☀️ BE TIL Day 12 0329

⬇️ Main Note
https://docs.google.com/document/d/1w-Hvs30xbcNfWlWkO06nhAB1KIvPKHW9b3jCV146HNw/edit

🧀 Single-tone function

➡️ This whole flow is single-tone

🥨 VS Code

// ============ index.js ============
import express from "express";

import { ProductController } from "./mvc/controllers/product.controller.js";
import { CouponController } from "./mvc/controllers/coupon.controller.js";
import { ProductService } from "./mvc/controllers/services/product.service.js";
import { CashService } from "./mvc/controllers/services/cash.service.js";
import { PointService } from "./mvc/controllers/services/point.service.js";

const app = express();
const productService = new ProductService(); // 밖에서 만들어서 안에 넣어주는것
const cashService = new CashService(); // new 한번으로 모든 곳에서 재사용 가능 (싱글톤 패턴)
const pointService = new PointService();

// 상품 API 
const productController = new ProductController(cashService, productService); // Argument (인자 넘기기)
app.post("/products/buy", productController.buyProduct); // 상품 구매하기
app.post("/products/refund", productController.refundProduct); // 상품 환불하기

// 상품권(쿠폰) 구매 API
const couponController = new CouponController(pointService);
app.post("/coupons/buy", couponController.buyCoupon); // 쿠폰(상품권) 구매하기

app.listen(3000, () => {
  console.log(`🚀 Server launched 🚀`);
});

// ============ product.controller.js ============
export class ProductController {
  constructor(cashService, productService) {
    // parameter (변수를 받는 부분 )
    this.cashService = cashService;
    this.productService = productService;
    // cashService라는 거를 cashService 함수로 넣겠다이거
  }

  buyProduct = (req, res) => {
    // 1. 가진 돈 검증
    const hasMoney = this.cashService.checkValue();
    // 2. 판매 여부 검증
    const isSoldout = this.productService.checkSoldout();
    // 3. 상품 구매하는 코드  >> 핵심
    if (hasMoney && !isSoldout) {
      // hasMoney === true && isSoldout === false
      res.send("🛍 상품 구매 완료");
    }
  };

  refundProduct = (req, res) => {
    // 1. 판매 여부 검증
    const isSoldout = this.productService.checkSoldout();

    // 2. 상품 환불하는 코드 >> 핵심
    if (isSoldout) {
      res.send("💳 상품 환불 완료");
    }
  };
}

🥨 Overview Diagram

Service is declared outside, and reuse it inside.

Easy to manage memory, since same function are used multiple times.

No need to declare anything in controllers.

🥨 Flow

➡️ No need to change the whole code. => nest.js handles these actions by IoC.

➡️ Single tone can be used in diverse places since the declaration is held outside: Dependency Injection

🧀 Dependency Injection _ nest.js

ProductController is depending on CashService.
➡️ Here, to change the CashService , ProductController itself should be changed.
➡️ Injecting the dependency from const cashService = new CashService to cashService in index.js which is outside code.
➡️ Injecting the dependency by using nest.js.

nest.js does the job that the developers should do in DI.

Here, the control is taken by nest.js. (制御反転)

This action is called "Inversion of Control"(IoC)
--> Inside nest.js, there is a tool that inverses the control: IoC container.

So what nest.js does, is declaring const cashService = new CashService() .

If config file of nest.js is properly done, IoC is possible.
=> this.cashService : Common commands in nest.js

🥨 Quiz

Q. If DI, then single-tone?
A: No it isn't. Single-tone is just a basic-normal format of nest.js.
=> This can be adjusted by developers.

➡️ Here, yes they are having dependency injection, but they are not in a single-tone format.
➡️ The point of single-tone is once declared, diverse reusages.

🧀 nest.js

Language -- DI-framework
------------------------
  node 	      nest.js
  Java        spring
 Python       Django

➡️ DI-frameworks help dependency injection.

🥨 How to use nest.js

install: yarn add nest.jscreate: npx nest new newProjectNameexecute : node index.js(Executing in postman for example)
POST http://localhost:3000/products/buy
When uplaoding to git hurb, need to delete .git file inside the newly made nest.js file.
➡️ rm -rf .git

🥨 File Structure

🧀 Typescript

🥨 Object type type setting

interface IProfile {
    name: string
    age: number
}

let profile: IProfile = {
    name: 'Joobee',
    age: 18
}

profile.age = "aaa"	// => error

🥨 Typescript Decorator

Structure Flow

function zzz(aaa) {
  console.log("=======");
  console.log(aaa);
  console.log("=======");
}

@zzz
class AppController {}

// ========== public ==========
class Aaa {
  constructor(public myPower) {
    this.myPower = myPower;
  }

  ggg() {
    console.log("안녕 나는 Aaa"); // 의미없는 메소드
  }
}
const aaa = new Aaa(50);
aaa.myPower = 5;

// ========== private ==========
class Bbb {
  constructor(private myPower) {
    // 이 안에서는 myPower 할당 가능함
    this.myPower = myPower;
  }

  ggg() {
    this.myPower = 10; // 접근 가능
    console.log("안녕 나는 Bbb");
  }
}
const bbb = new Bbb(50);
bbb.ggg();
// bbb.myPower = 5; // => 밖에서 접근이 불가능함 // 안에서만 접근 가능함

// ========== Read Only ========== => 안전하게 가져다가 쓰기만 해라 안전하게, 이거임
class Ccc {
  constructor(readonly myPower) {
    // 이 안에서는 myPower 할당 가능함
    this.myPower = myPower;
  }

  ggg() {
    this.myPower = 10; // 접근 불가능 (그냥 가져다가 쓰는거만 가능함)
    console.log("안녕 나는 Bbb");
  }
}
// const ccc = new Ccc(); // 외부에서 사용 불가능