Rails Single Table Inheritance Helper Module

Posted on March 12, 2012

Single table inheritance is a somewhat controversial topic in Rails land. For me, I like the Rails magic that it brings and, you know, the inheritance. However, it can clearly be abused. Here is my one rule for using Single table inheritance:

The models share the same data, but have differenct behavior.

I’ve created a helper module for use with Single Table Inheritance. The main advantage of this module is the factory method, with takes a type param and creates the correct object type.

module SingleTableInheritance
def self.included(klass)
klass.extend ClassMethods
end
def class_type=(value)
self[:type] = value
end
def class_type
return self[:type]
end
def after_initialize
self.class_type = self.name if self.class_type.nil?
end
def after_factory(params = {})
end
module ClassMethods
def factory(params = {})
class_name = params[:type] || params['type']
class_name ||= self.name
if defined? class_name.constantize
o = class_name.constantize.new(params)
else
o = self.new(params)
end
o.class_type = class_name if o.class_type.nil?
o.after_factory params
o
end
def factory!(params = {})
o = factory params
o.save!
o
end
def call_class_method(class_name, method_name, *args)
class_name ||= self.name
if defined? class_name.constantize
class_name.constantize.method(method_name).call(*args)
else
self.method(method_name).call(*args)
end
end
end
end
view raw single_table_inheritance.rb hosted with ❤ by GitHub

1 Reply to "Rails Single Table Inheritance Helper Module"

  • David
    March 27, 2012 (2:45 pm)
    Reply

    Hi Rebecca.. thanks for sharing your mind.. Can I ask you for a tiny example or tutorial of how to use your STI Helper Module in a Rails application?

    Cheers,
    David

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