Express MongoDB

  • cookie-parser: Used to parse the cookie header and populate req.cookies (essentially provides a convenient method for accessing cookie information)
  • debug: A tiny node debugging utility modeled after node core’s debugging technique
  • morgan: A HTTP request logger middleware for node
  • http-errors: Create HTTP errors where needed ( for express error handling)
"scripts": {
"start": "node ./bin/www",
"devstart": "nodemon ./bin/www",
"serverstart": "DEBUG=express-locallibrary-tutorial:* npm run devstart"

Using a Database (with Mongoose)

This section explains how object schema and models are declared, the main field types, and basic validation. It also briefly shows a few of the main ways in which you can access model data.

  • Using the database native query language (e.g SQL)
  • Using an Object Data Model(“ODM”) or an Object Relational Model (“ORM”)
    An ODM/ORM represents the website’s data as JavaScript objects, which are then mapped to the underlying database. Some ORMs are tied to a specific database, while others provide a database-agnostic backend.

Designing the models

We are going to design a model for the library. We need to store information about books (title, summary, author, genre, ISBN) and we might have multiple copies available (with globally unique ids, availability statuses, etc). We might need to store more information about the author than just their name. We want to be able to sort information based on the book title, author, genre, and category.

brew tap mongodb/brew
brew install mongodb-community@5.0
brew services start mongodb/brew/mongodb-community
mongod --config /usr/local/etc/mongod.conf

Defining and creating models

Models are defined using the schema interface. The Schema allows you to define the fields stored in each document along with their validation requirements and the default values.

Defining schemas and creating a model

The code below shows how you might define a simple schema.

const mongoose = require('mongoose');
const Schema = mongoose.Schema
const SomeModelSchema = new Schema({
name: String,
binary: Buffer,
living: Boolean,
updated: { type: Date, default: },
age: { type: Number, min: 18, max: 65, required: true},
mixed: Schema.Types.Mixed,
_id: Schema.Types.ObjectId
});const SomeModel = mongoose.model('SomeModel', SomeModelSchema)


Mongoose provides built-in and custom validatiors, and synchronous and asynchronous validators. It allows you to specify both the acceptable range of values and the error message for validation failure in all cases.

  • All SchemaTypes have the built-in required validator
  • Numbers have min and max validators
  • Strings have: enum, match, maxLength, and minLength

Virtual properties

Virtual properties are document properties that you can get and set but that does not get persisted to MongoDB. The getters are useful for formatting or combining fields, while setters are useful for de-composing a single value into multiple values for storage.

Methods and query helpers

A schema can also have instance methods, static methods, and query helpers. The instance and static methods are similar, but with the obvious difference that an instance method is associated with a particular record and has access to the current object. Query helpers allow you to extend mongoose’s chainable query builder API.

Using models

Once you have created a schema you can use it to create models. The model represents a collection in the database that you can search, while the mode’s instances represent individual documents that you can save and retrieve.

Connect to MongoDB

const mongoose = require('mongoose');const mongoDB = 'mongodb://';mongoose.connect(mongoDB, { useNewUrlParser: true, useUnifiesTopology: true });const db = mongoose.connection;db.on('error', console.error.bind(console, 'connection error'));

Define the Library Schema

We will define a separate module for each model. and start by creating a folder for our models and then create separate files for each of the models.




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