Mongoose中Model.findOne()失效问题求助

Hey there! Let's figure out why your User.findOne() is failing and fix those hidden issues in your code. Here's what's going wrong and how to fix it step by step:

1. Database Connection Conflict #

You're using both MongoClient (native MongoDB driver) and Mongoose to connect to your database. Mongoose has its own built-in connection system, so mixing the two causes conflicts—this is almost certainly why your Mongoose queries like findOne() aren't working.

Fix: Remove the MongoClient code and use Mongoose's native connect() method instead:

mongoose.connect('mongodb://localhost:27017/userDb', { useNewUrlParser: true })
  .then(() => console.log("Mongo DB Connected...!"))
  .catch(err => console.error("Connection error:", err));

2. Mixed Async/Await and Callbacks (Unhandled Errors) #

In your /register route, you're mixing async/await with bcrypt's callback syntax, which creates race conditions and silent failures. You also aren't awaiting user.save() or handling its errors, which can crash your app without feedback.

Fix: Use bcrypt's promise-based methods (with await) instead of callbacks, and properly handle all async operations:

// Inside /register route
const salt = await bcrypt.genSalt(10);
const passwordHash = await bcrypt.hash(req.body.password, salt);

user = new User({
  username: req.body.username,
  password: passwordHash
});

await user.save(); // Await the save operation to ensure it completes
res.send('Registered');

3. Unnecessary hash Field in User Schema #

Bcrypt's generated hash already includes the salt—you don't need to store the salt separately. Your hash field is redundant and can be removed entirely.

Fix: Update your UserSchema:

const UserSchema = new Schema({
  username: { type: String, required: true, minlength: 5, maxlength: 50 },
  password: { type: String, required: true, minlength: 5, maxlength: 1024 }
});

4. Wrong Password Comparison in Login Route #

You're using bcrypt.hash() to compare passwords, which generates a new hash instead of checking if the entered password matches the stored hash. You should use bcrypt.compare() for this task.

Fix: Replace the hash comparison with compare:

// Inside /login route
const isPasswordValid = await bcrypt.compare(req.body.password, user.password);
if (isPasswordValid) {
  res.send('You are logged in!');
} else {
  res.status(400).send('Incorrect password');
}

5. Missing Error Handling for Async Routes #

Your async routes don't have proper try/catch blocks—any uncaught errors will crash your app without logging. Wrap all async code in error handlers to catch issues and send meaningful responses.

Full Fixed Code #

Here's the complete corrected code with all fixes applied:

const express = require('express');
const bcrypt = require('bcryptjs');
const mongoose = require('mongoose');
const app = express();

app.use(express.json());

// Mongoose Database Connection
mongoose.connect('mongodb://localhost:27017/userDb', { useNewUrlParser: true })
  .then(() => console.log("Mongo DB Connected...!"))
  .catch(err => console.error("Connection error:", err));

// User Schema & Model
const Schema = mongoose.Schema;
const UserSchema = new Schema({
  username: { type: String, required: true, minlength: 5, maxlength: 50 },
  password: { type: String, required: true, minlength: 5, maxlength: 1024 }
});
const User = mongoose.model('User', UserSchema);

// Register New User
app.post('/register', async (req, res) => {
  try {
    console.log('try registering : ', req.body);
    
    // Check if user already exists
    let user = await User.findOne({ username: req.body.username });
    if (user) {
      return res.status(400).send('That user already exists!');
    }

    // Encrypt Password
    const salt = await bcrypt.genSalt(10);
    const passwordHash = await bcrypt.hash(req.body.password, salt);

    // Create and save user
    user = new User({
      username: req.body.username,
      password: passwordHash
    });
    await user.save();

    res.send('Registered');
  } catch (err) {
    console.error(err);
    res.status(500).send('Server error occurred during registration');
  }
});

// Login User
app.post('/login', async (req, res) => {
  try {
    console.log('try Login : ', req.body);
    
    // Find user by username
    let user = await User.findOne({ username: req.body.username });
    if (!user) {
      return res.status(400).send('Incorrect username');
    }

    // Validate password
    const isPasswordValid = await bcrypt.compare(req.body.password, user.password);
    if (isPasswordValid) {
      res.send('You are logged in!');
    } else {
      res.status(400).send('Incorrect password');
    }
  } catch (err) {
    console.error(err);
    res.status(500).send('Server error occurred during login');
  }
});

// PORT
const port = process.env.PORT || 3020;
app.listen(port, () => console.log(`listening on port ${port}...`));

Why This Works #

• The database connection is now handled correctly by Mongoose, so queries like findOne() will function as expected.
• Async operations are properly awaited, eliminating race conditions and silent failures.
• Password handling uses bcrypt's intended methods for hashing and comparison.
• All errors are caught and logged, with meaningful responses sent to the client instead of crashing the app silently.

内容的提问来源于stack exchange，提问作者Saloni Sikdar