ExpressX

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Getting started ​

Create a project ​

Let's create a new folder for our application:

bash
mkdir expressx-project
cd expressx-project

Since any ExpressX application is a Node application, we can create a default package.json using npm:

bash
npm init es6 --yes

The es6 argument adds "type": "module" in package.json. Beware! All further module imports must made with es6/esm import syntax.

Install ExpressX ​

bash
npm install @jcbuisson/express-x

Our first server application ​

Now we can create an ExpressX application which will provide a complete CRUD API on a User resource backed in a Prisma database

js
// app.js
import { expressX } from '@jcbuisson/express-x'
import { PrismaClient } from '@prisma/client'

const prisma = new PrismaClient()

// `app` is a regular express application, enhanced with express-x services and real-time features
const app = expressX()

// create two CRUD database services with the Prisma methods: `create`, 'findUnique', etc.
app.createService('user', {
   findUnique: prisma.User.findUnique,
   create: prisma.User.create,
   update: prisma.User.update,
   delete: prisma.User.delete,
})
app.createService('post', {
   findUnique: prisma.Post.findUnique,
   create: prisma.Post.create,
   update: prisma.Post.update,
   delete: prisma.Post.delete,
})

app.httpServer.listen(8000, () => console.log(`App listening at http://localhost:8000`))

Before running it we need to setup the corresponding database.

Create the database ​

Prisma is used in this example to talk to a relational database.

First, provide the database schema in prisma/schema.prisma:

prisma
generator client {
   provider = "prisma-client-js"
}

model User {
   id          Int       @default(autoincrement()) @id
   name        String
   posts       Post[]
}

model Post {
   id          Int       @default(autoincrement()) @id
   text        String
   author      User      @relation(fields: [authorId], references: [id], onDelete: Cascade)
   authorId    Int
}

datasource db {
   provider = "sqlite"
   url      = "file:./dev.db"
}

Then create the database:

bash
npx prisma db push

In this example which uses SQLite, the database file is created at prisma/dev.db. Of course you can other RDBMS such as PostGres, MySQL, MongoDB, etc.

Run the server ​

bash
node app.js

It prints the following lines in the console:

bash
App listening at http://localhost:8000

Create the client ​

We first need to install the client library:

bash
npm install @jcbuisson/express-x-client socket.io-client

Create the following client NodeJS script:

js
// client.js
import io from 'socket.io-client'
import expressXClient from '@jcbuisson/express-x-client'

const socket = io('http://localhost:8000')

const app = expressXClient(socket)

async function main() {
   const user = await app.service('user').create({
      data: {
         name: "Joe"
      }
   })
   await app.service('post').create({
      data: {
         authorId: user.id,
         text: "Post#1"
      }
   })
   await app.service('post').create({
      data: {
         authorId: user.id,
         text: "Post#2"
      }
   })
   const joe = await app.service('user').findUnique({
      where: {
         id: user.id,
      },
      include: {
         posts: true,
      },
   })
   console.log('joe', joe)
   process.exit(0)
}
main()

For simplicity we use a node client, but you would write something similar with your favorite front-end framework.

You can use the exact same statements on services on the client side as you would on the server side, such as: app.service('user').create(...). Of course the app object on the client is quite different that the app object on the server; you can find explanations here.

Now run the client script:

bash
node client.js

It prints the following lines in the console:

json
joe {
  id: 11,
  name: 'Joe',
  posts: [
    { id: 12, text: 'Post#1', authorId: 11 },
    { id: 13, text: 'Post#2', authorId: 11 }
  ]
}

We have a GraphQL-like experience with the nested posts, thanks to Prisma and its use through ExpressX services. We can harness the full power of Prisma from the client-side, without being constrained as we would with a simple REST API.

Real-time applications ​

When a connected client calls a service method, two things happen on method completion:

  • the resulting value is sent to the client
  • an event is emitted, and sent to connected clients we'll call subscribers. The calling client may or not be one of those subscribers.

For example in a medical application, whenever a patients's record is modified, an event could be sent to all his/her caregivers.

Channels are used for this pub/sub mechanism. Service methods publish events on channels, and clients subscribe to channels in order to receive those events. ExpressX provides functions to configure which events are published to which channels. A channel is represented by a name and you can create and use as many channels as you need.

In the following example, every time a client connects to the server, it joins (= is subscribed to) the 'anonymous' channel. And whenever an event is emited by the post or user service, this event is published on this channel, and then broacasted to all connected clients, leading to real-time updates.

js
// app.js
import { expressX } from '@jcbuisson/express-x'
import { PrismaClient } from '@prisma/client'

const prisma = new PrismaClient()

// `app` is a regular express application, enhanced with express-x services and real-time features
const app = expressX(prisma)

// create two CRUD database services with the Prisma methods: `create`, 'update', etc
app.createService('user', {
   findUnique: prisma.User.findUnique,
   create: prisma.User.create,
   update: prisma.User.update,
   delete: prisma.User.delete,
})
app.createService('post', {
   findUnique: prisma.Post.findUnique,
   create: prisma.Post.create,
   update: prisma.Post.update,
   delete: prisma.Post.delete,
})

// publish
app.service('user').publish(async (post, context) => {
   return ['anonymous']
})
app.service('post').publish(async (post, context) => {
   return ['anonymous']
})

// subscribe
app.addConnectListener((socket) => {
   app.joinChannel('anonymous', socket)
})

app.httpServer.listen(8000, () => console.log(`App listening at http://localhost:8000`))

Here is how a client may listen to channel events:

js
import io from 'socket.io-client'
import expressXClient from '@jcbuisson/express-x-client'

const socket = io('http://localhost:8000', { transports: ["websocket"] })

const app = expressXClient(socket)


app.service('user').on('create', (user) => {
   console.log('User created', user)
})

app.service('post').on('create', (post) => {
   console.log('Post created', post)
})


async function main() {
   const user = await app.service('user').create({
      data: {
         name: "Joe"
      }
   })
   await app.service('post').create({
      data: {
         authorId: user.id,
         text: "Post#1"
      }
   })
   await app.service('post').create({
      data: {
         authorId: user.id,
         text: "Post#2"
      }
   })
   const joe = await app.service('user').findUnique({
      where: {
         id: user.id,
      },
      include: {
         posts: true,
      },
   })
   console.log('joe', joe)
   process.exit(0)
}
main()

The listener is triggered whenever the client receives from the server a create event from the service post. This event occurs on the completion of a call app.service('post').create() on the server.