我试着用jwt atuhorize，但我得到的问题是，当我检查电子邮件与价值电子邮件从索赔我得到错误500。这个问题是因为数据库还没有准备好。
这是密码

• • 包路由**

package route

import (
    "go_fiber/controller"
    "go_fiber/middleware"

    "github.com/gofiber/fiber/v2"
)

func RouteInit(app *fiber.App, userController controller.UserController) {
    app.Get("/users", middleware.AuthMiddleware, userController.FindAll)
    app.Post("/login", userController.Login)
}

• • 打包应用程序**

package app

import (
    "database/sql"
    "fmt"
    "go_fiber/helper"
    "os"
    "time"

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

func NewDB() *sql.DB {

    var (   
        username = envVariable("DB_USERNAME")
        password = envVariable("DB_PASSWORD")
        host = envVariable("DB_HOST")
        port = envVariable("DB_PORT")
        db_name = envVariable("DB_NAME")
    )

    dns := fmt.Sprintf("%s:%s@tcp(%s:%s)/%s?parseTime=True", username, password, host, port, db_name)

    db, err := sql.Open("mysql", dns)
    if err != nil {
        panic(err)
    }

    db.SetMaxIdleConns(10)
    db.SetMaxOpenConns(100)
    db.SetConnMaxIdleTime(5 * time.Minute)
    db.SetConnMaxLifetime(60 * time.Minute)

    return db
}

• • 程序包主**

package main

import (
    "go_fiber/app"
    "go_fiber/controller"
    "go_fiber/exception"
    "go_fiber/repository"
    "go_fiber/route"
    "go_fiber/service"

    "github.com/go-playground/validator/v10"
    "github.com/gofiber/fiber/v2"
)

func main(){

    var db = app.NewDB()
    app := fiber.New()
    app.Use(func(c *fiber.Ctx) error {
        defer func() {
            if err := recover(); err != nil {
                exception.ErrorHandler(c, err)
            }
        }()
    
        return c.Next()
    })

    validator := validator.New()
    userRepository := repository.NewUserRepository()
    userService := service.NewUserService(userRepository, db, validator)
    userController := controller.NewUserController(userService)
    
    route.RouteInit(app, userController)

    app.Listen(":3000")
}

• • 软件包中间件**

package middleware

import (
    "database/sql"
    "errors"
    "fmt"
    "go_fiber/exception"
    "log"
    "os"
    "time"

    "github.com/gofiber/fiber/v2"
    "github.com/golang-jwt/jwt/v4"
)

func AuthMiddleware(c *fiber.Ctx) error{
    tokenString := c.Cookies("Authorization") 

    log.Printf("(middleware) token : %v", tokenString)

    if tokenString == "" {
        panic(exception.NewUserUnauthorized(errors.New("User Unauthorized").Error()))
    }

    token, err := jwt.Parse(tokenString, func(token *jwt.Token) (interface{}, error) {
        if _, ok := token.Method.(*jwt.SigningMethodHMAC); !ok {
            return nil, fmt.Errorf("unexpected signing method :%v", token.Header["sub"])
        }

        return []byte(os.Getenv("SECRET")), nil
    })

    log.Printf("(middleware) token : %v", token)
    log.Printf("(middleware) error : %v", err)

    if claims, ok := token.Claims.(jwt.MapClaims); ok && token.Valid {
        if float64(time.Now().Unix()) > claims["exp"].(float64) {
            panic(exception.NewUserUnauthorized(errors.New("User Unauthorized").Error()))
        }

        log.Printf("(middleware) claims : %v", claims)
        log.Printf("(middleware) ok : %v", ok)
        
        var DB *sql.DB

        tx, err := DB.Begin()
        
        log.Printf("(middleware) tx : %v", tx)
        log.Printf("(middleware) error : %v", err)
        
        query :=`
            SELECT email FROM users 
            WHERE email = ? 
            LIMIT 1
        `
        log.Printf("(middleware) query : %v", query)

        user, err := tx.QueryContext(c.Context(), query, claims["sub"])

        log.Printf("(middleware) user  : %v", user)
        log.Printf("(middleware) error : %v", err)
        

        if err != nil {
            panic(exception.NewUserUnauthorized(errors.New("User Unauthorized").Error()))
        }

        c.Locals("user", user)
        c.Next()
    }else {
        panic(exception.NewUserUnauthorized(errors.New("User Unauthorized").Error()))
    }

    return nil
}

这部分是问题代码

var DB *sql.DB
tx, err := DB.Begin()   
log.Printf("(middleware) tx : %v", tx) // No detect in terminal

这是日志的输出

2023/02/12 10:00:04 (middleware) token : eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJleHAiOjE2NzYxNzEzOTIsInN1YiI6IkphZmFyQGdtYWlsLmNvbSJ9.6nn_IaNACHfe7flFMOXfj1ygZS-U_yrnU_Gvjn8xCp8
2023/02/12 10:00:04 (middleware) token : &{eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJleHAiOjE2NzYxNzEzOTIsInN1YiI6IkphZmFyQGdtYWlsLmNvbSJ9.6nn_IaNACHfe7flFMOXfj1ygZS-U_yrnU_Gvjn8xCp8 0xc0000a6780 map[alg:HS256 typ:JWT] map[exp:1.676171392e+09 sub:John@gmail.com] 6nn_IaNACHfe7flFMOXfj1ygZS-U_yrnU_Gvjn8xCp8 true}
2023/02/12 10:00:04 (middleware) error : <nil>
2023/02/12 10:00:04 (middleware) claims : map[exp:1.676171392e+09 sub:John@gmail.com]
2023/02/12 10:00:04 (middleware) ok : true

那么，如何解决这个问题，以访问数据库，如果不同的包？