Today, I would like to show you an improved way to manage Single Table Inheritance with ActiveScaffold. It s a real time safer.
STI Models should hopefully have a big overlap of attributes, which is the base assumption for my implementation of STI in ActiveScaffold.

Basically, we will show an index view of parent sti controller, in which member actions such as edit, show,delete are linking to corresponding specific sti controller. Create link opens a popup menu showing the different sti models.

That s the concept let s try it out. I will use an example from the book: “Agile Web Development with Rails” written by Dave Thomas and David Heinemeier Hansson.
That example consist of the following models:

  1. Person (sti_parent)
  2. Customer
  3. Employee (Parent of Manager)
  4. Manager

It s quite tedious to set up an application with these models, therefore we will shorten that process.

Setup Example Application

  1. Download: one_step_active_scaffold
  2. Download: sti_blog.rb and rename it to model_setup.rb
  3. Execute following command: ruby one_step_activescaffold.rb sti jquery

Great, we ve prepared our example application, now we have to configure our controllers

Controller Inheritance

ActiveScaffold configuration can be inherited, which is quite useful for sti, because many columns are shared.

class CustomersController < PeopleController

class EmployeesController < PeopleController

class ManagersController < EmployeesController

Definition of column set for each Controller

We have to define for each controller, which columns we would like to use. Please note that we do not have to define anything specific for manager controller because it should use same settings as employee controller.

class PeopleController < ApplicationController
  active_scaffold :person do |conf|
    conf.columns = [:type, :name, :email]
  end
end 

class CustomersController < PeopleController
  active_scaffold :customer do |conf|
    conf.columns = [:type, :name, :email, :balance]
    conf.update.columns = [:name, :email, :balance]
    conf.create.columns = [:name, :email, :balance]
  end
end

class EmployeesController < PeopleController
  active_scaffold :employee do |conf|
     conf.columns = [:type, :name, :email, :boss, :department]
     conf.update.columns = [:name, :email, :boss, :department]
     conf.create.columns = [:name, :email, :boss, :department]
  end
end

Parent Controller STI Child Models

One last step, we have to tell the parent controller, which sti_models he should be able to manage.

class PeopleController < ApplicationController
  active_scaffold :person do |conf|
    ....
    conf.sti_children = [:employee, :customer, :manager]
    ....
  end

Our Application is ready, start the server and go to: localhost:3000/people.

Hopefully, you will benefit as much as I did.

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