resetting default User cache

[ltalirz]

Since the default user of an AiiDA profile is requested a lot, we've introduced a cache for this property:

aiida-core/aiida/orm/users.py

Lines 51 to 70 in cc94a1e

	def get_default(self):
	"""
	Get the current default user
	:return: The default user
	:rtype: :class:`aiida.orm.User`
	"""
	if self._default_user is self.UNDEFINED:
	from aiida.manage.configuration import get_profile
	profile = get_profile()
	email = profile.default_user
	if not email:
	self._default_user = None
	try:
	self._default_user = self.get(email=email)
	except (exceptions.MultipleObjectsError, exceptions.NotExistent):
	self._default_user = None
	return self._default_user

However, short of resetting the manager, there currently doesn't seem to be a way to reset this cache, as one might want to do, for example, after setting a new default user programmatically, deleting the default user, etc.

Resetting this cache could be done at two levels:

1. A specific command for the User.objects collection that resets its _default_user property
2. A generic reset() method for objects - objects are loaded lazily and so you can add a generic method

       @classmethod
       def reset(cls):
           cls._COLLECTIONS = datastructures.LazyStore()

   to aiida.orm.entities.Collection
   This would allow to do User.objects.reset() (same for XXX.objects.reset()).

I'm leaning towards the second option - what do you guys think?

@sphuber
@giovannipizzi

[sphuber]

The second solution you proposed, as implemented, will not only reset the collection of that particular entity and backend, but of all collections that have been instantiated. This is not what we want. I would for now go for a specific reset on the default user on the User collection. Anyway, that is the only collection with real state I think.

[ltalirz]

The second solution you proposed, as implemented, will not only reset the collection of that particular entity and backend, but of all collections that have been instantiated.

Oops - you're right ;-)

Instead of hacking a specific solution for the User, one could probably still do something like this (seems to work)?

    def reset(self):
        """
        Remove lazily constructed collection instance.

        Removes lazily constructed collection instance from LazyStore (constructed again upon next request).
        Useful to clear any internal caches of the collection.
        """
        self._COLLECTIONS.pop((self.entity_type, self.backend))