如何在appengine中建模追随者流？

Question

我正在尝试设计表来建立一个跟随者关系.

假设我有一个包含用户,主题标签和其他文本的140char记录流.

用户关注其他用户,也可以关注主题标签.

我概述了我在下面设计的方式,但我的设计有两个限制.我想知道其他人是否有更聪明的方法来实现同样的目标.

这个问题是

1. 将为每条记录复制关注者列表
2. 如果添加了新的关注者或删除了一个关注者,则必须更新"全部"记录.

代码

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)

有更聪明的方法吗？

Answer 1

您想要解决的问题称为扇出问题.

来自Google App Engine团队的Brett Slatkin为App Engine上的扇出问题提供了一个高效/可扩展的解决方案.你可以在这里找到一个关于这个话题的视频:

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