SQLalchemy 更新所有行而不是一行

此代码应该更新数据库中与“post_id”匹配的帖子。但是它将更新表中的每个帖子。

代码已经过编辑，所以它可以正常工作。

@app.route('/update/<post_id>', methods=['GET', 'POST'])
def update(post_id):
  if 'username' not in session:
    return redirect(url_for('login'))
  post = Post.query.get(post_id)  
  form = PostForm(obj=post)

  if request.method == 'POST':
    if form.validate() == False:
      return render_template('update.html', form=form)
    else:
      Post.query.filter(Post.post_id==int(post_id)).update(dict(
        title=form.title.data, body=form.body.data))
      db.session.commit()
      return redirect(url_for('retrieve'))

  elif request.method == 'GET':
    return render_template('update.html', form=form, post_id=post_id)


class Post(db.Model):
  __tablename__ = 'posts'
  post_id = db.Column(db.Integer, primary_key=True)
  author = db.Column(db.String(128))
  title = db.Column(db.String(128))
  body = db.Column(db.Text)

  def __init__(self, author, title, body):
    self.author = author
    self.title = title
    self.body = body

<form method="POST" action="/update/{{post_id}}">