GAE NDB Revisions: Create automatic versions of your datastore models, allowing you to undo changes!

gae_ndb_revisions

#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""
Create automatic versions of your App Engine Datastore Models, allowing you to undo changes!
 
Usage:
 
    import gae_ndb_revisions
    
    # Add two properties to your Model(s).
    class MyModel(ndb.Model):
      ...
      ndb_rev_number = ndb.IntegerProperty(default=0)  # First rev will be 1, see pre-put.
      ndb_rev_latest = ndb.KeyProperty(kind=gae_ndb_revisions.Revision)
      ndb_rev_previous = ndb.KeyProperty(kind=gae_ndb_revisions.Revision)
    
    # Add the method calls to your Model hooks.
      def _pre_put_hook(self):
        # Tasks to run before saving.
        gae_ndb_revisions.incr_revision(self)

      def _post_put_hook(self, future):
        # Tasks to run after saving.
        gae_ndb_revisions.save_revision(self, future)
"""
 
 
__author__ = 'Eric Higgins'
__copyright__ = 'Copyright 2013, Eric Higgins'
__version__ = '0.0.2'
__email__ = 'erichiggins@gmail.com'
__status__ = 'Development'


import logging

from google.appengine.ext import ndb


__all__ = [
    'incr_revision',
    'save_revision',
    'Revision',
]


def incr_revision(obj):
  """Increment the version number. Intended to be called by pre_put_hook."""
  obj.ndb_rev_number += 1  # Increment revision number.
  obj.ndb_rev_previous = obj.ndb_rev_latest
  _, new_id = Revision.allocate_ids(1)
  obj.ndb_rev_latest = ndb.Key(Revision, new_id)
  logging.debug(u'%s revision is now %d with ID %d', obj.key, obj.ndb_rev_number, new_id)


def save_revision(obj, future):
  """Save a new Revision. Intended to be called by post_put_hook."""
  logging.debug('Asserting a successful put.')
  future.get_result()
  logging.debug(u'Making call to save revision of %s', obj.key)
  Revision.save(obj)


class Revision(ndb.Expando):
  """Stored copy of a revisioned Model, stored copy of latest version."""
  obj_key = ndb.KeyProperty()
  obj_dict = ndb.PickleProperty()
  revision = ndb.IntegerProperty()
  previous_key = ndb.KeyProperty(kind=Revision)
  created = ndb.DateTimeProperty(auto_now_add=True)
  modified = ndb.DateTimeProperty(auto_now=True)

  @classmethod
  def save(cls, obj):
    """Save a copy of the object instance dictionary as a new Revision."""
    logging.info(u'Saving revision %d of %s', obj.ndb_rev_number, obj.key)
    obj_dict = obj.to_dict()
    rev = cls(key=obj.ndb_rev_latest, obj_key=obj_key, revision=obj.ndb_rev_number, previous=obj.ndb_rev_previous, obj_dict=obj_dict)
    # TODO(eric): Use put_async.
    return rev.put()

I think it would be useful to have the user as a standard property of the Revision model.

Also the Kind might be useful.