Can nested attributes be used in combination with inheritance?

Question

I have the following classes:

• Project
• Person
• Person > Developer
• Person > Ma

Answer 1

I encountered a similar problem few days ago. The inheritance column(i.e. type) in a STI model is a protected attribute. Do the following to override the default protection in your Person class.

Rails 2.3

class Person < ActiveRecord::Base

private
  def attributes_protected_by_default
    super - [self.class.inheritance_column]
  end
end

Rails 3

Refer to the solution suggested by @tokland.

Caveat:

You are overriding the system protected attribute.

Reference:

SO Question on the topic

Answer 2

Patches above did not work for me, but this did (Rails3):

class ActiveRecord::Reflection::AssociationReflection
  def build_association(*options)
    if options.first.is_a?(Hash) and options.first[:type].presence
      options.first[:type].to_s.constantize.new(*options)
    else
      klass.new(*options)
    end
  end
end

Foo.bars.build(:type=>'Baz').class == Baz

Answer 3

Solution for Rails3: attributes_protected_by_default in now a class-method:

class Person < ActiveRecord::Base

  private

  def self.attributes_protected_by_default
    super - [inheritance_column]
  end
end

Answer 4

For those of us using Mongoid, you will need to make the _type field accessible:

class Person
  include Mongoid::Document
  attr_accessible :_type
end