如何创建一对多关系表

看了官方文档，但是还是不太明白
想要实现一个简单的评论功能，一条评论对应多条回复

class Comments(db.Model):
    __bind_key__ = 'comments'
    __tablename__ = 'comments'
    id = db.Column(db.Integer,primary_key=True)
    comment_user = db.Column(db.String, nullable=False)
    comment_publish = db.Column(db.DateTime, nullable=False)
    comment_content = db.Column(db.Text,nullable=False)
    reply = db.relationship('Replies',backref='comments',lazy='dynamic')

    def __init__(self, comment_user,comment_content, comment_publish = datetime.datetime.now()):
        self.comment_user = comment_user
        self.comment_content = comment_content
        self.comment_publish = comment_publish

    def __repr__(self):
        return "<Comments %r>" % self.comment_content

class Replies(db.Model):
    __bind_key__ = 'replies'
    __tablename__ = 'replies'
    id = db.Column(db.Integer,primary_key=True)
    reply_user = db.Column(db.String, nullable=False)
    reply_publish = db.Column(db.DateTime, nullable=False)
    reply_content = db.Column(db.Text,nullable=False)
    comments_id = db.Column(db.Integer, db.ForeignKey('comments.id'))

    def __init__(self, reply_user,reply_content, reply_publish = datetime.datetime.now()):
        self.reply_user = reply_user
        self.reply_content = reply_content
        self.reply_publish = reply_publish

    def __repr__(self):
        return "<Replies %r>" % self.reply_content

不知道这样创建的是不是关系表，那插入数据时comments_id又该如何操作

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干嘛要用alchemy