Fixing Mongoose DeprecationWarning: mpromise

Understanding the mpromise Deprecation Warning

When you encounter a deprecation warning related to Mongoose’s built-in promises, it implies that the version of Mongoose you are using relies on an outdated promise library referred to as mpromise. Modern versions of Mongoose, typically starting from version 5.x, have deprecated their built-in promise library in favor of native ES6 promises.

Solutions

Updating Mongoose

The first course of action to resolve this warning is to ensure your project is using a version of Mongoose that supports ES6 promises. Start by updating Mongoose to the latest version using npm:

npm install mongoose@latest --save

Using Native Promises with Mongoose

After updating, it is also recommended to explicitly tell Mongoose to use native JavaScript promises. Place the following line in your application before connecting to the MongoDB database:

const mongoose = require('mongoose');
mongoose.Promise = global.Promise;

Refactoring Code to Use Async/Await

With modern syntax, utilizing async/await along with native promises can streamline your Node.js code. Below is an example that includes database connection and basic model usage:

const mongoose = require('mongoose');
mongoose.Promise = global.Promise;

(async () => {
    try {
        await mongoose.connect('mongodb://localhost:27017/my_database', { useNewUrlParser: true, useUnifiedTopology: true });
        console.log('Database connected successfully.');
    
        const Schema = mongoose.Schema;
        const UserSchema = new Schema({
            name: String,
            age: Number
        });
    
        const User = mongoose.model('User', UserSchema);
    
        let newUser = new User({ name: 'John Doe', age: 30 });
        const savedUser = await newUser.save();
        console.log('User saved:', savedUser);
    } catch (error) {
        console.error('Error connecting to the database:', error);
    }
})();

Conclusion

To address the Mongoose DeprecationWarning: mpromise, updating Mongoose and setting it to use native promises are typically sufficient. However, it is also beneficial to refactor your code to utilize contemporary features like async/await for improved readability and error handling. Following these guidelines not only resolves the deprecation warning but also prepares your codebase for future Mongoose updates and standards.