Custom NDB Credentials Model

# For google-api-python-client
from google.appengine.api import users
from google.appengine.ext import ndb

from oauth2client import appengine


class CurrentUserEmailProperty(ndb.StringProperty):
  def _set_value(self, entity, value):
    if value is None:
      current_user = users.get_current_user()
      if current_user is not None:
        value = current_user.email()
    super(CurrentUserEmailProperty, self)._set_value(entity, value)

  def _fix_up(self, cls, code_name):
    """Internal helper called to register the property with the model class.

    Overrides the _set_attributes method on the model class to interject this
    attribute in to the keywords passed to it. Since the method _set_attributes
    is called by the model class constructor to set values, this -- in congress
    with the custom defined _set_value -- will make sure this property always
    gets set when an instance is created, even if not passed in.
    """
    original_set_attributes = cls._set_attributes

    def CustomSetAttributes(setattr_self, kwds):
      if self._code_name not in kwds:
        kwds[self._code_name] = None
      original_set_attributes(setattr_self, kwds)

    cls._set_attributes = CustomSetAttributes
    super(CurrentUserEmailProperty, self)._fix_up(cls, code_name)


class CustomCredentialsModel(appengine.CredentialsNDBModel):
  user_email = CurrentUserEmailProperty(required=True, indexed=False)



appengine.CredentialsModel = CustomCredentialsModel