<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def action_add(self):
 """Form action to add a new attachment Code taken from bika.lims.content.addARAttachment. """


        form = self.request.form
        parent = api.get_parent(self.context)
        attachment_file = form.get('AttachmentFile_file', None)
        AttachmentType = form.get('AttachmentType', '')
        AttachmentKeys = form.get('AttachmentKeys', '')
        ReportOption = form.get('ReportOption', 'r')

        # nothing to do if the attachment file is missing
        if attachment_file is None:
            logger.warn("AttachmentView.action_add_attachment: Attachment file is missing")
            return

        # create attachment
        attachment = self.create_attachment(
            parent,
            attachment_file,
            AttachmentType=AttachmentType,
            AttachmentKeys=AttachmentKeys,
            ReportOption=ReportOption)

        # append the new UID to the end of the current order
        self.set_attachments_order(api.get_uid(attachment))

        # handle analysis attachment
        analysis_uid = form.get("Analysis", None)
        if analysis_uid:
            analysis = api.get_object_by_uid(analysis_uid)
            others = analysis.getAttachment()
            attachments = []
            for other in others:
                attachments.append(other.UID())
            attachments.append(attachment.UID())
            analysis.setAttachment(attachments)
            # The metadata for getAttachmentUIDs need to get updated,
            # otherwise the attachments are not displayed
            # https://github.com/senaite/bika.lims/issues/521
            analysis.reindexObject()

        else:
            others = self.context.getAttachment()
            attachments = []
            for other in others:
                attachments.append(other.UID())
            attachments.append(attachment.UID())

            self.context.setAttachment(attachments)

        if self.request['HTTP_REFERER'].endswith('manage_results'):
            self.request.response.redirect('{}/manage_results'.format(
                self.context.absolute_url()))
        else:
            self.request.response.redirect(self.context.absolute_url())