Question

I’m a brand new developer so this might be a dumb question.

I am trying to setup a webapp which will store stats on geographic data.

• I have a model called Stat which has fields for basic statistical information (median, variance, avg, etc.).
• I have setup models for each geographic units City, Zip, Sub-Zip

What I want to do know is associate the Stat model with Cities, Zips, and Sub-Zips; that is every stat model belongs to either a city, zip, or sub-zip while a geographic unit (city,zip,sub-zip) can have multiple stats.

How do I setup the associations and migration to do this? I’ve looked through the Rails guides but it doesn’t seem to cover a relationship where an object can belong to different models (but only one of them). Or should I set up my models differently?

Answer 1

You said:

every stat model belongs to either a city, zip, or sub-zip while a
geographic unit (city,zip,sub-zip) can have multiple stats.

So I think you want to set up Polymorphic Associations:

With polymorphic associations, a model can belong to more than one
other model, on a single association.

So your association maybe like this:

class Stat
  belongs_to :statsable, polymorphic: true
end

class City
  has_many :stats, as: :statsable
end

class Zip
  has_many :stats, as: :statsable
end

class Subzip
  has_many :stats, as: :statsable
end