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This is a refactor of acts_as_relation

Simulates multiple-table-inheritance (MTI) for ActiveRecord models. By default, ActiveRecord only supports single-table inheritance (STI). MTI gives you the benefits of STI but without having to place dozens of empty fields into a single table.

Take a traditional e-commerce application for example: A product has common attributes (name, price, image ...), while each type of product has its own attributes: for example a pen has color, a book has author and publisher and so on. With multiple-table-inheritance you can have a products table with common columns and a separate table for each product type, i.e. a pens table with color column.


AciveRecord ~> 4.1.2 or newest


Add this line to your application's Gemfile:

gem 'active_record-acts_as'

And then execute:

$ bundle

Or install it yourself as:

$ gem install active_record-acts_as


Back to example above, all you have to do is to mark Product as actable and all product type models as acts_as :product:

class Product < ActiveRecord::Base
  belongs_to :store

  validates_presence_of :name, :price

  def info
    "#{name} $#{price}"

class Pen < ActiveRecord::Base
  acts_as :product

class Book < ActiveRecord::Base
  # In case you don't wish to validate
  # this model against Product
  acts_as :product, validates_actable: false

class Store < ActiveRecord::Base
  has_many :products

and add foreign key and type columns to products table as in a polymorphic relation. You may prefer using a migration:

change_table :products do |t|
  t.integer :actable_id
  t.string  :actable_type

or use shortcut actable

change_table :products do |t|

Make sure that column names do not match on parent and subclass tables, that will make SQL statements ambiguous and invalid! Specially DO NOT use timestamps on subclasses, if you need them define them on parent table and they will be touched after submodel updates.

Now Pen and Book acts as Product, i.e. they inherit Products attributes, methods and validations. Now you can do things like these:

Pen.create name: 'Penie!', price: 0.8, color: 'red'
  # => #<Pen id: 1, color: "red">
Pen.where price: 0.8
  # => [#<Pen id: 1, color: "red">]
pen = Pen.where(name: 'new pen', color: 'black').first_or_initialize
  # => #<Pen id: nil, color: "black">
  # => "new pen"
Product.where price: 0.8
  # => [#<Product id: 1, name: "Penie!", price: 0.8, store_id: nil, actable_id: 1, actable_type: "Pen">]
pen =
  # => false
  # => ["Name can't be blank", "Price can't be blank", "Color can't be blank"]
  # => "Penie! $0.8"

On the other hand you can always access a specific object from its parent by calling specific method on it:

  # => #<Pen ...>

If you have to come back to the parent object from the specific, the acting_as returns the parent element:

  # => #<Product ...>

In has_many case you can use subclasses:

store = Store.create
store.products << Pen.create
  # => #<Product: ...>

You can give a name to all methods in :as option:

class Product < ActiveRecord::Base
  actable as: :producible

class Pen < ActiveRecord::Base
  acts_as :product, as: :producible

change_table :products do |t|
  t.actable as: :producible

acts_as support all has_one options, where defaults are there: as: :actable, dependent: :destroy, validate: false, autosave: true

Make sure you know what you are doing when overwriting validate or autosave options.

You can pass scope to acts_as as in has_one:

acts_as :person, -> { includes(:friends) }

actable support all belongs_to options, where defaults are these: polymorphic: true, dependent: :delete, autosave: true

Make sure you know what you are doing when overwriting polymorphic option.

Migrating from acts_as_relation

Replace acts_as_superclass in models with actable and if you where using :as_relation_superclass option on create_table remove it and use t.actable on column definitions.

RSpec custom matchers

To use this library custom RSpec matchers, you must require the rspec/acts_as_matchers file.


require "active_record/acts_as/matchers"

RSpec.describe "Pen acts like a Product" do
  it { act_as(:product) }
  it { act_as(Product) }

  it { expect(Person).to act_as(:product) }
  it { expect(Person).to act_as(Product) }

RSpec.describe "Product is actable" do
  it { expect(Product).to be_actable }


  1. Fork it ( )
  3. Test changes don't break anything (rspec)
  4. Add specs for your new feature
  7. Create a new Pull Request