While working on the persistence for the new graph service I encountered a weird behaviour: Each time a persisted graph is altered the edges were removed. So I investigated and it turns out if you are using hibernate inheritance in combination with the @Where clause hibernate only persists the entities which have been modified and removes the relation to the others, but keeps the entities sigh. For more clarity, here is the original code

With the new POC implementation we could solve the current problems of the Topology in OpenNMS. The next step is to take what was learned and implement something similar and more robust in OpenNMS. As this is a big chunk to swallow, the main issue here is on how to split the work into small pieces, as with this kind of API you basically have to almost implement everything before it can be used.

The Topology Map in OpenNMS has some architectural problems. Mainly that there is no "service layer" implemented, which causes mostly performance issues. Besides this no API or persistence model is enforced. This prevents easy integration with 3rd party applications or even provide a new UI implementation. Therefore I started playing around with a new Topology implementation (See issue HZN-1452) for more details). In order to not confuse it with existing implementations, it is called Graph Service or Graph Engine here.