How to upsert a single mongodb field using the ruby 2 driver

Pontifications

where upsert means add it if not present, update if present

From add-answered-in-72-hours.rb an example of how to upsert a boolean, answered_in_72_hours:

questionsColl.find_one_and_update(
    { id: q["id"] }, { "$set" => { answered_in_72_hours: answered_in_72_hours }},
    :upsert => true)