JointJS : How to restrict links per port to one?

API doc for the JointJS library is here: http://www.jointjs.com/api I'm using DEVS plugin for Elements with ports.

I need to restrict number of connections from a port to a single one.

Once a link is made from a port, user shouldn't be able to start a connection from the same port unless the existing connection is removed.

Is it possible without code changes in the library itself?

I was not able to get a hook/entry point to implement this requirement even after looking into API doc and the code itself. Any help or pointers are appreciated.

PS:

• unfortunately I'm not good at Backbone at the moment.
• it was matter of setting magnet="passive" to the port in question, I guess. Just don't know how to do it. (graph is dynamic, not predefined links between elements)

It was as simple as getting element from graph and setting certain attribute on it.

var source = graph.getCell(sourceId);
source.attr('.outPorts circle/magnet', 'passive')