def DATE_TO_STRING(_format, date):
return {'<STR_LIT>': {'<STR_LIT>': _format, '<STR_LIT:date>': date}}<EOL>
Converts a date object to a string according to a user-specified format.
See https://docs.mongodb.com/manual/reference/operator/aggregation/dateToString/
for more details
:param _format: The date format specification.
:param date: expression or variable of a Date, a Timestamp, or an ObjectID
:return: Aggregation operator