Question

I need to create a named scope in Mongoid that compares two Time fields within the same document. Such as

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

This obviously won’t work as it treats :checked_at as a symbol, not the actual field. Any suggestions on how this can be done?

Update 1

Here is my model where I have this scope declared, with a lot of extra 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 the following error:

'<class:User>': undefined method 'checked_at' for User:Class (NoMethodError)

Answer 1

As far as I know, mongodb doesn’t support queries against dynamic values.
But you could use a javascript function:

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

To speed this up you could add an attribute like “is_unresolved” which will be set to true on update when this condition is matched ( and index that ).