hello-world.md

Getting started

The goal of this section is to describe the Pipeline.StepFunctions required to have bautajs-express up and running in a sort of hello world example.

Prerequisites

• An empty project
• Project already initialized (it has a package.json). npm init
• A npm start script on the package.json with the command node server.js

Step 1 Install bauta

  npm install @bautajs/express @bautajs/core

Step 2 Create a server file that uses bautajs/express

const express = require('express');
const { BautaJSExpress } = require('@axa/bautajs-express');
const apiDefinition = {};
const apiOptions = {
  apiDefinition
};
(async () => {
 const bautJSExpress = new BautaJSExpress(apiOptions);
 const app = express();
 const router = await bautaJS.buildRouter();

 app.use('/v1', router);
 app.listen(3000, err => {
    if (err) throw err;
    bautaJS.logger.info('Server listening on localhost: 3000');
  });
})();

At this point, if you try to start the server, it will not work because api definitions are empty.

Step 3 Configure api-definitions

The information about api definitions is Here.

Let's assume that we have the minimal empty with zero functionality api definitions (do not worry, it will grow to some usefulness later on). It could be in a separate file api-definitions.json with the following content:

  {
    "openapi": "3.0.0",
    "info": {
      "version": "v1",
      "title": "Example API"
    },
    "servers": [
      {
        "url": "/api/v1/"
      }
    ],
    "paths": {
      "/greetings": {
        "get": {
          "summary": "be a polite greeting service",
          "operationId": "getGreetings",
          "responses": {
            "200": {
              "description": "polite greeting ok",
              "content": {
                "application/json": {
                  "schema": {}
                }
              }
            }
          }
        }
      }
    }
  }

There is a lot of information here, but let's focus only on two fields:

• first element inside paths element: In this case it has the value /greetings. This is the subdomain of the service that we are exposing.
• operationId: This element has the value getGreetings. It is a pointer to the right method that will implement the logic of our greeting operation.

Now let's modify slightly the server.js file:

const express = require('express');
const { BautaJSExpress } = require('@axa/bautajs-express');
const apiDefinition = require('./api-definition');
const apiOptions = {
  apiDefinition
};
(async () => {
 const bautJSExpress = new BautaJSExpress(apiOptions);
 const app = express();
 const router = await bautaJS.buildRouter();

 app.use(router);
 app.listen(3000, err => {
    if (err) throw err;
    bautaJS.logger.info('Server listening on localhost: 3000');
  });
})();

Finally, let's try again running the server with npm run start, and now it should work.

Now, only the endpoint '/greetings' will be exposed but because we don't have any implementation by default we will receive a not found error (HTTP Status code 404).

Step 4 hello world implementation

Finally, we have to create or first resolver. Let's call this file resolver.js. So, let's do the following commands in the root of the project:

mkdir server
cd server
mkdir resolvers
cd resolvers
mkdir hello-world
cd hello-world
touch resolver.js

Its content should be as follows:

const { resolver } = require('@axa/bautajs-core');
module.exports = resolver(operations =>
    operations.getGreetings.setup(() => ({
        message: 'hello world'
      })
  );

First of all, resolver decorator is only used in edition time, to allow the editor to show the signature of the different methods and parameters. At this point it has no other usage in runtime and can be ignored for our explanations.

operations is the reference of all the operations for the middleware. From them, we have at the pointer .getGreetings the version defined in the api definition and the id of the operation that must match the operationId in the api definition. Finally, the setup method requires a pipeline parameter p, in which we push Pipeline.StepFunctions. Our pipeline is very simple and has only one Pipeline.StepFunction, that returns the message we desire. If we have start the server and we call the method GET /api/v1/greetings now, as expected, we are greeted!