models.rb

class Author < ActiveRecord::Base
  has_one :history, as: :related
end

class History < ActiveRecord::Base
   belongs_to :related, polymorphic: true
 
   validates :related_id, presence: true, uniqueness: {scope: :related_type}
   validates :related_type, presence: true, uniqueness: true
end


# What i'd like to be able to do
a=Author.first

# Do this to unset the history -- stage it for deletion
a.history=nil

# Purges the history object at this point
a.save