Implementando STI - Single Table Inheritance

gistfile1.txt

Neste exemplo eu utilizarei State, City e Upload para ser os models associados. 

Mostro logo abaixo um passo a passo como implementar.

1 - Gerar as migrations
## State 
class CreateStates < ActiveRecord::Migration[5.0]
  def change
    create_table :states do |t|
      t.string  :name
      t.timestamps
    end
  end
end

## City 
class CreateCities < ActiveRecord::Migration[5.0]
  def change
    create_table :cities do |t|
      t.string :name
      t.timestamps
    end
  end
end

## Upload
class CreateUploads < ActiveRecord::Migration[5.0]
  def change
    create_table :uploads do |t|
      t.string :picture
      t.integer :modelable_id
      t.string :modelable_type

      t.timestamps
    end
    
    add_index :uploads, [:modelable_type, :modelable_id]
  end
end

2 - criar as associações entre os models

  ## 1ª model - State
  class State < ApplicationRecord
    # association
    has_many :uploads,  as: :modelable, inverse_of: :modelable
  end 

  ## 2ª model - City
  class State < ApplicationRecord
    # association
    has_many :uploads,  as: :modelable, inverse_of: :modelable
  end 

  ## 3ª model - Upload
  class State < ApplicationRecord
    # associations
    belongs_to :modelable, polymorphic: true
  end