Need help: Filter for Type A+B , but only current node from B

Hi there,

i have Views up and running, But i can´t make my filter work.

I have two content types: Locations and Parking lots. I want a view that shows all parking lots, but only one location.. The View is shown as a block on the page of the Location.

Right now i can either show all locations and all parking lots, or just the location by using "contextual filter -> nid -> provide default value -> content ID from URL". However i can´t apply this for just one content type.
The PHP filter only returns one value, so i can´t just get all parking NIDs and the current NID with PHP.

(i use this with the gmap plugin if that helps)

Any help is appreciated.