class ActiveRecord::Associations::CollectionAssociation

def concat_records(records, raise = false)
  result = true
  records.each do |record|
    raise_on_type_mismatch!(record)
    add_to_target(record) do
      unless owner.new_record?
        result &&= insert_record(record, true, raise) {
          @_was_loaded = loaded?
        }
      end
    end
  end
  raise ActiveRecord::Rollback unless result
  records
end