我是mongodb和nodejs的新手，我保存了一篇文章，文章中有文字和图片到mongodb数据库，我试图获取信息，但图片似乎未定义。
这是后模型

const mongoose = require("mongoose");
const { Schema, model } = mongoose;
const postSchema = new Schema(
  {
    title: String,
    summary: String,
    content: String,
    file: String,
  },
  {
    timestamps: true,
  }
);

const PostModel = model("Post", postSchema);

module.exports = PostModel;

在服务器端，我使用multer中间件传递图像

const multer = require("multer");
const blogStorage = multer.diskStorage({
  destination: (req, file, callback) => {
    callback(null, "./api/postblog");
  },
  filename: (req, file, callback) => {
    callback(null, `${Date.now()}_${file.originalname}`);
  },
});

const postblog = multer({ storage: blogStorage });

app.post("/post", postblog.single("file"), async (req, res) => {
  const { title, summary, content } = req.body;
  const { originalname, path } = req.file;
  const newPath = path;
  const postDoc = await Post.create({
    title,
    summary,
    content,
    file: newPath,
  });
  res.json(postDoc);
});

app.get("/post/:id", async (req, res) => {
  const { id } = req.params;
  const postDoc = await Post.findById(id);
  res.json(postDoc);
});

这是postPage.js页面，我在这里通过id获取帖子

const PostPage = () => {

   const [postInfo, setPostInfo] = useState(null);
   const { userInfo } = useContext(UserContext);
   const { id } = useParams();
   useEffect(() => {
     fetch(`http://localhost:4000/post/${id}`).then((response) => {
       response.json().then((postInfo) => {
         setPostInfo(postInfo);
       });
     });
   }, []);

   if (!postInfo) return "";

  return (
    <div className="post-page">
      <h1>{postInfo.title}</h1>
      <time>{formatISO9075(new Date(postInfo.createdAt))}</time>
      <div className="image">
        <img src={`http://localhost:4000/${postInfo.cover}`} alt="" />
      </div>
      <div
        className="content"
        dangerouslySetInnerHTML={{ __html: postInfo.content }}
      />
    </div>
  );
}

export default PostPage

我得到了除图像之外的所有文件，控制台显示：（未找到）返回首页（未找到）
这是我的博客：
Post collection
这是我的项目结构：project structure
我试了这行代码：应用程序使用（“/postblog”，表达静态（__目录名+“/postblog”））;