How to make Rethink bulk "upsert" only by setting "createdDT" to insert (first update)?

Question

How to make Rethink bulk "upsert" only by setting "createdDT" to insert (first update)?

Is it possible to perform a massive upsert, which behaves so that a specific field (for example: createdDT ) is set only during the first update, but not during subsequent recreations of the same record?

EDIT

A rough version has been obtained that works with a server-side loop, where for each element, the result is a conditional insert. Not the most elegant and, most likely, quite effective way of taxation. Any other options?

 const tableName = "someTableName"; return r.expr(objs).forEach(function (docToInsert) { return r.table(tableName).get(docToInsert('id')).replace(function (existingDoc) { return r.branch( existingDoc.eq(null), r.expr(docToInsert).merge({ createdDT: r.now() }), existingDoc.merge(docToInsert) ); }); });