assign_nested_attributes_for_one_to_one_association method definition

gistfile1.rb

# File activerecord/lib/active_record/nested_attributes.rb, line 289
    def assign_nested_attributes_for_one_to_one_association(association_name, attributes)
      options = nested_attributes_options[association_name]
      attributes = attributes.with_indifferent_access
      check_existing_record = (options[:update_only] || !attributes['id'].blank?)

      if check_existing_record && (record = send(association_name)) &&
          (options[:update_only] || record.id.to_s == attributes['id'].to_s)
        assign_to_or_mark_for_destruction(record, attributes, options[:allow_destroy]) unless call_reject_if(association_name, attributes)

      elsif !attributes['id'].blank?
        raise_nested_attributes_record_not_found(association_name, attributes['id'])

      elsif !reject_new_record?(association_name, attributes)
        method = "build_#{association_name}"
        if respond_to?(method)
          send(method, attributes.except(*UNASSIGNABLE_KEYS))
        else
          raise ArgumentError, "Cannot build association #{association_name}. Are you trying to build a polymorphic one-to-one association?"
        end
      end
    end