How to simulate a stream of followers in appengine?

Question

I am trying to create tables to build a witness element relationship.

Let's say I have a stream of 140char entries that have a user, hashtag and other text.

Users follow other users, and can also follow hashtags.

I outline how I designed this below, but there are two limitations to my design. I was wondering if others have more reasonable ways to achieve the same goal.

Problems with this:

• The list of subscribers is copied for each entry.
• If a new follower is added or one is deleted, "all" entries must 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?

Answer 1

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Answer 2

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Google App Engine / App Engine. :

http://code.google.com/events/io/2009/sessions/BuildingScalableComplexApps.html

Answer 3

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Answer 4

, Google App Engine, , , :

Tables:
    User    -- a table of users with their attributes
    HashTag -- a table of HashTags with their attributes
    Follows -- a table that defines who follows whom

Columns in the Follows table:
    followed int,         -- the id of the followed entity (could be 
                             User or Hashtag)
    followed_is_user bit, -- whether the followed item is a User
    followed_is_tag bit,  -- whether the followed item is a HashTag
    follower int          -- the id of the follower (this can only be 
                             a User so you may want to make this a foreign 
                             key on the User table)

You could have condensed two columns of bits into one, but this would allow you to add other things that users could do in the future.