How to resolve UnhandledPromiseRejectionWarning in mongoose?

Question

I\'m trying to fetch data using mongoose.

So everytime i got to fetch the posts from the api -- localhost:3000/api/posts -- i get the foll error that i am unable to

Answer 1

Adding my answer as the others don't give a clear picture.

Since you're making mongoose available as a global promise mongoose.Promise = global.Promise you'll have to handle the promise using .then() and .catch()

Here's how:

...
mongoose.Promise = global.Promise;
mongoose.connect(db)
  .then(res => console.log("Connected to DB"))
  .catch(err => console.log(err))
...

Answer 2

The proper way to handle it is to add a catch clause.

const mongoose = require('mongoose');
mongoose.connect(process.env.MONGODB_URI).catch(function (reason) {
    console.log('Unable to connect to the mongodb instance. Error: ', reason);
});

Answer 3

You need some reject handler for your code, for example:

 router.get('/posts', function(req, res) {
    console.log('Requesting posts');
    post.find({})
        .exec()
        .then(function(posts) {
            res.json(posts);
            console.log(posts);
        })
        .catch(function(error){
            console.log('Error getting the posts');
        });
});

Or don't use promise chaining use just callback function:

router.get('/posts', function(req, res) {
    console.log('Requesting posts');
    post.find({}, function(err, posts){
        if (err) {
            console.log('Error getting the posts');
        } else {
            res.json(posts);
            console.log(posts);
        }
    })
});

Answer 4

workaround => use the event listener

   mongoose.connect('mongodb://localhost:27017/yourDB', {
      useNewUrlParser: true
    });
    mongoose.connection.on('error', err => {
      throw 'failed connect to MongoDB';
    });