Understanding layers in Clean Architecture: Data Source, Repository, and Usecase layer ᐧ Albert Manuel

Data Source Layer#

Data source is a low-level layer that directly define how our app interact with Database. This layer handles how does our app can get or mutate data on DB.

Example:

import UserModel from "../models/user.model"

export class UserDataSource {
	async findById(id) {
		return await UserModel.findById(id)
	}
}

Repository Layer#

Repository Layer is a layer to abstract the data access. This logic layer doesn’t need to know about DB and it’s implementation. By that, our logic doesnt care whether we use mongodb/mongoose, they only care about the returning result.

Example:

import UserDataSource from "../user/user.datasource"

export class UserRepository {
	constructor(private dataSource: UserDataSource) {}
	
	async getUserId(id){
		return this.dataSource.findById(id)
	}
}

Usecase Layer#

Usecase layer is a layer to implement the business logics or workflows. In terms of clean architecture, we shouldn’t place all business logic in a controller. Instead, we wrapped up all related logic into a usecase layer by it’s context (e.g GetUserUsecase)

The implementation of this layer is to keep controllers clean and neat. The controllers should be focus to handle request and response.

❌ Example of controller without usecase layer

import UserModel from "../models/user.model"

export const getUser = async () => {
	const user = await UserModel.findOne({ email: req.body.email });

	if (!user) return res.status(404).json({ message: "Not found" });
	
	const isMatch = comparePasswords(req.body.password, user.password);
	
	if (!isMatch) return res.status(401).json({ message: "Wrong password" });
	
	const token = generateJwt(user.id);
	
	res.json({ token });
}

✅ Example of controller with usecase layer

import UserRepository from "./user.repository.js"

export class LoginUserUseCase {
  constructor(private userRepo: UserRepository) {}

  async execute(email: string, password: string) {
    const user = await this.userRepo.getByEmail(email);
    if (!user) throw new Error("User not found");

    const match = comparePasswords(password, user.password);
    if (!match) throw new Error("Invalid credentials");

    const token = generateJwt(user.id);

    return { token };
  }
}

import LoginUserUseCase from "./login-user.usecase.js";

const useCase = new LoginUserUseCase(userRepo);

export const getUser = async () => {
	try {
	  const { token } = await useCase.execute(req.body.email, req.body.password);
	  res.json({ token });
	} catch (err) {
	  res.status(401).json({ message: err.message });
	}
}