Documentation Request Summary:
Aggregation date expressions will accept input of type ObjectId.
Engineering Ticket Description:
Since ObjectId() encompasses an approximation of insertion date it would be helpful if _id/things of ObjectId() type could be operated/projected the same way as Datetime type object.
{case}
{$project:{$year:"$_id"}} would extract year out of ObjectId().getTimestamp equivalent.{case}
One question would be whether ObjectId could be operated on directly via date/interval arithmetic. I.e. whether it can be used anywhere a date can be used returning a standard Datetime type as a result from say {$subtract:["$_id",86400000]} which can only return ts of one day before that ObjectId's timestamp.
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