$m->demo->steps->update(
        [ 'person' => "derickr" ],
        [ '$inc' => [ "steps_made.20140202" => 712 ] ],
        [ 'upsert' => true ]
);
Record after update:


{
        person: "derickr",
        steps_made: {
                "20140201": 10800,
                "20140202": 712,
        }
}