Acts As Realation

Easy multi-table inheritance for rails. With acts_as_relation models inherit parent model:

• columns
• validations
• methods

Multi-table inheritance

Multi-table inheritance happens when each model in the hierarchy is a model all by itself that corresponds to its own database table and can be queried and created individually. The inheritance relationship introduces links between the child model and each of its parents (via an automatically-created has_one associations).

Example

generate models

$ rails g model product name:string price:float
$ rails g model pen color:string

Add next option to Product Migration:

create_table :products, :as_relation_superclass => true

add some validations and instance methods

class Product < ActiveRecord::Base
  validates_presence_of :name, :price

  def hello
    puts "Hello, My name is '#{name}', my price is $#{price}."
  end
end

product is superclass for all kind of products:

class Product < ActiveRecord::Base
  acts_as_superclass
end

pen inherits from product

class Pen < ActiveRecord::Base
  acts_as :product
end

to get some specific class(as example: specific product - Pen) from superclass can be used method specific_class:

Pen.create :name => 'Pen A', :color=> 'black', :price => 0.42
product = Product.first
product.specific_class # will be instance of Pen class

to get name of association used between superclass and children can be used method acts_as_association_name:

Product.acts_as_association_name # 'Productable'

after deleting specific object will be removed linked superobject:

Pen.first.destroy # delete as Pen row as linked Product row

pen inherits products validations and columns

p = Pen.new
p.valid? => false
p.errors => {:name=>["can't be blank"], :price=>["can't be blank"]}

pen inherits product methods

pen = Pen.new(:name=>"Red Pen", :color=>:red, :price=>0.99)
pen.hello => Hello, My name is 'Red Pen', my price is $0.99.

we can make queries on both models

Product.where("price <= 1")
Pen.where("color = ?", color)

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Copyright (c) 2011 Hassan Zamani, released under the MIT license.