基于DDD的golang实践案例

Check the github repo for the updated code:
https://github.com/victorsteven/food-app-server

领域驱动设计模式算是比较热门的话题了。
领域驱动设计（DDD）是一种软件开发方法，通过将实现与不断演变的模型相连接，简化了开发人员面临的复杂性。
本文不会重点去解释Golang中实现DDD的相关理念，而是作者根据自己的研究对DDD的理解。

什么是DDD？
以下是考虑使用DDD的原因：

• 提供解决困难问题的原则和模式
• 将复杂的设计基于领域模型
• 在技术和领域专家之间发起创造性的协作，以迭代地完善解决领域问题的概念模型。

DDD包含4个层：

1. Domain：这是定义应用程序的域和业务逻辑的地方
2. Infrastructure：此层包含独立于我们的应用程序而存在的所有内容：外部库，数据库引擎等。
3. Application：该层用作域和界面层之间的通道。将请求从接口层发送到域层，由域层处理请求并返回响应。
4. Interface：该层包含与其他系统交互的所有内容，例如Web服务，RMI接口或Web应用程序以及批处理前端。

1

开始
我们将构建一个食物推荐API。
首先要做的是初始化依赖关系管理。我们将使用go.mod。在根目录（路径：food-app /）中，初始化go.mod：
go mod init food-app 项目的组织结构：

在该应用中，我们将使用postgres和redis数据库持久化数据。先定义一个含有连接信息的.env文件。
.env文件内容：

#Postgres
APP_ENV=local
API_PORT=8888
DB_HOST=127.0.0.1
DB_DRIVER=postgres
ACCESS_SECRET=98hbun98h
REFRESH_SECRET=786dfdbjhsb
DB_USER=steven
DB_PASSWORD=password
DB_NAME=food-app
DB_PORT=5432

#Mysql
#DB_HOST=127.0.0.1
#DB_DRIVER=mysql
#DB_USER=steven
#DB_PASSWORD=here
#DB_NAME=food-app
#DB_PORT=3306

#Postgres Test DB
TEST_DB_DRIVER=postgres
TEST_DB_HOST=127.0.0.1
TEST_DB_PASSWORD=password
TEST_DB_USER=steven
TEST_DB_NAME=food-app-test
TEST_DB_PORT=5432

#Redis
REDIS_HOST=127.0.0.1
REDIS_PORT=6379
REDIS_PASSWORD=

该文件应位于根目录中（路径：food-app /）

2

Domain 层
我们将首先考虑领域。
该域具有几种模式。其中一些是：实体，值，存储库，服务等。
由于我们在此处构建的应用比较简单，因此我们仅考虑两种域模式：实体和存储库。
实体
这是我们定义“Schema”的地方。
例如，我们可以定义用户的结构。将该实体视为域的蓝图。

package entity

import (
"food-app/infrastructure/security"
"github.com/badoux/checkmail"
"html"
"strings"
"time"
)

type User struct {
ID        uint64     `gorm:"primary_key;auto_increment" json:"id"`
FirstName string     `gorm:"size:100;not null;" json:"first_name"`
LastName  string     `gorm:"size:100;not null;" json:"last_name"`
Email     string     `gorm:"size:100;not null;unique" json:"email"`
Password  string     `gorm:"size:100;not null;" json:"password"`
CreatedAt time.Time  `gorm:"default:CURRENT_TIMESTAMP" json:"created_at"`
UpdatedAt time.Time  `gorm:"default:CURRENT_TIMESTAMP" json:"updated_at"`
DeletedAt *time.Time `json:"deleted_at,omitempty"`
}

type PublicUser struct {
ID        uint64 `gorm:"primary_key;auto_increment" json:"id"`
FirstName string `gorm:"size:100;not null;" json:"first_name"`
LastName  string `gorm:"size:100;not null;" json:"last_name"`
}

//BeforeSave is a gorm hook
func (u *User) BeforeSave() error {
hashPassword, err := security.Hash(u.Password)
if err != nil {
return err
}
u.Password = string(hashPassword)
return nil
}

type Users []User

//So that we dont expose the user's email address and password to the world
func (users Users) PublicUsers() []interface{} {
result := make([]interface{}, len(users))
for index, user := range users {
result[index] = user.PublicUser()
}
return result
}

//So that we dont expose the user's email address and password to the world
func (u *User) PublicUser() interface{} {
return &PublicUser{
ID:        u.ID,
FirstName: u.FirstName,
LastName:  u.LastName,
}
}

func (u *User) Prepare() {
u.FirstName = html.EscapeString(strings.TrimSpace(u.FirstName))
u.LastName = html.EscapeString(strings.TrimSpace(u.LastName))
u.Email = html.EscapeString(strings.TrimSpace(u.Email))
u.CreatedAt = time.Now()
u.UpdatedAt = time.Now()
}

func (u *User) Validate(action string) map[string]string {
var errorMessages = make(map[string]string)
var err error

switch strings.ToLower(action) {
case "update":
if u.Email == "" {
errorMessages["email_required"] = "email required"
}
if u.Email != "" {
if err = checkmail.ValidateFormat(u.Email); err != nil {
errorMessages["invalid_email"] = "email email"
}
}

case "login":
if u.Password == "" {
errorMessages["password_required"] = "password is required"
}
if u.Email == "" {
errorMessages["email_required"] = "email is required"
}
if u.Email != "" {
if err = checkmail.ValidateFormat(u.Email); err != nil {
errorMessages["invalid_email"] = "please provide a valid email"
}
}
case "forgotpassword":
if u.Email == "" {
errorMessages["email_required"] = "email required"
}
if u.Email != "" {
if err = checkmail.ValidateFormat(u.Email); err != nil {
errorMessages["invalid_email"] = "please provide a valid email"
}
}
default:
if u.FirstName == "" {
errorMessages["firstname_required"] = "first name is required"
}
if u.LastName == "" {
errorMessages["lastname_required"] = "last name is required"
}
if u.Password == "" {
errorMessages["password_required"] = "password is required"
}
if u.Password != "" &amp;&amp; len(u.Password) < 6 {
errorMessages["invalid_password"] = "password should be at least 6 characters"
}
if u.Email == "" {
errorMessages["email_required"] = "email is required"
}
if u.Email != "" {
if err = checkmail.ValidateFormat(u.Email); err != nil {
errorMessages["invalid_email"] = "please provide a valid email"
}
}
}
return errorMessages
}

在上面的文件中，定义了包含用户信息的用户结构，我们还添加了帮助程序功能，这些功能将验证和清理输入。调用了一种哈希方法，该方法用于哈希密码。这是在基础结构层中定义的。
定义 food 实体时采用相同的方法。
存储库
存储库定义了基础结构实现的方法的集合。这描绘了与给定数据库或第三方API交互的方法数量。
user 存储库如下所示：

package repository

import (
"food-app/domain/entity"
)

type UserRepository interface {
SaveUser(*entity.User) (*entity.User, map[string]string)
GetUser(uint64) (*entity.User, error)
GetUsers() ([]entity.User, error)
GetUserByEmailAndPassword(*entity.User) (*entity.User, map[string]string)
}

方法在接口中定义。这些方法稍后将在基础结构层中实现。
food 库几乎相同。

3

Infrastructure 层
该层实现存储库中定义的方法。这些方法与数据库或第三方API交互。本文中仅考虑数据库交互。

我们可以看到 user 存储库实现如下所示：

package persistence

import (
"errors"
"food-app/domain/entity"
"food-app/domain/repository"
"food-app/infrastructure/security"
"github.com/jinzhu/gorm"
"golang.org/x/crypto/bcrypt"
"strings"
)

type UserRepo struct {
db *gorm.DB
}

func NewUserRepository(db *gorm.DB) *UserRepo {
return &UserRepo{db}
}
//UserRepo implements the repository.UserRepository interface
var _ repository.UserRepository = &UserRepo{}

func (r *UserRepo) SaveUser(user *entity.User) (*entity.User, map[string]string) {
dbErr := map[string]string{}
err := r.db.Debug().Create(&user).Error
if err != nil {
//If the email is already taken
if strings.Contains(err.Error(), "duplicate") || strings.Contains(err.Error(), "Duplicate") {
dbErr["email_taken"] = "email already taken"
return nil, dbErr
}
//any other db error
dbErr["db_error"] = "database error"
return nil, dbErr
}
return user, nil
}

func (r *UserRepo) GetUser(id uint64) (*entity.User, error) {
var user entity.User
err := r.db.Debug().Where("id = ?", id).Take(&user).Error
if err != nil {
return nil, err
}
if gorm.IsRecordNotFoundError(err) {
return nil, errors.New("user not found")
}
return &user, nil
}

func (r *UserRepo) GetUsers() ([]entity.User, error) {
var users []entity.User
err := r.db.Debug().Find(&users).Error
if err != nil {
return nil, err
}
if gorm.IsRecordNotFoundError(err) {
return nil, errors.New("user not found")
}
return users, nil
}

func (r *UserRepo) GetUserByEmailAndPassword(u *entity.User) (*entity.User, map[string]string) {
var user entity.User
dbErr := map[string]string{}
err := r.db.Debug().Where("email = ?", u.Email).Take(&user).Error
if gorm.IsRecordNotFoundError(err) {
dbErr["no_user"] = "user not found"
return nil, dbErr
}
if err != nil {
dbErr["db_error"] = "database error"
return nil, dbErr
}
//Verify the password
err = security.VerifyPassword(user.Password, u.Password)
if err != nil && err == bcrypt.ErrMismatchedHashAndPassword {
dbErr["incorrect_password"] = "incorrect password"
return nil, dbErr
}
return &user, nil
}

可以看到我们实现了存储库中定义的方法。使用实现了UserRepository接口的UserRepo结构可以做到这一点，如下行所示：

//UserRepo implements the repository.UserRepository interface
var _ repository.UserRepository = &UserRepo{}

因此，我们通过创建包含以下内容的db.go文件来配置数据库：

package persistence

import (
"fmt"
"food-app/domain/entity"
"food-app/domain/repository"
"github.com/jinzhu/gorm"
_ "github.com/jinzhu/gorm/dialects/postgres"
)

type Repositories struct {
User repository.UserRepository
Food repository.FoodRepository
db   *gorm.DB
}

func NewRepositories(Dbdriver, DbUser, DbPassword, DbPort, DbHost, DbName string) (*Repositories, error) {
DBURL := fmt.Sprintf("host=%s port=%s user=%s dbname=%s sslmode=disable password=%s", DbHost, DbPort, DbUser, DbName, DbPassword)
db, err := gorm.Open(Dbdriver, DBURL)
if err != nil {
return nil, err
}
db.LogMode(true)

return &Repositories{
User: NewUserRepository(db),
Food: NewFoodRepository(db),
db:   db,
}, nil
}

//closes the  database connection
func (s *Repositories) Close() error {
return s.db.Close()
}

//This migrate all tables
func (s *Repositories) Automigrate() error {
return s.db.AutoMigrate(&entity.User{}, &entity.Food{}).Error
}

在上面的文件中，我们定义了Repositories结构，该结构保存了应用中的所有存储库。我们有 user 和 food 库。该存储库还具有一个db实例，该实例被传递给 user 和 food（即NewUserRepository和NewFoodRepository）的“constructors”。

4

Application 层
我们已经在域中定义了API业务逻辑。该层连接 domain 和 interfaces 层。
以下是 user 的应用层：

package application

import (
"food-app/domain/entity"
"food-app/domain/repository"
)

type userApp struct {
us repository.UserRepository
}

//UserApp implements the UserAppInterface
var _ UserAppInterface = &userApp{}

type UserAppInterface interface {
SaveUser(*entity.User) (*entity.User, map[string]string)
GetUsers() ([]entity.User, error)
GetUser(uint64) (*entity.User, error)
GetUserByEmailAndPassword(*entity.User) (*entity.User, map[string]string)
}

func (u *userApp) SaveUser(user *entity.User) (*entity.User, map[string]string) {
return u.us.SaveUser(user)
}

func (u *userApp) GetUser(userId uint64) (*entity.User, error) {
return u.us.GetUser(userId)
}

func (u *userApp) GetUsers() ([]entity.User, error) {
return u.us.GetUsers()
}

func (u *userApp) GetUserByEmailAndPassword(user *entity.User) (*entity.User, map[string]string) {
return u.us.GetUserByEmailAndPassword(user)
}

上面有保存和检索用户数据的方法。UserApp结构具有UserRepository接口，从而可以调用用户存储库方法。

5

Interfaces 层
接口是处理HTTP请求和响应的层。这里我们收到身份验证，与用户相关的内容和与食品相关的内容的传入请求。

用户处理
我们定义了保存用户，获取所有用户和获取特定用户的方法。这些可以在user_handler.go文件中找到。

package interfaces

import (
"food-app/application"
"food-app/domain/entity"
"food-app/infrastructure/auth"
"github.com/gin-gonic/gin"
"net/http"
"strconv"
)

//Users struct defines the dependencies that will be used
type Users struct {
us application.UserAppInterface
rd auth.AuthInterface
tk auth.TokenInterface
}

//Users constructor
func NewUsers(us application.UserAppInterface, rd auth.AuthInterface, tk auth.TokenInterface) *Users {
return &Users{
us: us,
rd: rd,
tk: tk,
}
}

func (s *Users) SaveUser(c *gin.Context) {
var user entity.User
if err := c.ShouldBindJSON(&user); err != nil {
c.JSON(http.StatusUnprocessableEntity, gin.H{
"invalid_json": "invalid json",
})
return
}
//validate the request:
validateErr := user.Validate("")
if len(validateErr) > 0 {
c.JSON(http.StatusUnprocessableEntity, validateErr)
return
}
newUser, err := s.us.SaveUser(&user)
if err != nil {
c.JSON(http.StatusInternalServerError, err)
return
}
c.JSON(http.StatusCreated, newUser.PublicUser())
}

func (s *Users) GetUsers(c *gin.Context) {
users := entity.Users{} //customize user
var err error
//us, err = application.UserApp.GetUsers()
users, err = s.us.GetUsers()
if err != nil {
c.JSON(http.StatusInternalServerError, err.Error())
return
}
c.JSON(http.StatusOK, users.PublicUsers())
}

func (s *Users) GetUser(c *gin.Context) {
userId, err := strconv.ParseUint(c.Param("user_id"), 10, 64)
if err != nil {
c.JSON(http.StatusBadRequest, err.Error())
return
}
user, err := s.us.GetUser(userId)
if err != nil {
c.JSON(http.StatusInternalServerError, err.Error())
return
}
c.JSON(http.StatusOK, user.PublicUser())
}

观察到返回用户时，我们仅返回一个公共用户（在实体中定义）。公共用户没有敏感的用户详细信息，例如电子邮件和密码。
授权处理
login_handler负责登录，注销和刷新令牌方法。在各自文件中定义的某些方法在此文件中被调用。最好在它们的文件路径之后在存储库中检出它们。

package interfaces

import (
"fmt"
"food-app/application"
"food-app/domain/entity"
"food-app/infrastructure/auth"
"github.com/dgrijalva/jwt-go"
"github.com/gin-gonic/gin"
"net/http"
"os"
"strconv"
)

type Authenticate struct {
us application.UserAppInterface
rd auth.AuthInterface
tk auth.TokenInterface
}

//Authenticate constructor
func NewAuthenticate(uApp application.UserAppInterface, rd auth.AuthInterface, tk auth.TokenInterface) *Authenticate {
return &Authenticate{
us: uApp,
rd: rd,
tk: tk,
}
}

func (au *Authenticate) Login(c *gin.Context) {
var user *entity.User
var tokenErr = map[string]string{}

if err := c.ShouldBindJSON(&user); err != nil {
c.JSON(http.StatusUnprocessableEntity, "Invalid json provided")
return
}
//validate request:
validateUser := user.Validate("login")
if len(validateUser) > 0 {
c.JSON(http.StatusUnprocessableEntity, validateUser)
return
}
u, userErr := au.us.GetUserByEmailAndPassword(user)
if userErr != nil {
c.JSON(http.StatusInternalServerError, userErr)
return
}
ts, tErr := au.tk.CreateToken(u.ID)
if tErr != nil {
tokenErr["token_error"] = tErr.Error()
c.JSON(http.StatusUnprocessableEntity, tErr.Error())
return
}
saveErr := au.rd.CreateAuth(u.ID, ts)
if saveErr != nil {
c.JSON(http.StatusInternalServerError, saveErr.Error())
return
}
userData := make(map[string]interface{})
userData["access_token"] = ts.AccessToken
userData["refresh_token"] = ts.RefreshToken
userData["id"] = u.ID
userData["first_name"] = u.FirstName
userData["last_name"] = u.LastName

c.JSON(http.StatusOK, userData)
}

func (au *Authenticate) Logout(c *gin.Context) {
//check is the user is authenticated first
metadata, err := au.tk.ExtractTokenMetadata(c.Request)
if err != nil {
c.JSON(http.StatusUnauthorized, "Unauthorized")
return
}
//if the access token exist and it is still valid, then delete both the access token and the refresh token
deleteErr := au.rd.DeleteTokens(metadata)
if deleteErr != nil {
c.JSON(http.StatusUnauthorized, deleteErr.Error())
return
}
c.JSON(http.StatusOK, "Successfully logged out")
}

//Refresh is the function that uses the refresh_token to generate new pairs of refresh and access tokens.
func (au *Authenticate) Refresh(c *gin.Context) {
mapToken := map[string]string{}
if err := c.ShouldBindJSON(&mapToken); err != nil {
c.JSON(http.StatusUnprocessableEntity, err.Error())
return
}
refreshToken := mapToken["refresh_token"]

//verify the token
token, err := jwt.Parse(refreshToken, func(token *jwt.Token) (interface{}, error) {
//Make sure that the token method conform to "SigningMethodHMAC"
if _, ok := token.Method.(*jwt.SigningMethodHMAC); !ok {
return nil, fmt.Errorf("unexpected signing method: %v", token.Header["alg"])
}
return []byte(os.Getenv("REFRESH_SECRET")), nil
})
//any error may be due to token expiration
if err != nil {
c.JSON(http.StatusUnauthorized, err.Error())
return
}
//is token valid?
if _, ok := token.Claims.(jwt.Claims); !ok && !token.Valid {
c.JSON(http.StatusUnauthorized, err)
return
}
//Since token is valid, get the uuid:
claims, ok := token.Claims.(jwt.MapClaims)
if ok && token.Valid {
refreshUuid, ok := claims["refresh_uuid"].(string) //convert the interface to string
if !ok {
c.JSON(http.StatusUnprocessableEntity, "Cannot get uuid")
return
}
userId, err := strconv.ParseUint(fmt.Sprintf("%.f", claims["user_id"]), 10, 64)
if err != nil {
c.JSON(http.StatusUnprocessableEntity, "Error occurred")
return
}
//Delete the previous Refresh Token
delErr := au.rd.DeleteRefresh(refreshUuid)
if delErr != nil { //if any goes wrong
c.JSON(http.StatusUnauthorized, "unauthorized")
return
}
//Create new pairs of refresh and access tokens
ts, createErr := au.tk.CreateToken(userId)
if createErr != nil {
c.JSON(http.StatusForbidden, createErr.Error())
return
}
//save the tokens metadata to redis
saveErr := au.rd.CreateAuth(userId, ts)
if saveErr != nil {
c.JSON(http.StatusForbidden, saveErr.Error())
return
}
tokens := map[string]string{
"access_token":  ts.AccessToken,
"refresh_token": ts.RefreshToken,
}
c.JSON(http.StatusCreated, tokens)
} else {
c.JSON(http.StatusUnauthorized, "refresh token expired")
}
}

6

运行程序
我们测试一下该应用。我们将连接路由，连接到数据库并启动应用程序。
在根目录中定义的main.go文件中完成。

package main

import (
"food-app/infrastructure/auth"
"food-app/infrastructure/persistence"
"food-app/interfaces"
"food-app/interfaces/fileupload"
"food-app/interfaces/middleware"
"github.com/gin-gonic/gin"
"github.com/joho/godotenv"
"log"
"os"
)

func init() {
//To load our environmental variables.
if err := godotenv.Load(); err != nil {
log.Println("no env gotten")
}
}

func main() {

dbdriver := os.Getenv("DB_DRIVER")
host := os.Getenv("DB_HOST")
password := os.Getenv("DB_PASSWORD")
user := os.Getenv("DB_USER")
dbname := os.Getenv("DB_NAME")
port := os.Getenv("DB_PORT")

//redis details
redis_host := os.Getenv("REDIS_HOST")
redis_port := os.Getenv("REDIS_PORT")
redis_password := os.Getenv("REDIS_PASSWORD")

services, err := persistence.NewRepositories(dbdriver, user, password, port, host, dbname)
if err != nil {
panic(err)
}
defer services.Close()
services.Automigrate()

redisService, err := auth.NewRedisDB(redis_host, redis_port, redis_password)
if err != nil {
log.Fatal(err)
}

tk := auth.NewToken()
fd := fileupload.NewFileUpload()

users := interfaces.NewUsers(services.User, redisService.Auth, tk)
foods := interfaces.NewFood(services.Food, services.User, fd, redisService.Auth, tk)
authenticate := interfaces.NewAuthenticate(services.User, redisService.Auth, tk)

r := gin.Default()
r.Use(middleware.CORSMiddleware()) //For CORS

//user routes
r.POST("/users", users.SaveUser)
r.GET("/users", users.GetUsers)
r.GET("/users/:user_id", users.GetUser)

//post routes
r.POST("/food", middleware.AuthMiddleware(), middleware.MaxSizeAllowed(8192000), foods.SaveFood)
r.PUT("/food/:food_id", middleware.AuthMiddleware(), middleware.MaxSizeAllowed(8192000), foods.UpdateFood)
r.GET("/food/:food_id", foods.GetFoodAndCreator)
r.DELETE("/food/:food_id", middleware.AuthMiddleware(), foods.DeleteFood)
r.GET("/food", foods.GetAllFood)

//authentication routes
r.POST("/login", authenticate.Login)
r.POST("/logout", authenticate.Logout)
r.POST("/refresh", authenticate.Refresh)

//Starting the application
app_port := os.Getenv("PORT") //using heroku host
if app_port == "" {
app_port = "8888" //localhost
}
log.Fatal(r.Run(":"+app_port))
}

其中的中间件也是定义在 interfaces 层。

package middleware

import (
"bytes"
"food-app/infrastructure/auth"
"github.com/gin-gonic/gin"
"io/ioutil"
"net/http"
)

func AuthMiddleware() gin.HandlerFunc {
return func(c *gin.Context) {
err := auth.TokenValid(c.Request)
if err != nil {
c.JSON(http.StatusUnauthorized, gin.H{
"status": http.StatusUnauthorized,
"error":  err.Error(),
})
c.Abort()
return
}
c.Next()
}
}

func CORSMiddleware() gin.HandlerFunc {
return func(c *gin.Context) {
c.Writer.Header().Set("Access-Control-Allow-Origin", "*")
c.Writer.Header().Set("Access-Control-Allow-Credentials", "true")
c.Writer.Header().Set("Access-Control-Allow-Headers", "Content-Type, Content-Length, Accept-Encoding, X-CSRF-Token, Authorization, accept, origin, Cache-Control, X-Requested-With")
c.Writer.Header().Set("Access-Control-Allow-Methods", "POST, OPTIONS, GET, PUT, PATCH, DELETE")

if c.Request.Method == "OPTIONS" {
c.AbortWithStatus(204)
return
}
c.Next()
}
}

//Avoid a large file from loading into memory
//If the file size is greater than 8MB dont allow it to even load into memory and waste our time.
func MaxSizeAllowed(n int64) gin.HandlerFunc {
return func(c *gin.Context) {
c.Request.Body = http.MaxBytesReader(c.Writer, c.Request.Body, n)
buff, errRead := c.GetRawData()
if errRead != nil {
//c.JSON(http.StatusRequestEntityTooLarge,"too large")
c.JSON(http.StatusRequestEntityTooLarge, gin.H{
"status":     http.StatusRequestEntityTooLarge,
"upload_err": "too large: upload an image less than 8MB",
})
c.Abort()
return
}
buf := bytes.NewBuffer(buff)
c.Request.Body = ioutil.NopCloser(buf)
}
}

我们现在可以使用以下命令运行该应用：
go run main.go