Polymorphic associations in Ruby on Rails allow you to have a model associated with more than one other model without the use of a join table.

This works by adding type and id field to the table of the model you wish to make polymorphic.

rails g model Person first_name last_name
rails g model Business name
rails g model Interaction description interactive:references{polymorphic}

rake db:migrate
rails server

For example, lets say we have 3 models. The first 2 models, Business and Person, each can have interactions associated with them.

These interactions share the same business logic regardless of the associated model so we can easily make interactions polymorphic.

The third model, Interaction, will store simple descriptions of various phone calls and other interactions that the user has had.

# app/models/person.rb:
class Person < ActiveRecord::Base
  has_many :interactions, as: :interactive
end

#app/models/business.rb:
class Business < ActiveRecord::Base
  has_many :interactions, as: :interactive
end

#app/models/business.rb:
class Interaction < ActiveRecord::Base
  belongs_to :interactive, polymorphic: true
end

To test check the rails console

rails console
Interaction.column_names

Now if we open up a rails console using the rails console command notice that there are two columns, interactive_id, and interactive_type. The interactive_type column holds the type of the model that the interaction belongs to. The interactive_id holds the id of the model that the interaction belongs to.

Now create all 3 controllers:

The final controller, Interactions, will handle the saving of each interaction.

rails g controller People index show new create edit update
rails g controller Businesses index show new create edit update
rails g controller Interactions new create edit update

Then add all controller code to each view...

mv README.rdoc README.md
bundle exec erd
open erd.pdf # to see a visual 

Either screenshot or save .pdf as .png

Move it to assets folder

Add it to your README.md