【クリーンアーキテクチャの導入】Go言語でのAPI開発 | 実践的な学習から実装まで③

myApiProject
    ┗cmd
        ┗main.go
    ┗internal
        ┗domain
            ┗user.go
        ┗usecase
            ┗user_usecase.go
        ┗handler
            ┗user_handler.go
        ┗repository
            ┗user_repository.go
        ┗infrastructure
            ┗database.go
    ┗pkg
        ┗router
            ┗router.go

package main

import (
	"log"
	"myApiProject/internal/infrastructure"
	"myApiProject/pkg/router"
	"net/http"
)

func main() {
	db := infrastructure.InitDB()
	defer db.Close()
	router := router.NewRouter(db)
	log.Fatal(http.ListenAndServe(":8080", router))
}

package domain

type User struct {
    UserID   int
    Name     string
    Email    string
    Password string
}

package usecase

import (
	"myApiProject/internal/domain"
	"myApiProject/internal/repository"
)

type UserUseCase struct {
	repo repository.UserRepository
}

func NewUserUseCase(repo repository.UserRepository) *UserUseCase {
	return &UserUseCase{repo: repo}
}

func (uc *UserUseCase) GetUser(userID string) (*domain.User, error) {
	return uc.repo.FindByID(userID)
}

package handler

import (
	"encoding/json"
	"myApiProject/internal/usecase"
	"net/http"
)

type UserHandler struct {
	useCase *usecase.UserUseCase
}

func NewUserHandler(useCase *usecase.UserUseCase) *UserHandler {
	return &UserHandler{useCase: useCase}
}

func (h *UserHandler) GetUser(w http.ResponseWriter, r *http.Request) {
	userID := r.URL.Query().Get("user_id")
	if userID == "" {
		http.Error(w, "User ID is missing", http.StatusBadRequest)
		return
	}

	user, err := h.useCase.GetUser(userID)
	if err != nil {
		http.Error(w, "Internal server error", http.StatusInternalServerError)
		return
	}

	json.NewEncoder(w).Encode(user)
}

package repository

import (
	"database/sql"
	"myApiProject/internal/domain"
)

type UserRepository struct {
	db *sql.DB
}

func NewUserRepository(db *sql.DB) *UserRepository {
	return &UserRepository{db: db}
}

func (r *UserRepository) FindByID(userID string) (*domain.User, error) {
	user := &domain.User{}
	err := r.db.QueryRow("SELECT user_id, name, email, password FROM Users WHERE user_id = ?", userID).Scan(&user.UserID, &user.Name, &user.Email, &user.Password)
	if err != nil {
		return nil, err
	}
	return user, nil
}

package infrastructure

import (
	"database/sql"
	"log"

	_ "github.com/go-sql-driver/mysql"
)

func InitDB() *sql.DB {
	db, err := sql.Open("mysql", "apiuser:apipassword@tcp(localhost:3306)/apidb")
	if err != nil {
		log.Fatal(err)
	}

	if err = db.Ping(); err != nil {
		log.Fatal(err)
	}

	return db
}

package router

import (
	"database/sql"
	"myApiProject/internal/handler"
	"myApiProject/internal/repository"
	"myApiProject/internal/usecase"
	"net/http"
)

func NewRouter(db *sql.DB) *http.ServeMux {
	repo := repository.NewUserRepository(db)
	useCase := usecase.NewUserUseCase(*repo)
	userHandler := handler.NewUserHandler(useCase)

	router := http.NewServeMux()
	router.HandleFunc("/user", userHandler.GetUser)
	return router
}

myApiProject
    ┗cmd
        ┗main.go				// ルーターとデータベースの初期化
    ┗internal
        ┗domain
            ┗user.go			// エンティティの定義
        ┗usecase
            ┗user_usecase.go		// データの検証やビジネスルールの適用
        ┗handler
            ┗user_handler.go		// リクエストを処理し、適切なレスポンスを返答
        ┗repository
            ┗user_repository.go	// データの取得や登録、更新などの実行
        ┗infrastructure
            ┗database.go		// DBへの接続、初期化
    ┗pkg
        ┗router
            ┗router.go			// ルーティング(URL)の定義