Clean architecture example API server (typescript + express)

About

This is a simple API server as an example of the clean architecture.

The API server can create, read, update, and delete users. Here, a user has two attributes: id and name. It is assumed that name must not be empty and it must be unique among all users.

In addition to simple CRUD functions, this API server implements API request validations. It is designed that each validation is conducted in an appropriate architectural layer.

The following tech stack is used in the implementation.

language: Typescript
framework: Express (only for routing and parse of requests)
DB: in-memory mock DB

If you find any bugs, or design & architecture problems, please notify me by creating an issue!

How to use

Prerequisites

Node.js v14.x
yarn

Start server

Type yarn install and yarn start at the root directory. The server starts at localhost:8000.

Available endpoints

Available endpoints and example requests are the following. (Note that an initial user exists with name "initial-user" even before creating a user).

Create user

curl -X POST localhost:8000/users -H 'Content-Type:application/json' -d '{"name": "hoge"}'

List all users

curl -X GET localhost:8000/users

Find user by ID (replace with an appropriate value)

curl -X GET localhost:8000/users/<USER ID>

Update user

curl -X PUT localhost:8000/users/<USER ID> -H 'Content-Type:application/json' -d '{"name": "fuga"}'

Delete user

curl -X DELETE localhost:8000/users/<USER ID>

tests

Type yarn test at the root directory to run tests.

Design notes

Validation in each architectural layer

As suggested in this blog, each validation logic should be implemented in an appropriate layer in the Clean Architecture according to its characteristics.

In this API server, the validation types and the corresponding architectural layers can be summarized as follows.

API endpoint	Interface Adapters (Controller)	Application Business Rules (Use Case Interactor)	Enterprise Business Rules (Entity)
POST /users	types and structure of request parameters		if `name` is not empty, if `name` is unique among all users
GET /users	types and structure of request parameters
GET /users/{id}	types and structure of request parameters	if user with requested `id` exists
PUT /users/{id}	types and structure of request parameters	if user with requested `id` exists	if `name` is not empty, if `name` is unique among all users
DELETE /users/{id}	types and structure of request parameters	if user with requested `id` exists

Components

The following figure shows the components and classes in this system.

The dependencies among the components are designed to obey the "dependency rule" of the clean architecture.

Note that the UserValidator interface and UserValidatorImpl class are responsible for the validation of the user entity in the enterprise business rules layer.

nakaakist/clean-architecture-example-typescript

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