the iPeng skin has a feature that will always show you whether the currently playing track is in favorites and let you add/remove it with a sincle click toggle button.
This works for both database and url items.
The way it works is, it adds a TT ajax wrapper to the favorites plugin's index.html to return the "favorites" status of the current url:
[code]
IF ajaxRequest;
	FOREACH entry = entries;
		IF (entry.url == url);
			'index|'; entry.index;
		END;
	END;
ELSE;
[/code]

It scans the list of favorites for the requested url and if it finds it, it returns the favorites' id.

Now this is somewhat doable since it's TT and thus runs on the server. I could mimick this through the CLI by frequently querying the favorites list, yet that will cause a bit of traffic.

Would it be possible to add this as a query to the favorites query (or a different one)?

I could live with being able to query url items only, but being able to either use a url or a database id would be even better.

Or is there a simpler way to determine whether a track/url item is already a favorite?