Django Filter by Foreign Key

Django Filter by Foreign Key

class UserTomonotomo(models.Model):
userid= models.BigIntegerField(null=False, unique=True, db_index=True)
email= models.CharField(max_length=100L, null=True)
######################
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class UserFriends(models.Model):
userid= models.ForeignKey('UserTomonotomo', to_field='userid',
null=False)
friendid = models.BigIntegerField(null=False)
I need to search for UserFriends whose userid > 0,
UserFriends.objects.filter( userid__userid > 0 )
does not work as posted in Django - filtering on foreign key properties !!
What's the fix. I am using django version 1.5.2
Thanks