有关猫鼬回调函数的问题

Question

我无法使用 post.find 标签运行回调函数。每当我运行 nodemon app.js 时，它都会显示如下错误：

D:\Blog-with-Database-Starting-Files\node_modules\mongoose\lib\model.js:2048
    throw new MongooseError('Model.find() no longer accepts a callback');
    ^

MongooseError: Model.find() no longer accepts a callback       
    at Function.find (D:\Blog-with-Database-Starting-Files\node_modules\mongoose\lib\model.js:2048:11)
    at Object.<anonymous> (D:\Blog-with-Database-Starting-Files\app.js:57:6)
    at Module._compile (node:internal/modules/cjs/loader:1254:14)
    at Module._extensions..js (node:internal/modules/cjs/loader:1308:10)
    at Module.load (node:internal/modules/cjs/loader:1117:32)  
    at Module._load (node:internal/modules/cjs/loader:958:12)  
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:81:12)
    at node:internal/main/run_main_module:23:47

Node.js v18.15.0
[nodemon] app crashed - waiting for file changes before starting...

这是我的 app.js 文件和 ejs 文件：

//jshint esversion:6

const express = require("express");
const bodyParser = require("body-parser");
const ejs = require("ejs");
const _ = require("lodash");
const mongoose = require("mongoose");

const homeStartingContent = "Lacus vel facilisis volutpat est velit egestas dui id ornare. Semper auctor neque vitae tempus quam. Sit amet cursus sit amet dictum sit amet justo. Viverra tellus in hac habitasse. Imperdiet proin fermentum leo vel orci porta. Donec ultrices tincidunt arcu non sodales neque sodales ut. Mattis molestie a iaculis at erat pellentesque adipiscing. Magnis dis parturient montes nascetur ridiculus mus mauris vitae ultricies. Adipiscing elit ut aliquam purus sit amet luctus venenatis lectus. Ultrices vitae auctor eu augue ut lectus arcu bibendum at. Odio euismod lacinia at quis risus sed vulputate odio ut. Cursus mattis molestie a iaculis at erat pellentesque adipiscing.";
const aboutContent = "Hac habitasse platea dictumst vestibulum rhoncus est pellentesque. Dictumst vestibulum rhoncus est pellentesque elit ullamcorper. Non diam phasellus vestibulum lorem sed. Platea dictumst quisque sagittis purus sit. Egestas sed sed risus pretium quam vulputate dignissim suspendisse. Mauris in aliquam sem fringilla. Semper risus in hendrerit gravida rutrum quisque non tellus orci. Amet massa vitae tortor condimentum lacinia quis vel eros. Enim ut tellus elementum sagittis vitae. Mauris ultrices eros in cursus turpis massa tincidunt dui.";
const contactContent = "Scelerisque eleifend donec pretium vulputate sapien. Rhoncus urna neque viverra justo nec ultrices. Arcu dui vivamus arcu felis bibendum. Consectetur adipiscing elit duis tristique. Risus viverra adipiscing at in tellus integer feugiat. Sapien nec sagittis aliquam malesuada bibendum arcu vitae. Consequat interdum varius sit amet mattis. Iaculis nunc sed augue lacus. Interdum posuere lorem ipsum dolor sit amet consectetur adipiscing elit. Pulvinar elementum integer enim neque. Ultrices gravida dictum fusce ut placerat orci nulla. Mauris in aliquam sem fringilla ut morbi tincidunt. Tortor posuere ac ut consequat semper viverra nam libero.";

const app = express();

mongoose.connect("mongodb://127.0.0.1:27017/blogDB", {useNewUrlParser: true})

app.set('view engine', 'ejs');

app.use(bodyParser.urlencoded({extended: true}));
app.use(express.static("public"));


const postSchema = {
  title: String,
  content: String
};

const Post = mongoose.model("Post", postSchema);


app.get("/", function(req, res){
  Post.find({}).then(function(err, foundPosts){
    if(err){
      console.log(err)
    }
    else{
      res.render("home", {
          homeStartingContent: homeStartingContent, 
          posts: foundPosts
      });
    }
  })
});

app.get("/about", function(req, res){
  res.render("about", {aboutContent: aboutContent});
});

app.get("/contact", function(req, res){
  res.render("contact", {contactContent: contactContent});
});

app.get("/compose", function(req, res){
  res.render("compose");
});

Post.find({}, function(err, posts){
  res.render("home", {
    startingContent: homeStartingContent,
    posts: posts
  });
})
app.post("/compose", function(req, res){
  const post = new Post({
    title: req.body.postTitle,
    content: req.body.postBody
  });

  post.save()

  res.redirect("/");

});

app.get("/posts/:postName", function(req, res){
  const requestedTitle = _.lowerCase(req.params.postName);

  posts.forEach(function(post){
    const storedTitle = _.lowerCase(post.title);

    if (storedTitle === requestedTitle) {
      res.render("post", {
        title: post.title,
        content: post.content
      });
    }
  });

});

app.listen(3000, function() {
  console.log("Server started on port 3000");
});

<%- include("partials/header"); -%>
    <h1>Home</h1>
    <p> <%= startingContent %> </p>


  <%  posts.forEach(function(post){ %>

    <h1><%=post.title%></h1>
    <p>
    <%=post.content.substring(0, 100) + " ..."%>
    <a href="/posts/<%=post.title%>">Read More</a>
    </p>


    <% }) %>


<%- include("partials/footer"); -%>

我已将 app.get("/", function(req, res){} 部分中的回调函数格式更改为 Post.find({}).then(function(foundPosts) 但它仍然无法正常工作。请提出任何建议这样做的替代方法，以使回调函数正常运行。

Answer 1

您使用的是什么版本的 Mongoose？在 v6 及更高版本中，他们已停止支持回调函数 以消除混合承诺和回调。例如，这将引发错误。

Post.find({}, function(err, posts){
  res.render("home", {
    startingContent: homeStartingContent,
    posts: posts
  });
})

您需要使用

async/await

或 Promises 代替 - 异步/等待

app.get("/", async function(req, res){
  try {
    const foundPosts = await Post.find({})
    res.render("home", {
            homeStartingContent: homeStartingContent, 
            posts: foundPosts
      });
  } catch (error) {
    console.log(error)
  }})

>>> OR >>>>>
app.get("/", function(req, res){
  Post.find({}).then((foundPosts) => {
      res.render("home", {
          homeStartingContent: homeStartingContent, 
          posts: foundPosts
      })
    .catch(error => {
    console.log(error)
    }
  ))
});

可能漏掉了括号/右括号，但你明白了。

Answer 2

Here is this code, and it works!!!

main().catch(err => console.log(err));

async function main() {
  await mongoose.connect('mongodb://127.0.0.1:27017/blogDB', { useNewUrlParser: true, useUnifiedTopology: true, useUnifiedTopology: true });
};
//Schema 

const postSchema = {
  title: String,
  content: String
};

//Mongoose Model 
const Post = mongoose.model('Post', postSchema);

app.get('/', (req, res) => {
  
  Post.find({})
    .then((posts) => {
      res.render("home", 
      {
        startingContent: homeStartingContent,
        posts: posts
      }) 
      })
      .catch((error) => {
      console.log(error);
      })
});
  
  


app.get('/about', (req, res) => {
  res.render('about', {aboutContent: aboutContent});
});

app.get('/contact', (req, res) => {
  res.render("contact", {contactContent: contactContent});
});

app.get('/compose', (req, res) => {
  res.render("compose");
});

app.post('/compose', (req, res) =>{
  
  //Usage oof mongoose model
  const post = new Post ({
    title: req.body.postTitle,
    content: req.body.postBody
  });

  const saveToPosTDb = 
  async () => {
    await post.save();
    console.log('Compose saved');
  };
  // call the function 
  saveToPosTDb();
  //redirect to
  res.redirect('/');

});

app.get('/posts/:postId', (req, res) => {
  
  //const requestedTitle = _.lowerCase(req.params.postName);

  const requestedPostId = req.params.postId;

  const showPost =
  async () => {
    await Post.findOne({_id:requestedPostId})
    .then (post => {
      
      res.render('post', {
      title:post.title,
      content: post.content
    })
      console.log('Post found');
    })
    .catch (err => {
      console.log(err);
    })
  };

  showPost();

  

});


const PORT = process.env.PORT || 3000;


app.listen(PORT, () => {
  console.log(`Server started on port ${PORT}`);
});