module ActiveRecord::Associations::ForeignAssociation

def foreign_key_present?
  if reflection.klass.primary_key
    owner.attribute_present?(reflection.active_record_primary_key)
  else
    false
  end
end

def nullified_owner_attributes
  Hash.new.tap do |attrs|
    Array(reflection.foreign_key).each { |foreign_key| attrs[foreign_key] = nil }
    attrs[reflection.type] = nil if reflection.type.present?
  end
end

def set_owner_attributes(record)
  return if options[:through]
  primary_key_attribute_names = Array(reflection.join_primary_key)
  foreign_key_attribute_names = Array(reflection.join_foreign_key)
  primary_key_foreign_key_pairs = primary_key_attribute_names.zip(foreign_key_attribute_names)
  primary_key_foreign_key_pairs.each do |primary_key, foreign_key|
    value = owner._read_attribute(foreign_key)
    record._write_attribute(primary_key, value)
  end
  if reflection.type
    record._write_attribute(reflection.type, owner.class.polymorphic_name)
  end
end