Add __rand__ and __ror__ to QuerySet [PATCH]

[Sebastian Noack]

It would be nice, if the QuerySet would respect __rand__ and __ror__, when combining it with other QuerySets. Note following example:

class PublicArticleQuerySet(QuerySet):
	def iterator(self):
		for obj in  super(VisibleQuerySet, self).iterator():
			obj._is_public = True
			yield obj
	
	def __or__(self, other):
		self._merge_sanity_check(other)
		# If a PublicArticleQuerySet is or'ed with an other QuerySet
		# we have to clone the other instead of this. So a QuerySet
		# is returned instead of a PublicArticleQuerySet, unless both
		# are PublicArticleQuerySets.
		combined = other._clone()
		combined.query.combine(self.query, sql.OR)
		return combined

	def __and__(self, other):
		self._merge_sanity_check(other)
		# If a PublicArticleQuerySet is and'ed with an other QuerySet
		# we have to clone this instead of the other. So allways a
		# PublicArticleQuerySet is returned.
		combined = self._clone()
		combined.query.combine(other.query, sql.AND)
		return combined

	# We want the behaviour described, also when combining vice versa.
	__ror__ = __or__
	__rand__ = __rand__

class PublicArticleManager(models.Manager):
	def get_query_set(self):
		return PublicArticleQuerySet(self.model).filter(...)

class Article(models.Model):
	...

	objects = models.Manager()
	public_objects = PublicArticleManager()

	def is_public(self):
		if hasattr(self, '_is_public'):
			return self._is_public
		...

I have attached a patch which enables this feature.

[Luke Plant]

Some regression tests, which also show why this useful, need to be added. A simplified example would probably be better, if possible.

There is of course the problem about what happens when you combine two custom QuerySets, both with __ror (or __rand) defined - which one should be used? Perhaps that is telling us something...