flask 的relationship使用

#一对多  学生是一   (一个学生有多本书)
class Student(db.Model):
    __tablename__ = "student"
    id = db.Column(db.Integer,primary_key=True)
    name = db.Column(db.String(200))
    age = db.Column(db.String(200))
    gender = db.Column(db.String(200))
    #设置relations
    books = db.relationship("Book",backref = "students")

#一对多  书是多   (一个学生有多本书)
class Book(db.Model):
    __tablename__ = "book"
    id = db.Column(db.Integer,primary_key=True)
    book_name = db.Column(db.String(200))
    author = db.Column(db.String(200))
    publish = db.Column(db.String(200))
    price = db.Column(db.String(200))
    types = db.Column(db.String(200))
    pages = db.Column(db.String(200))
    s_id = db.Column(db.Integer,db.ForeignKey(Student.id))

@app.route("/home")
def home():
    #所有的学生
    s_all = Student.query.all()
    return render_template("hh.html",s_all=s_all)

<form action="">
    <table border="1px">
        <a href="{{url_for('insert')}}">新增</a>

        {% for s in s_all%}

<!--        当前学生有哪些书籍   通过relationship-->
            {% for b in s.books %}
                <tr>
                    <td>{{s.name}}</td>
                    <td>{{b.book_name}}</td>
                    <td>{{b.author}}</td>
                    <td>{{b.publish}}</td>
                    <td>{{b.price}}</td>
                    <td>{{b.types}}</td>
                    <td>{{b.pages}}</td>
                    <td>{{s.id}}</td>
                    <td>{{b.s_id}}</td>
                    <td><a href="{{url_for('delete',id = b.id)}}">删除</a></td>
                </tr>
            {% endfor %}
        {% endfor %}

    </table>
</form>