go依赖注入库samber/do使用示例讲解

.
├── cmd
│   └── web
│       └── main.go
├── domain
│   └── user.go
├── go.mod
├── go.sum
└── user
    ├── handler.go
    ├── repository.go
    └── service.go

type (
	User struct {
		ID       string `json:"id"`
		Username string `json:"username"`
	}
	UserEntity struct {
		ID       string
		Username string
		Password string
	}
	UserRepository interface {
		FetchByUsername(ctx context.Context, username string) (*UserEntity, error)
	}
	UserService interface {
		FetchByUsername(ctx context.Context, username string) (*User, error)
	}
	UserHandler interface {
		FetchByUsername() http.HandlerFunc
	}
)

package main
import (
	"database/sql"
	"example/domain"
	"example/user"
	"fmt"
	"net/http"
	_ "github.com/lib/pq"
	"github.com/samber/do"
)
func main() {
	injector := do.New() // 1
	connStr := "user=root dbname=mydb"
	db, err := sql.Open("postgres", connStr) // 2
	if err != nil {
		panic(err)
	}
	defer db.Close()
	do.ProvideNamed[*sql.DB](injector, "user", func(i *do.Injector) (*sql.DB, error) {
		return db, nil
	}) // 3
    do.Provide(injector, user.NewRepository)
	do.Provide(injector, user.NewService)
	do.Provide(injector, user.NewHandler) // 4
	userHandler := do.MustInvoke[domain.UserHandler](injector) // 5
	http.Handle("/user", userHandler.FetchByUsername())
	fmt.Printf("Try run server at :%d\n", 8080)
	if err := http.ListenAndServe(":8080", nil); err != nil {
		fmt.Printf("Error: %v", err)
	}
}

package user
import (
	"context"
	"database/sql"
	"example/domain"
	"github.com/samber/do"
)
type repository struct {
	db *sql.DB
}
func (r *repository) FetchByUsername(ctx context.Context, username string) (*domain.UserEntity, error) {
	// use db here
}
// the return type of NewRepository should be interface, rather than the concrete type!
func NewRepository(i *do.Injector) (domain.UserRepository, error) {
	db := do.MustInvokeNamed[*sql.DB](i, "user")
	return &repository{db: db}, nil
}

package user
import (
	"context"
	"example/domain"
	"github.com/samber/do"
)
type service struct {
	repo domain.UserRepository
}
func (s *service) FetchByUsername(ctx context.Context, username string) (*domain.User, error) {
	// use repository here
}
func NewService(i *do.Injector) (domain.UserService, error) {
	repo := do.MustInvoke[domain.UserRepository](i)
	return &service{repo: repo}, nil
}

package user
import (
	"example/domain"
	"net/http"
	"github.com/samber/do"
)
type handler struct {
	svc domain.UserService
}
func (h *handler) FetchByUsername() http.HandlerFunc {
    // use service here
}
func NewHandler(i *do.Injector) (domain.UserHandler, error) {
	svc := do.MustInvoke[domain.UserService](i)
	return &handler{svc: svc}, nil
}