thanks, Uncle Cheese. I tried adding that:
...
$idom->setSourceID($this->owner->ID);
$idom->setParentClass('SiteConfig');
$fields->addFieldToTab("Root.Photos", $idom);
}
but still I receive
[User Error] Couldn't run query: SELECT "SlideshowPhoto"."ClassName", "SlideshowPhoto"."Created", "SlideshowPhoto"."LastEdited", "SlideshowPhoto"."Caption", "SlideshowPhoto"."ImageID", "SlideshowPhoto"."CustomSiteConfigID", "SlideshowPhoto"."ID", CASE WHEN "SlideshowPhoto"."ClassName" IS NOT NULL THEN "SlideshowPhoto"."ClassName" ELSE 'SlideshowPhoto' END AS "RecordClassName" FROM "SlideshowPhoto" WHERE ("ParentID" = '1') Unknown column 'ParentID' in 'where clause'