gistfile1.rb

# Tested with ActiveRecord 4.0.5
# Run using:
# BUNDLE_GEMFILE=gemfiles/rails_4.0.gemfile bundle console

require 'sqlite3'
require 'active_record'
require 'groupify/adapter/active_record'

ActiveSupport::VERSION::STRING
# => "4.0.5" 

ActiveRecord::Base.establish_connection( :adapter => 'sqlite3', :database => ":memory:" )

# Migrations
ActiveRecord::Schema.define(:version => 1) do
  create_table :groups do |t|
    t.string :name
    t.string :type

    t.timestamps
  end

  create_table :group_memberships do |t|
    t.string     :member_type
    t.integer    :member_id
    t.integer    :group_id
    t.string     :group_name
    t.string     :membership_type
  end

  create_table :users do |t|
    t.string :name
    t.string :type

    t.timestamps
  end
end

class User < ActiveRecord::Base
  acts_as_group_member
  acts_as_named_group_member
end

class Manager < User
end

class GroupMembership < ActiveRecord::Base
  acts_as_group_membership
end

class Group < ActiveRecord::Base
  acts_as_group :members => [:users], :default_members => :users
end

user = Manager.create!
# => #<Manager id: 1, name: nil, type: "Manager", created_at: "2014-08-21 09:03:58", updated_at: "2014-08-21 09:03:58"> 
group = Group.create!
# => #<Group id: 1, name: nil, type: nil, created_at: "2014-08-21 09:03:58", updated_at: "2014-08-21 09:03:58"> 
group.add(user, as: 'manager')
# => [#<Manager id: 1, name: nil, type: "Manager", created_at: "2014-08-21 09:03:58", updated_at: "2014-08-21 09:03:58">]