Comment 16 for bug 1158684

Ivar's patch in comment 15 works around this Nova bug by changing the schema to set the port_id foreign key to null on delete. I think this is sufficient for the Juno GBP release.

Alternatively, it should be possible to add an ML2 mechanism driver that "intercepts" port delete and deletes the corresponding GBP policy target. Ivar's work-around is preferable for at least two reasons: 1) It is independent of the core plugin whereas this would only work with ML2, and 2) Nova should not be deleting the port (and/or policy target) when it was created externally to Nova.

Once the Nova bug is fixed, we should change schema so the port_id foreign key is no longer be set to null on delete.