ActiveRecord::MTI

ActiveRecord support for PostgreSQL's native inherited tables (multi-table inheritance)

Compatible with ActiveRecord 4.0, 4.1, 4.2, 5.0, 5.1

Confirmed production use in 4.2

Usage

Add this line to your application's Gemfile:

gem 'active_record-mti'

And then execute:

$ bundle

Or install it yourself as:

$ gem install active_record-mti

Application Code

In most cases, you shouldn't have to do anything beyond installing the gem. ActiveRecord::MTI will do it's best to determine the nature of inheritance in your models. If your models map to their own tables, ActiveRecord::MTI will step in and make sure inheritance is treated appropriately. Otherwise it will gracefully aquiece to ActiveRecord's built-in STI.

class Account < ::ActiveRecord::Base
  # ...
end

class User < Account
  # ...
end

class Developer < Account
  # ...
end

ActiveRecord queries work as usual with the following differences:

• The default query of "*" is changed to include the OID of each row for subclass discrimination. The default select will be SELECT "accounts"."tableoid" AS tableoid, "accounts".* (for example)

Note

Migrations

In your migrations define a table to inherit from another table:

class CreateAccounts < ActiveRecord::Migration
  def change
    create_table :accounts do |t|
      t.jsonb      :settings
      t.timestamps null: false
    end

    create_table :users, inherits: :accounts do |t|
      t.string     :firstname
      t.string     :lastname
    end

    create_table :developers, inherits: :users do |t|
      t.string     :url
      t.string     :api_key
    end
  end
end

Schema

A schema will be created that reflects the inheritance chain so that rake:db:schema:load will work

ActiveRecord::Schema.define(version: 20160910024954) do

  create_table "accounts", force: :cascade do |t|
    t.jsonb    "settings"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
  end

  create_table "users", inherits: "accounts" do |t|
    t.string "firstname"
    t.string "lastname"
  end

  create_table "developers", inherits: "users" do |t|
    t.string "url"
    t.string "api_key"
  end

end

Contributing

1. Fork it ( https://github.com/[my-github-username]/active_record-mti/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request