(Rails) Various associations between otherwise unrelated entities?

Question

Hi All,

Ok, I've got a bit of an odd situation (as if none of my others were...). Basically I have a setup where there are 4 entities:

Sites -> Buildings -> Meters -> Values

I then have a fifth entity (Charts) that creates reports on the Values. I have a request to allow for Charts to be visually associated with any of those items in order to accommodate end users. Basically each chart can only be associated with any one entity at a time. Is there a quality "ACTS_AS" or something wild and crazy that will intuitively allow me to associate Charts with any and all entities without adding a table for each new association?

Best.

Answer 1

Perhaps you want polymorphic associations.

class Chart < ActiveRecord::Base
  # charts table has a chartable_id and a chartable_type column. Type is the 
  # class name of the associated chartable: Site, Building, etc.
  belongs_to :chartable, :polymorphic => true
end

class Site < ActiveRecord::Base
  has_one :chart, :as => :chartable
end

class Building < ActiveRecord::Base
  has_one :chart, :as => :chartable
end

# ...