Extractor for nested Models into their own collections for persistence #78
Description
Some of our models are nested e.g. a 2 winding transformer holds an instance of its node, while in a database or a file only the primary key is referenced in the corresponding field. For simplification and to avoid missing elements when persisting a model, it would be nice to have an extractor class that ensures that all nested models are extracted in their own collection to be passed to the persistence unit.
e.g a collection of Transformer2W can be "extracted" into collections of Transformer2W, OperatorInput and NodeInput