Backend and search engine for Nefertari

Some issues to get basic engine working

• finish implementing relationship fields.

  • implement ondelete and onupdate?

  • improve efficiency of saving and loading of related objects. maybe lazy or bulk loading of related objects. Maybe check related objects to see if they are dirty before saving them.

  • there is an issue where obj _ids are not available until the objects are saved. so when saving related objects you can't put the backref id in place until after the referring object is saved. thus the first time you save an object with backrefs to it, the backrefs won't be saved.

• tests - we need test relationship fields.

Later move all es search from other engines and nefertari to this package:

• Move existing es integration out of nefertari (and other engines) into es engine

• need a way to generate an es model or mapping given an sql or mongo model. this shouldn't be too hard, since the field names are mostly the same.

• try to re-use existing part of the es engine. for example, probably can re-use exiting base classes and fields in order to recreate something like the existing get_es_mapping.

• need a way to delegate search to es (or other secondary engine?). maybe just call get_collection on the generated es model.

• will still need hooks in sql and mongo engines to update es models when models are changed. it might make sense to change these hooks to generate pyramid events. then the es engine can listen for these events, thus de-coupling the engines.