In this series, we will work through creating a basic LoopBack 4 application that exposes REST APIs, calls out to GitHub APIs through octokat.js (a GitHub API client) to get the number of stargazers on a user-specified GitHub organization and repository, and persists the data into a Cloudant database.

Previously in Part 2

In the Part 2 of this series, we created a REST endpoint that gets the number of stargazers for a GitHub repository by using octokat.js.

Since GitHub does not keep track of the history on how the number of stargazers change over time, we’re building that functionality ourselves. In this article, we are going to complete the application by persisting such data together with the timestamp into a Cloudant database.

Creating Model, DataSource and Repository

Step 1: Defining the Model

First, we define the model for the data to be persisted in the database. The model GHStars we are creating extends from a base class Entity from @loopback/repository and has the following properties:

  • org: GitHub organization
  • repo: GitHub repository
  • stars: number of stars for the given org/repo
  • countdate: date of the entry being created

Under models folder, create a file called gh-stars.model.ts. Add the snippet below to gh-stars.model.ts.

export class GHStars extends Entity {
     * making the id as generated
        id: true,
    id?: number;

        required: true,
    org: string;

        required: true,
    repo: string;

        required: true,
    stars: number;

        required: false,
        type: 'string',
        format: 'date'
    countdate: Date;

Step 2: Configuring the Datasource

We’re going to declare the datasource connection to the Cloudant database through datasources.json. In this article, Cloudant service on IBM Cloud is used. Feel free to use another database from the supported database connectors. Since LoopBack 4 is leveraging the juggler in LoopBack 3 through the legacy juggler bridge, defining the datasource is similar to what we do in LoopBack 3 for those who are familiar with the older versions of LoopBack. For details, see

Step 2a: Creating datasources.json for the Database Connection

Create a folder config at the root of the project and a file within this folder called datasources.json, with the following content. Replace the url with your Cloudant instance.

    "name": "db",
    "connector": "cloudant",
    "url": "",
    "database": "ghstars"

Important: If you’re pushing your application to GitHub, make sure you are not committing this file as well. To do this, add config/ in the .gitignore file.

Step 2b: Creating DataSource Class

Next, create a DataSource class which reads the datasources.json we just created.

Create db.datasource.ts in datasources folder.

import * as path from 'path';

import {juggler, DataSourceConstructor} from '@loopback/repository';

const dsConfigPath = path.resolve('config', 'datasources.json');
const config = require(dsConfigPath);
export const db = new DataSourceConstructor(config);

Step 3: Creating Repository

A Repository is a type of Service that represents a collection of data within a DataSource. In this step, we are going to bind the model with the datasource.

Create ghstar.repository.ts in repositories folder, with the following snippet:

import {DefaultCrudRepository, DataSourceType} from "@loopback/repository";
import {GHStars} from "../models/gh-stars.model";
import {inject} from '@loopback/core';

export class GHStarRepository extends DefaultCrudRepository<GHStars, typeof> 
    constructor(@inject('datasources.db') protected datasource: DataSourceType) {
        super(GHStars, datasource);

Step 4: Using Repository Mixin in the Application

We are going to use the Repository Mixin to bind the Application and Repository in application.ts.

Step 4a: Change the application to be extended from BootMixin(RepositoryMixin(RestApplication))


export class GitHubApplication extends BootMixin(RepositoryMixin(RestApplication)) {

Add the following import statements:

import {RepositoryMixin, Class, Repository, juggler} from '@loopback/repository';
import {db} from './datasources/db.datasource';

Note: The unused imports are necessary as type information from these imports are needed when RepositoryMixin is used.

Step 4b: Binding the Datasource

This can be done by setting up bindDataSource() function and calling it in the constructor of GitHubApplication.

bindDataSource() {

Step 5: Putting Things Together

As the final step, we are going to create a POST endpoint /repo/{org}/{repo}/stars in the GHRepoController that:

  • gets the number of stargazers for a given GitHub repo
  • stores the information to Cloudant database

Step 5a: Update the Contructor for the GHRepoController

In controllers/gh-repo.controller.ts, update the constructor to inject repositories.GHStarRepository.

Add the following import statement:

import {db} from './datasources/db.datasource';
    @repository(GHStars, db)
    public ghstarRepository : GHStarRepository,) {}

Step 5b: Add New Function for the POST Endpoint

In the same GHRepoController, add a new function:

   * Get the GitHub star count
   * and persist the value in a database
  async storeRepoStargazers(
    @param.path.string('org') org: string,
    @param.path.string('repo') repo: string
  ): Promise<GHStars> {
    debug('org/repo', org, repo);
    //gets the number of stargazers for a given GitHub repo
    const repoContent = await octo.repos(org, repo).fetch();
    const stargazerNum = repoContent.stargazersCount;
    //stores the information to database
    const ghStar = new GHStars(); = org;
    ghStar.repo = repo;
    ghStar.countdate = new DateType().defaultValue();
    ghStar.stars = stargazerNum;
    return await this.ghstarRepository.create(ghStar); 

Running End-to-End

Restart the application. Go to the API explorer localhost:3000/swagger-ui, select GHRepoController > POST /repo/{org}/{repo}/stars. Type in the org and repo that you’d like to know about the number of stargazers.

After running it, you should see an entry in the Cloudant database look like:

  "_id": "f0a792a6dd9dc2c60186e9e2d91441b7",
  "_rev": "1-2f128fd392901a6390c8cf3c0590f458",
  "org": "strongloop",
  "repo": "loopback-next",
  "stars": 529,
  "countdate": "Tue Mar 20 2018 13:42:48 GMT-0400 (EDT)",
  "loopback__model__name": "GHStars"


In this blog series, we built this LoopBack GitHub application using LoopBack 4 step-by-step:

Code Repository

The code repository can be found here.

git clone

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