LoopBack4 CoffeeShop

Photo Credits: https://www.pexels.com/photo/six-white-ceramic-mugs-1251175/

Working in progress

CoffeeShop Application Overview

In this CoffeeShop example, there are 3 entities:

• CoffeeShop: the main entity of this example
• Review: review of a particular coffee shop
• Income: income of a particular coffee shop

A coffee shop can have multiple reviews. As illustrated in the diagram below, the CoffeeShop model has a hasMany model relation with the Review model. Besides, the CoffeeShop model has only one Income instance, thus has a hasOne model relation with Income model.

Objectives

In this repo, I'd like to show you how I create this CoffeeShop app step-by-step and add my findings along the way regarding model relations. This CoffeeShop app is inspired by CoffeeShop Review app in LoopBack 3.

Step 1: Create basic models

Create the CoffeeShop, Review and Income models mentioned above.

1. Scaffold a LoopBack4 application using lb4 app command. Tips: If you know you're going to accept all default, you can use the --yes option, i.e. lb4 app your-app-name --yes. It will save you a few keystrokes of accepting the defaults.

2. You can create the models using the lb4 model command. To save you some time, I've created the corresponding json for the 3 models: coffeeshop-model.json

$ lb4 model coffeeshop-model.json --yes
$ lb4 model review-model.json --yes
$ lb4 model income-model.json --yes

Step 2: Create the DataSource and Repositories

Before we can run the relation CLI, we need to have the Repositories created.

Create the datasource and repositories using lb4 datasource and lb4 repository command.

Step 3: Add hasMany relation for CoffeeShop and Review model using CLI

$ lb4 relation
? Please select the relation type hasMany
? Please select source model CoffeeShop
? Please select target model Review
? Foreign key name to define on the target model coffeeShopId
? Source property name for the relation getter reviews
   create src/controllers/coffee-shop-review.controller.ts

Relation HasMany was created in src/

Model Relation Explained

What the command does are:

1. In the CoffeeShop model, it adds the reviews property with the @hasMany decorator
2. In the Review model, it adds the coffeeShopId property.
3. CoffeeShopReviewController is created for CRUD operations on reviews of a specified coffee shop.

If you only need to navigate from CoffeeShop to Review but not the other way round, you can stop here and no need to add the belongsTo relation.

Step 4: Add belongsTo relation for Review and CoffeeShop model using CLI

User flow 1: From models > Database

1. Create the models and model relations

• when lb4 relation is ready, it should be even easier
• modify @model decorator in the Review and Income which are documented in https://github.com/strongloop/loopback-next/pull/2448

2. Use automigrate feature to create the database

• order of database tables are important. Modify database migration script.
• run npm run migrate

3. Modify CoffeeShopRepository to be able to access the ReviewRepository

4. Create CoffeeShopReviewController This is used to do the CRUD operations for reviews related to the coffee shop.

User flow 2: From database > models

Use lb4 discover to discover the models.

Running the app

Run npm start. Go to localhost:3000/explorer.

1. Create some coffee shops - POST /coffee-shops

{
  "name": "My Toronto shop",
  "city": "Toronto"
}

{
  "name": "My NYC shop",
  "city": "New York City"
}

To verify it is working, call GET /coffee-shops

[
  {
    "id": 1,
    "name": "My Toronto shop",
    "city": "Toronto"
  },
  {
    "id": 2,
    "name": "My NYC shop",
    "city": "New York City"
  }
]

2. Create some reviews for particular shops - POST `/coffee-shops/{coffeeshopId}/review

Specify the coffeeShopId as the parameter

For coffeeShopId is 1

{
  "date": "2019-04-26T14:58:15.638Z",
  "rating": 4,
  "comments": "good service"
}

For coffeeShopId is 2

{
  "date": "2019-04-26T14:58:15.638Z",
  "rating": 2,
  "comments": "long lineup all the time"
}

To verify, call GET /coffee-shops/{coffeeShopId}/reviews