ruby on rails - Mongoid named scope comparing two time fields in the same document -

i need create named scope in mongoid compares 2 time fields within same document. such as

scope :foo, :where => {:updated_at.gt => :checked_at}

this won't work treats :checked_at symbol, not actual field. suggestions on how can done?

update 1

here model have scope declared, lot of code stripped out.

class user   include mongoid::document   include mongoid::paranoia   include mongoid::timestamps    field :checked_at, :type => time    scope :unresolved, :where => { :updated_at.gt => self.checked_at } end 

this gives me following error:

'<class:user>': undefined method 'checked_at' user:class (nomethoderror)

as far know, mongodb doesn't support queries against dynamic values. use javascript function:

scope :unresolved, :where => 'this.updated_at >= this.checked_at' 

to speed add attribute "is_unresolved" set true on update when condition matched ( , index ).