ruby on rails - Atomic inc of multiple mongoid hash values -

i have mongoid model hash field looks this:

class dimensionstat  include ::mongoid::document  include ::mongoid::timestamps   field :data, type: hash   attr_accessible :data end 

i pretend on runtime fill data like

data: {     'a' => 1,     'b' => 2,     ... } 

i need perform increments on multiple keys atomically such as:

'a' => -1, 'b' => 5 

somewhere found that:

instance.collection.find(_id: my_id).update("$inc" => {'data.a' => -1, 'data.b' => 5}) 

will trick doesn't, doing wrong?

update: i'm using mongoid 3.1.6

the .inc method works non-existing keys, document not automatically refreshed database. try:

dimension_stat.inc('data.a' => -1, 'data.b' => 5) puts dimension_stat.data['a'] # not changed dimension_stat.reload puts dimension_stat.data['a'] # changed 

you see counters have changed.