[{"fieldA":"value","fieldB":"value","fieldC":"value","fieldD":"value","fieldE":"value","specialField":"value"},{"fieldC":"value","fieldE":"value","fieldB":"value","fieldD":"value","fieldA":"value"},{"fieldE":"value","fieldA":"value","fieldD":"value","fieldB":"value","fieldC":"value"}]

db.collection.aggregate([{$replaceWith:{$mergeObjects:[{"_id":"$_id","fieldA":"$fieldA","fieldB":"$fieldB","fieldC":"$fieldC","fieldD":"$fieldD","fieldE":"$fieldE"},"$$ROOT"]}}])