I am trying to design tables to buildout a follower relationship.

Say I have a stream of 140char records that have user, hashtag and other text.

Users follow other users, and can also follow hashtags.

I am outlining the way I've designed this below, but there are two limitaions in my design. I was wondering if others had smarter ways to accomplish the same goal.

The issues with this are

1. The list of followers is copied in for each record
2. If a new follower is added or one removed, 'all' the records have to be updated.

The code

class HashtagFollowers(db.Model):
    """
    This table contains the followers for each hashtag
    """
    hashtag = db.StringProperty()
    followers = db.StringListProperty()

class UserFollowers(db.Model):
    """
    This table contains the followers for each user
    """
    username = db.StringProperty()
    followers = db.StringListProperty()

class stream(db.Model):
    """
    This table contains the data stream
    """
    username = db.StringProperty()
    hashtag = db.StringProperty()
    text = db.TextProperty()

    def save(self):
        """
        On each save all the followers for each hashtag and user
        are added into a another table with this record as the parent
        """
        super(stream, self).save()
        hfs = HashtagFollowers.all().filter("hashtag =", self.hashtag).fetch(10)
        for hf in hfs:
            sh = streamHashtags(parent=self, followers=hf.followers)
            sh.save()
        ufs = UserFollowers.all().filter("username =", self.username).fetch(10)
        for uf in ufs:
            uh = streamUsers(parent=self, followers=uf.followers)
            uh.save()



class streamHashtags(db.Model):
    """
    The stream record is the parent of this record
    """
    followers = db.StringListProperty() 

class streamUsers(db.Model):
    """
    The stream record is the parent of this record
    """
    followers = db.StringListProperty()

Now, to get the stream of followed hastags 

    indexes = db.GqlQuery("""SELECT __key__ from streamHashtags where followers = 'myusername'""")
    keys = [k,parent() for k in indexes[offset:numresults]]
    return db.get(keys)

Is there a smarter way to do this?