select related_object_id as correction_file_id from cr_item_rels where item_id = :file_id and relation_tag = 'homework_correction' update acs_objects set context_id = null where object_id = :file_id update acs_objects set context_id = null where object_id = :correction_file_id select name from cr_items where item_id = :file_id select count(*) from cr_items where name = :filename and parent_id = :parent_id