# nodejs - express project structure

# express internals

How express.js works - Understanding the internals of the express library - www.sohamkamani.com/blog - 20180530

# project POV

How to structure a Node.js Express project : Sean McGary 20160327

Embrace the Majestic Monolith - at least to start :

• All of your code is in one place
• Everyone on your team can find things easily
• No npm dependency management hell

Example writing a RESTful API service built on top of PostgreSQL.

Three different layers : Models, lib, and services.

Data model is simple : each "company" can have n many "users" associated.

The directory structure :

.
├── index.js
├── lib
│   ├── company
│   │   └── index.js
│   └── user
│       └── index.js
├── models
│   ├── company.js
│   └── user.js
├── routes
│   └── account
│       └── index.js
└── services
    └── account
        └── index.js

The models schema :

user
----------
- id
- name
- email
- password
- company_id


company
----------
- id
- name


user (1) --> (1) company
company (1) --> (n) user

# model

sequelize (featureful and powerfuly ORM)

Your models can express relationships and are used to build sets of data to eventually send to the end user.

# lib

This is where we start to actually interact with our models.

Create a corresponding file for each model that will wrap basic CRUD operations of a model.

So if we want to list all the users for a company we write a lib/user/index.js file implementing a listUsersForCompany function.

# services

They take different model-level modules and perform some combination of actions.

We want to write a registration system for our application. When a user registers, you take their name, email, and password, but you also need to create a company profile which could potentially have more users down the road.

One company per user, many users per company. Being that a user depends on the existence of a company, we're going to transactionally create the two together to illustrate how a service would work.

So we create a createUser function in lib/user/index.js and a createCompany function in lib/company/index.js.

Then a registerUserAndCompany function wires everything in a services/account/index.js file using sequelize to make it transactional.

# entity POV

Example writing a messenger class in C#.

It is a classic interface implemented by a class :

public interface IMessenger
{
    bool SendMessage();
    void HandleMessage();
    IMessage ComposeMessage();
}

public class Messenger : IMessenger
{
    public bool SendMessage() {}
    public void HandleMessage() {}
    public IMessage ComposeMessage() {}

In JavaScript we use functional style so we split each function in a separated file (no shared state so there is no need to keep them in the same file)

messenger
    __tests__
        composeMessage.test.js
        handleMessage.test.js
        sendMessage.test.js
    composeMessage.js
    handleMessage.js
    sendMessage.js
    index.js // this file combines them all together