Building a REST API using MVC Architecture

In this lesson, we will introduce the Model layer to our server application design. At its core, a server manages data, defines API endpoints for accessing that data using CRUD operation, and provides frontend code to render a nice GUI for the user to more abstractly execute those CRUD operations.

The Model is the portion of the server application that manages the CRUD operations for a server's collection of data. For example, a web-based todo application might:

• store an array of todo objects in memory
• define the endponts GET /API/todos and POST /api/todos to get all todos and to create a new todo
• provide a React application that fetches renders all the todos and a form that lets a user create a new todo.

The piece of code that sits between the endpoints and the array of todo objects is the Model.

Let's jump in!

• Terms
• Model — Adding a Data Management Layer
• Controllers Interact With The Model
• Making API endpoints
  • Route Parameters
  • REST
• Server Organization
• Testing With Postman
• Challenge

Terms

• REST API — an API that conforms to the design principles of the representational state transfer (REST) architectural style.
• Model — an interface for managing a data structure. We will implement a model using a class with static methods for performing CRUD actions on a set of data.
• Postman — a tool for testing HTTP requests
• Route Parameters — named URL segments that are used to capture the values specified at their position in the URL. The captured values are populated in the req.params object

Model — Adding a Data Management Layer

In this lesson, we will build an API that lets users manage a list of fellows. They can:

• (Create) Add a new fellow to the list
• (Read) Get all fellows
• (Read) Get a single fellow
• (Update) Change the name of a fellow
• (Delete) Remove a fellow from the list

To provide a dynamic set of data that allows for full CRUD operations, we need a data layer called a model.

A model is an interface (a set of functions) for managing a data structure. We will implement a model using a class with static methods.

Find the models/Fellow.js file and try the following:

const ben = new Fellow('ben');
const zo = new Fellow('zo');
const carmen = new Fellow('carmen');
const gonzalo = new Fellow('gonzalo');

console.log(Fellow.list())
console.log(Fellow.find(1))
console.log(Fellow.editName(1, 'ZO!!'))
console.log(Fellow.delete(2))
console.log(Fellow.list())

Controllers Interact With The Model

How will this model work within our server?

The flow of control is: Client Request > Express app > Middleware > Controller > Model > Controller > Server Response

In the server applications we've built so far, the data and files we've sent as responses have all been hard-coded.

const serveHello = (req, res, next) => {
  res.send('hello');
}

Now, we can use the Fellow model to get the data we want and send it back to the client:

// Get all the fellows from the `Fellow` class and send them back
const serveFellows = (req, res) => {
  const fellowsList = Fellow.list();
  res.send(fellowsList);
}

// Use a path parameter to find a specific fellow
const serveFellow = (req, res) => {
  const { id } = req.params;
  const fellow = Fellow.find(Number(id));

  if (!fellow) return res.status(404).send(`No fellow with the id ${id}`);
  res.send(fellow);
};

Making API endpoints

We have a class that can manage the list of fellows and we have controllers that can use that model. To let users execute these operations, our server needs API endpoints where a client can send requests.

For example, a GET /api/fellows request will send back all of the fellows managed by the application.

Quiz! (Answer these with a fellow classmate)

• Which action will a GET /api/fellows/5 request perform?
• Which action will a PATCH /api/fellows/5 request perform?
• Which action will a POST /api/fellows request perform?
• Why does the last endpoint not include a number?

Route Parameters

https://expressjs.com/en/guide/routing.html#route-parameters

Named URL segments that are used to capture the values specified at their position in the URL. The captured values are populated in the req.params object

// Route path: /users/:userId/books/:bookId
// Request URL: http://localhost:3000/users/34/books/8989
// req.params: { "userId": "34", "bookId": "8989" }

const serveBook = (req, res) => {
  const { userId, bookId } = req.params;
  console.log(userId, bookId); // 34 8989
}

app.get('/users/:userId/books/:bookId', serveBook)

REST

These API endpoints follow the REST design pattern where endpoints look like: /api/resources/:id.

Representational state transfer (REST) is a design pattern for creating APIs that adhere to 6 pillars:

Uniform interface

• All API requests for the same resource should look the same, no matter where the request comes from.
• The REST API should ensure that the same piece of data, such as the name or email address of a user, belongs to only one uniform resource identifier (URI).
• Resources shouldn’t be too large but should contain every piece of information that the client might need.

Client-server decoupling

• The client and server applications must be completely independent of each other.
• The only information that the client application should know is the URI of the requested resource; it can't interact with the server application in any other ways.
• Similarly, a server application shouldn't modify the client application other than passing it to the requested data via HTTP.

Statelessness

• Each request needs to include all the information necessary for processing it.
• Server applications aren’t allowed to store any data related to a client request.

Layered System

* As a rule of thumb, don’t assume that the client, and server applications connect directly to each other. There may be a number of different intermediaries in the communication loop. * REST APIs need to be designed so that neither the client nor the server can tell whether it communicates with the end application or an intermediary.

Cacheable

• When possible, resources should be cacheable on the client or server side.
• Server responses also need to contain information about whether caching is allowed for the delivered resource.
• The goal is to improve performance on the client side, while increasing scalability on the server side.

Code on Demand (optional)

• REST APIs usually send static resources, but in certain cases, responses can also contain executable code (such as Java applets). In these cases, the code should only run on-demand.

Server Organization

Let's zoom out and look at the organization of the server code now.

server/
├── index.js
├── controllers/
│   └── fellowControllers.js
├── models/
│   └── Fellow.js
└── utils/
    ├── getId.js
    └── fetchData.js

• index.js builds the app, configures middleware, and sets the endpoints. However, the controllers are now imported.
• controllers/fellowControllers.js defines all of the controllers for endpoints relating to fellow data. Each set of data should have its own controllers file.
• models/Fellow.js defines a model for managing fellow data. This model is used exclusively by the fellow controllers. Each set of data managed by the server should have its own model.

By separating our code in this way, we show the separate "layers" of the application.

Testing With Postman

• Download the Postman VS Code Extension
• Create an Account on Postman
• Create a collection called 810 lecture

• Add a request for each of your endpoints:
  • GET /api/fellows
  • GET /api/fellows/:id
  • POST /api/fellows
  • PATCH /api/fellows/:id
  • DELETE /api/fellows/:id
• Requests that require a body, select the body tab, then raw, and choose JSON from the type dropdown.
• Then, test out your server's endpoints using postman

Challenge

Build a Song model and a server application for maintaining a playlist. Each song should have an id, a title, and an artist (at minimum). The model should provide an interface for:

• Creating a new song
• Getting all songs
• Getting a single song
• Updating the title or artist of a song
• Deleting a song

Then, create an endpoint and a controller for each of these pieces of functionality. The endpoints should follow REST conventions and should all begin with /api

Finally, build a frontend react application that can interact with the songs API that you've built. It should be able to:

• Create: Add a new song to the list.
• Read: Display a list of all songs.
• Read: Display a single song.
• Update: Update a single songs's title or artist.
• Delete: Delete a single song.

Here is a recommended React Router page structure for your React app:

• /: The homepage which includes:
  • Form for creating a new song
  • List of all songs
• /songs/:id: The details of a single song which includes
  • The title, artist, and ID of the song
  • A form to submit a new title or artist for the song
  • A button to delete the song from the list