小细节

@main.route('/<string:id>')
def detail(id):
    m = Topic.find(id=id)
    u = current_user()
    return render_template("topic/detail.html", topic=m, user=u)

@classmethod
def find(cls, id):
    m = cls.one(id=id)
    m.views += 1
    m.save()
    return m

将浏览次数的增加包装成了类方法

def replies(self):
    from .reply import Reply
    ms = Reply.all(topic_id=self.id)
    return ms

在类方法里面，防止交叉引用：
from .reply import Reply