def get_ref_data_map(self, bulk_mode=True):
        """
        Get referential data from the local db into the self.ref_data_map dictionary.
        This allows for fast FK lookups when looping through posts.

        :param bulk_mode: if True, actually get all of the existing ref data
                          else this would be too much memory, so just build empty dicts
        :return: None
        """
        if bulk_mode:
            self.ref_data_map = {
                "authors": {a.wp_id: a for a in Author.objects.filter(site_id=self.site_id)},
                "categories": {c.wp_id: c for c in Category.objects.filter(site_id=self.site_id)},
                "tags": {t.wp_id: t for t in Tag.objects.filter(site_id=self.site_id)},
                "media": {m.wp_id: m for m in Media.objects.filter(site_id=self.site_id)}
            }
        else:
            # in single post mode, WP ref data is handled dynamically for the post
            self.ref_data_map = {
                "authors": {},
                "categories": {},
                "tags": {},
                "media": {}
            }
Get referential data from the local db into the self.ref_data_map dictionary.
        This allows for fast FK lookups when looping through posts.

        :param bulk_mode: if True, actually get all of the existing ref data
                          else this would be too much memory, so just build empty dicts
        :return: None