为什么网页评论内容无法保存到数据库，除了下边代码里的东西，还需要别的吗

<diyclass="comments">
  <p>发表评论</p>
  <p>称: <input type="text" id="tbcommentAuthor" class="authordisabled" size=50 value={requset.user.username}></p>
  <p>评论内容:</p>
  <textarea name="comment_content" id="content" cols=60 rows=10></textarea>
  <button class="btn btn-default commentbtn" onclick="saveComment()">提交评论</button>
</diy>
<script>
  function saveComment() {
    var author = document.getElementById("tbcommentAuthor").value;
    var content = document.getElementById("content").value;

    // 使用AJAX向服务器发送请求，将评论保存到数据库
    var xhr = new XMLHttpRequest();
    xhr.open("POST", "/save_comment", true);
    xhr.setRequestHeader("Content-Type", "application/json");
    xhr.onreadystatechange = function() {
      if (xhr.readyState === XMLHttpRequest.DONE && xhr.status === 200) {
        alert("评论保存成功");
      }
    };
    xhr.send(JSON.stringify({ author: author, content: content }));
  }
</script>

from flask import Flask, request
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = '数据库连接字符串'
db = SQLAlchemy(app)

class Comment(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    author = db.Column(db.String(100))
    content = db.Column(db.Text)

@app.route('/save_comment', methods=['POST'])
def save_comment():
    author = request.json.get('author')
    content = request.json.get('content')

    # 保存评论到数据库
    comment = Comment(author=author, content=content)
    db.session.add(comment)
    db.session.commit()

    return 'OK', 200

if __name__ == '__main__':
    app.run()