficient.

what want do conversion in code , pass in mongodate type.

here's round-trip code consider:

date_default_timezone_set('utc');  $dt = new datetime("2014-02-01", new datetimezone('pst')); echo var_dump( $dt );  echo $dt->gettimestamp(), "\n";  $mongo = new mongodate( $dt->gettimestamp() );  echo var_dump( $mongo );  echo $mongo->sec, "\n";  $new = new datetime( date('y-m-d', $mongo->sec ), new datetimezone('pst'));  echo var_dump ($new); 

so whether passing in values or working results, conversions in code. it's better way.