module ActiveRecord::Inheritance

No such attribute would be set for objects of the Message class in that example.
do Reply.new without having to set Reply[Reply.inheritance_column] = "Reply" yourself.
Considering the hierarchy Reply < Message < ActiveRecord::Base, this makes it possible to
ActiveRecord::Base descendant.
Sets the attribute used for single table inheritance to this class name if this is not the

def ensure_proper_type
  klass = self.class
  if klass.finder_needs_type_condition?
    _write_attribute(klass.inheritance_column, klass.sti_name)
  end
end

def initialize_dup(other)
  super
  ensure_proper_type
end

def initialize_internals_callback
  super
  ensure_proper_type
end