介紹

函數(shù)式編程（FP）因其可組合性、可測試性和魯棒性而廣受歡迎。在 JavaScript 生態(tài)系統(tǒng)中，像 fp-ts 這樣的庫為 TypeScript 帶來了強(qiáng)大的 FP 概念，讓您可以編寫更干凈、更可靠的代碼。

本文探討 fp-ts 概念，例如 Option、Either、Task、Reader 和 ReaderTaskEither。我們將使用 fp-ts、pg（PostgreSQL 客戶端）和 Express.js 構(gòu)建一個(gè)基本的 CRUD 應(yīng)用程序，看看這些抽象在現(xiàn)實(shí)中如何閃耀——世界應(yīng)用。

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關(guān)鍵概念

在深入了解該應(yīng)用程序之前，我們先簡要討論一下主要概念：

1. 選項(xiàng)：對(duì)值的存在或不存在進(jìn)行建模（有或無）。
2. Either：表示計(jì)算可能成功（右）或失敗（左）。
3. Task：代表惰性異步計(jì)算。
4. Reader：將依賴項(xiàng)注入到計(jì)算中。
5. ReaderTaskEither：將 Reader、Task 和 Either 組合起來，用于具有依賴性和錯(cuò)誤處理的異步操作。

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設(shè)置項(xiàng)目

初始化項(xiàng)目

mkdir fp-ts-crud && cd fp-ts-crud
npm init -y
npm install express pg fp-ts io-ts
npm install --save-dev typescript @types/express ts-node-dev jest @types/jest ts-jest

設(shè)置打字稿

創(chuàng)建 tsconfig.json：

{
  "compilerOptions": {
    "target": "ES2020",
    "module": "CommonJS",
    "outDir": "dist",
    "strict": true,
    "esModuleInterop": true
  },
  "include": ["src/**/*"]
}

項(xiàng)目結(jié)構(gòu)

src/
  index.ts        # Entry point
  db.ts           # Database setup
  models/         # Data models and validation
  services/       # Business logic
  controllers/    # CRUD operations
  utils/          # fp-ts utilities
  errors/         # Custom error classes

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實(shí)施 CRUD 應(yīng)用程序

數(shù)據(jù)庫設(shè)置 (db.ts)

import { Pool } from 'pg';

export const pool = new Pool({
  user: 'postgres',
  host: 'localhost',
  database: 'fp_ts_crud',
  password: 'password',
  port: 5432,
});

定義模型和驗(yàn)證（models/User.ts）

import * as t from 'io-ts';
import { isRight } from 'fp-ts/Either';

export const User = t.type({
  id: t.number,
  name: t.string,
  email: t.string,
});

export const validateUser = (data: unknown): t.TypeOf<typeof User> | null => {
  const result = User.decode(data);
  return isRight(result) ? result.right : null;
};

自定義錯(cuò)誤處理（errors/AppError.ts）

export class AppError extends Error {
  constructor(public statusCode: number, public code: string, public message: string) {
    super(message);
    this.name = 'AppError';
  }
}

export const createAppError = (statusCode: number, code: string, message: string): AppError => {
  return new AppError(statusCode, code, message);
};

服務(wù)層（services/UserService.ts）

import { pool } from '../db';
import { ReaderTaskEither, right, left } from 'fp-ts/ReaderTaskEither';
import { pipe } from 'fp-ts/function';
import { createAppError, AppError } from '../errors/AppError';

type Dependencies = { db: typeof pool };
type User = { name: string; email: string };

export const createUser = (
  user: User
): ReaderTaskEither<Dependencies, AppError, string> => (deps) => async () => {
  try {
    const result = await deps.db.query(
      'INSERT INTO users (name, email) VALUES (, ) RETURNING id',
      [user.name, user.email]
    );
    return right(`User created with ID: ${result.rows[0].id}`);
  } catch (error) {
    return left(createAppError(500, 'USER_CREATION_FAILED', 'Failed to create user'));
  }
};

export const getUser = (
  id: number
): ReaderTaskEither<Dependencies, AppError, { id: number; name: string; email: string }> => (deps) => async () => {
  try {
    const result = await deps.db.query('SELECT * FROM users WHERE id = ', [id]);
    return result.rows[0]
      ? right(result.rows[0])
      : left(createAppError(404, 'USER_NOT_FOUND', 'User not found'));
  } catch {
    return left(createAppError(500, 'USER_FETCH_FAILED', 'Failed to fetch user'));
  }
};

CRUD 操作（控制器/UserController.ts）

import { pipe } from 'fp-ts/function';
import { createUser, getUser } from '../services/UserService';
import { pool } from '../db';
import { AppError } from '../errors/AppError';

const errorHandler = (err: unknown, res: express.Response): void => {
  if (err instanceof AppError) {
    res.status(err.statusCode).json({ error: { code: err.code, message: err.message } });
  } else {
    res.status(500).json({ error: { code: 'UNKNOWN_ERROR', message: 'An unexpected error occurred' } });
  }
};

export const createUserHandler = (req: express.Request, res: express.Response): void => {
  pipe(
    createUser(req.body),
    (task) => task({ db: pool }),
    (promise) =>
      promise.then((result) =>
        result._tag === 'Left'
          ? errorHandler(result.left, res)
          : res.json({ message: result.right })
      )
  );
};

export const getUserHandler = (req: express.Request, res: express.Response): void => {
  pipe(
    getUser(parseInt(req.params.id, 10)),
    (task) => task({ db: pool }),
    (promise) =>
      promise.then((result) =>
        result._tag === 'Left'
          ? errorHandler(result.left, res)
          : res.json(result.right)
      )
  );
};

Express API（index.ts）

import express from 'express';
import { createUserHandler, getUserHandler } from './controllers/UserController';

const app = express();
app.use(express.json());

// Routes
app.post('/users', createUserHandler);
app.get('/users/:id', getUserHandler);

// Start Server
app.listen(3000, () => {
  console.log('Server running on http://localhost:3000');
});

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使用 Docker 和 Docker Compose 運(yùn)行應(yīng)用程序

Dockerfile

# Stage 1: Build
FROM node:22 AS builder
WORKDIR /app
COPY package*.json .
RUN npm install
COPY . .
RUN npm run build

# Stage 2: Run
FROM node:22
WORKDIR /app
COPY --from=builder /app/dist ./dist
COPY package*.json ./
RUN npm install --production
CMD ["node", "dist/index.js"]

docker-compose.yml

version: '3.8'
services:
  db:
    image: postgres:15
    environment:
      POSTGRES_USER: postgres
      POSTGRES_PASSWORD: password
      POSTGRES_DB: fp_ts_crud
    ports:
      - "5432:5432"
    volumes:
      - db_data:/var/lib/postgresql/data
volumes:
  db_data:

運(yùn)行應(yīng)用程序 - 開發(fā)模式

# Start the database
docker-compose up -d

# Run the app
npx ts-node-dev src/index.ts

運(yùn)行應(yīng)用程序 - 生產(chǎn)模式

# Build the docker image
docker build -t fp-ts-crud-app .

# Start the database
docker-compose up -d

# Run the container
docker run -p 3000:3000 fp-ts-crud-app

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編寫測試

設(shè)置笑話

更新 package.json 腳本：

mkdir fp-ts-crud && cd fp-ts-crud
npm init -y
npm install express pg fp-ts io-ts
npm install --save-dev typescript @types/express ts-node-dev jest @types/jest ts-jest

示例測試 (__tests__/UserService.test.ts)

{
  "compilerOptions": {
    "target": "ES2020",
    "module": "CommonJS",
    "outDir": "dist",
    "strict": true,
    "esModuleInterop": true
  },
  "include": ["src/**/*"]
}

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結(jié)論

通過利用 fp-ts、Docker 和強(qiáng)大的錯(cuò)誤處理，我們構(gòu)建了一個(gè)功能齊全、可擴(kuò)展且可維護(hù)的 Node.js CRUD 應(yīng)用程序。使用函數(shù)式編程模式可以使您的代碼更加可預(yù)測和可靠，尤其是在處理異步工作流程時(shí)。

以上是Node.js 中使用 fp-ts 進(jìn)行函數(shù)式編程的詳細(xì)內(nèi)容。更多信息請(qǐng)關(guān)注PHP中文網(wǎng)其他相關(guān)文章！