Understanding Mongoose Model.deleteOne() Method with Examples

The Mongoose Model.deleteOne() method is a part of the Mongoose ORM library for MongoDB in Node.js applications. It was added to provide a simple and straightforward way to remove a single document from the collection based on a given condition.

The purpose of Model.deleteOne() is to delete a single document from a MongoDB collection that matches a specified filter. It is designed to ensure that only one document is removed, even if multiple documents match the filter.

Syntax, Parameters, and Return Value

Syntax:

Model.deleteOne(filter, [options], [callback])

Parameters:

• filter: A plain object representing the filter used to select the document to remove.
• options (optional): Additional options such as writeConcern.
• callback (optional): A callback function to execute when the delete operation is complete.

Return Value:

The method returns a promise that resolves with an object containing the deletedCount, which indicates how many documents were deleted.

Code Examples

1. Delete a User by Username

Summary: This example demonstrates how to delete a user with a given username from the ‘users’ collection.

import mongoose from 'mongoose';
const { Schema } = mongoose;

const userSchema = new Schema({ username: String });
const User = mongoose.model('User', userSchema);

async function deleteUserByUsername(username) {
    try {
        const result = await User.deleteOne({ username });
        console.log(result.deletedCount); // Expected output: 1 or 0
    } catch (error) {
        console.error('Error deleting user:', error);
    }
}

deleteUserByUsername('johndoe');

2. Conditional Deletion of a Product

Summary: This example shows how to conditionally delete a product from the ‘products’ collection based on price and stock availability.

import mongoose from 'mongoose';
const { Schema } = mongoose;

const productSchema = new Schema({
    name: String,
    price: Number,
    inStock: Boolean
});
const Product = mongoose.model('Product', productSchema);

async function deleteProductIfPriceIsLowAndOutOfStock(name) {
    try {
        const result = await Product.deleteOne({
            name,
            price: { $lt: 5 },
            inStock: false
        });
        console.log(result.deletedCount); // Outputs the number of documents deleted
    } catch (error) {
        console.error('Error deleting product:', error);
    }
}

deleteProductIfPriceIsLowAndOutOfStock('CheapWidget');

Conclusion

The Model.deleteOne() method is a powerful operation in Mongoose that allows for precise deletion of documents from a collection. Its single-document deletion capability ensures that developers can remove data with precision, while its promise-based interface means it can be cleanly integrated into asynchronous code flows using async or chained with .then() for handling outcomes.