Disallow links from ToNode


I have two kinds of nodes: apartment nodes and room nodes. The user is allowed to link a single room node to an apartment node. In order to restrict further links from the room node I’ve overridden IsValidFrom and IsValidTo in the linking tool. The apartment node is not allowed as a from node of a link.
Now, what I want to have is the user to drag from the room node over to the apartment node to create a link between the two. And I want it only this way. The framework however still allows me to start my link at the apartment node over to the room node and create a link this way as well because it also allows the user to start a link with the ToNode. When I set IsValidTo to always return false, I cannot drag the link from the room to the apartment anymore even though IsValidLink returns true.
How can I restrict this? Is there a way to check from which node the link operation has actually started in the IsValidTo function?

Would setting LinkingTool.Direction = “ForwardsOnly” suffice?

That worked, thank you