Orchestra : Replace low-level pyMongo by Ming ODM

[davidfischer-ch]

Using MongoDB through a ODM is the best way to enforce database consistency, simplify our code and make it more robust at the cost of a performance overhead.

• http://merciless.sourceforge.net/api/ming.schema.html
• http://merciless.sourceforge.net/odm.html#odm-event-interfaces
• http://blog.mongodb.org/post/27907941873/using-the-python-toolkit-ming-to-accelerate-your
• http://fr.slideshare.net/rick446/rapid-and-scalable-development-with-mongodb-pymongo-and-ming

Ming makes possible some interesting features, such as :

• The schema enforcement layer + The object/document mapper - as it sounds
• MongoDB-in-Memory to allow unit-testing of Orchestra
• Lazy update of schema to allow migration of a database to new schema

This task as is does not add much features to OSCIED, it improve the quality of the code and this is better to make it as soon as possible.

[davidfischer-ch]

I was replacing the low-level pyMongo by Ming and I understand that it is not possible (at least without tweaking Ming) to store 2 foreign id fields pointing to the same kind of Document (here a Media).

Testing TransformJob with doctest
OK
<TransformJob user_id='6582a84b-115f-41e0-b43d-545610a7e9fb'
  media_in_id='8c6ce5a0-37b2-45fc-873b-563211b6c2df'
  profile_id='43960bcd-8933-49c5-9f87-19cb1b889902'
  statistic=I{}
  media_out_id='8c6ce5a0-37b2-45fc-873b-563211b6c2df'
  _id='86ee5908-d1f1-4825-9c43-6d3e25b002a2' revoked=None>
Traceback (most recent call last):
  File "/home/famille/David/git/OSCIED/charms/oscied_lib/TransformJob.py", line 105, in <module>
    pprint(TRANSFORM_JOB_TEST.media_in)
  File "/usr/local/lib/python2.7/dist-packages/ming/odm/property.py", line 209, in __get__
    result = st.extra_state[self] = self.join.load(instance)
  File "/usr/local/lib/python2.7/dist-packages/ming/utils.py", line 18, in __get__
    result = obj.__dict__[self.__name__] = self._func(obj)
  File "/usr/local/lib/python2.7/dist-packages/ming/odm/property.py", line 192, in join
    [ p.name for p in own_props + rel_props ])
ming.odm.property.AmbiguousJoin: Ambiguous join, satisfying keys are ['media_in_id', 'media_out_id']