Mongoose middleware (pre/post hooks) in Express - Mini Project: Build & Apply

Mongoose Middleware with Pre and Post Hooks

📖 Scenario: You are building a simple Express app that uses Mongoose to manage a list of books in a library. You want to add middleware hooks to log messages before saving a book and after deleting a book.

🎯 Goal: Create a Mongoose schema for books, add pre-save and post-delete middleware hooks, and export the model for use in your Express app.

📋 What You'll Learn

Create a Mongoose schema named bookSchema with fields title (string) and author (string).

Create a Mongoose model named Book using bookSchema.

Add a pre-save middleware hook on bookSchema that logs "Saving book: [title]" before saving.

Add a post-delete middleware hook on bookSchema that logs "Deleted book: [title]" after deleting.

💡 Why This Matters

🌍 Real World

Middleware hooks in Mongoose are useful to add logging, validation, or other side effects automatically when data changes in a database.

💼 Career

Understanding Mongoose middleware is important for backend developers working with Node.js and MongoDB to maintain clean and maintainable data logic.

1

Create the Book Schema

Create a Mongoose schema called bookSchema with two string fields: title and author.

Express

const mongoose = require('mongoose');

// Create bookSchema with title and author fields
// Your code here

Need a hint?

Use new mongoose.Schema({ title: String, author: String }) to create the schema.

2

Create the Book Model

Create a Mongoose model called Book using the bookSchema.

Express

const mongoose = require('mongoose');

const bookSchema = new mongoose.Schema({
  title: String,
  author: String
});

// Create Book model from bookSchema
// Your code here

Need a hint?

Use mongoose.model('Book', bookSchema) to create the model.

3

Add Pre-save Middleware Hook

Add a pre-save middleware hook on bookSchema that logs "Saving book: [title]" before saving. Use function(next) and this.title inside the hook.

Express

const mongoose = require('mongoose');

const bookSchema = new mongoose.Schema({
  title: String,
  author: String
});

// Add pre-save hook to bookSchema
// Your code here

const Book = mongoose.model('Book', bookSchema);

Need a hint?

Use bookSchema.pre('save', function(next) { ... }) and call next() after logging.

4

Add Post-delete Middleware Hook

Add a post middleware hook on bookSchema for the 'deleteOne' event that logs "Deleted book: [title]" after deleting. Use function() and access this.title inside the hook.

Express

const mongoose = require('mongoose');

const bookSchema = new mongoose.Schema({
  title: String,
  author: String
});

bookSchema.pre('save', function(next) {
  console.log(`Saving book: ${this.title}`);
  next();
});

// Add post-deleteOne hook to bookSchema
// Your code here

const Book = mongoose.model('Book', bookSchema);

Need a hint?

Use bookSchema.post('deleteOne', { document: true, query: false }, function() { ... }) to access the deleted document.