modify sql functions

sql/set_folder_path.sql

@@ -1,4 +1,6 @@
-CREATE OR REPLACE PROCEDURE set_folder_path(in_url text) AS $$
+CREATE OR REPLACE FUNCTION public.set_folder_path(in_url text) RETURNS integer
+	LANGUAGE plpgsql STRICT
+	AS $$
 DECLARE
 	temp_folder_path text;
 	aw_artist_id integer;
@@ -9,18 +11,28 @@ BEGIN
 	SELECT aw.artist_id INTO aw_artist_id FROM artist_website aw
 	WHERE aw.url = in_url;
 
+	IF aw_artist_id IS NULL THEN
+		RETURN 1;
+	END IF;
+
 	SELECT aw.website_id INTO aw_website_id FROM artist_website aw
 	WHERE aw.url = in_url;
 
+	IF aw_website_id IS NULL THEN
+		RETURN 1;
+	END IF;
+
 	SELECT artist.name INTO artist_name FROM artist
 	WHERE artist.id = aw_artist_id;
 	
 	SELECT website.name INTO website_name FROM website
 	WHERE website.id = aw_website_id;
 	
-	temp_folder_path = concat('Artist/', artist_name, '/', website_name);
+	temp_folder_path = concat('Artists/', artist_name, '/', website_name);
 	
 	UPDATE artist_website SET folder_path = temp_folder_path
 	WHERE url = in_url;
+
+	RETURN 0;
 END;
-$$ LANGUAGE plpgsql;
+$$;