sqlchemy 多对多关系如何插入一条数据

tags = db.Table('tags',
            db.Column('tag_id', db.Integer, db.ForeignKey('tag.id')),
            db.Column('page_id', db.Integer, db.ForeignKey('page.id')),
            db.Column('name', db.VARCHAR(64), nullable=False)
)

class Page(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    num = db.Column(db.Integer)
    tags = db.relationship('Tag', secondary=tags, backref=db.backref('pages', lazy='dynamic'))

    def __init__(self, num):
        self.num = num

class Tag(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.VARCHAR(32))

    def __init__(self, name):
        self.name = name

if __name__ == '__main__':
    db.create_all()
    tag = Tag('test')
    db.session.add(tag)
    db.session.commit()

    page = Page(3843)
    db.session.add(page)
    db.session.commit()

    page.tags.append(tag)
    db.session.add(page)
    db.session.commit()

报错如下： (_mysql_exceptions.OperationalError) (1364, "Field 'name' doesn't have a default value")

问题来了，怎么插入 name 的值了？？？？？

Column

integer

page