Connecting Gorm and Gin Golang

Question

I am trying to create an API with Go , gorm and gin . However, using a direct SQL query did work, but it became too cumbersome and I decided to leverage gorm which is fantastic. However after my implementation, I am unable to get the project up again and keep getting error

panic: runtime error: invalid memory address or nil pointer dereference [signal SIGSEGV: segmentation violation code=0x1 addr=0xb0 pc=0x137b606]

I have pasted my code with packages here. I would be glad if someone could point me to the issue.

PostgresDoa.go

package postgres

import (
    "fmt"
    "log"
    "net/http"

    "github.com/AdieOlami/bookstore_users-api/domain/users"
    "github.com/gin-gonic/gin"
    "github.com/jinzhu/gorm"
)

type Sever struct {
    DB     *gorm.DB
    Router *gin.Engine
}

func (server *Sever) Initialize(Dbdriver, DbUser, DbPassword, DbPort, DbHost, DbName string) {
    var err error

    if Dbdriver == "mysql" {
        DBURL := fmt.Sprintf("%s:%s@tcp(%s:%s)/%s?charset=utf8&parseTime=True&loc=Local", DbUser, DbPassword, DbHost, DbPort, DbName)
        server.DB, err = gorm.Open(Dbdriver, DBURL)
        if err != nil {
            fmt.Printf("Cannot connect to %s database", Dbdriver)
            log.Fatal("This is the error:", err)
        } else {
            fmt.Printf("We are connected to the %s database", Dbdriver)
        }
    }

    if Dbdriver == "postgres" {
        DBURL := fmt.Sprintf("host=%s port=%s user=%s dbname=%s sslmode=disable password=%s", DbHost, DbPort, DbUser, DbName, DbPassword)
        server.DB, err = gorm.Open(Dbdriver, DBURL)
        if err != nil {
            fmt.Printf("Cannot connect to %s database", Dbdriver)
            log.Fatal("This is the error:", err)
        } else {
            fmt.Printf("We are connected to the %s database", Dbdriver)
        }
    }

    server.DB.Debug().AutoMigrate(&users.User{}) //database migration
    server.Router = gin.Default()
}

func (server *Sever) Run(addr string) {
    fmt.Println("Listening to port 8080")
    log.Fatal(http.ListenAndServe(addr, server.Router))
}

UserDto.go

package users

import (
    "strings"

    "github.com/AdieOlami/bookstore_users-api/domain/base"
    "github.com/AdieOlami/bookstore_users-api/utils/errors"
    "github.com/jinzhu/gorm"
    uuid "github.com/satori/go.uuid"
)

type User struct {
    base.Base
    UserID    uuid.UUID `gorm:"type:uuid;column:userId;not null;" json:"userId"`
    FirstName string    `gorm:"size:255;not null;unique;column:firstName" json:"firstName"`
    LastName  string    `gorm:"size:255;not null;unique;column:lastName" json:"lastName"`
    Email     string    `gorm:"size:100;not null;unique;column:email" json:"email"`
}

func (user *User) Validate() *errors.Error {
    user.Email = strings.TrimSpace(strings.ToLower(user.Email))
    if user.Email == "" {
        return errors.NewBadRequestError("invalid email address")
    }
    return nil
}

func (user *User) SaveUser(db *gorm.DB) *errors.Error {

    var err error
    err = db.Debug().Create(&user).Error
    if err != nil {
        return errors.NewInteralServerError(err.Error())
    }
    return nil
}

UserService.go

package services

import (

    "github.com/AdieOlami/bookstore_users-api/domain/users"
    "github.com/AdieOlami/bookstore_users-api/utils/errors"
)

func (server *Server) CreateUser(user users.User) (*users.User, *errors.Error) {

    if err := user.Validate(); err != nil {
        return nil, err
    }

    if err := user.SaveUser(server.DB); err != nil {
        return nil, err
    }
    return &user, nil
}

UserController.go

package users

import (
    "net/http"
    "strconv"

    "github.com/AdieOlami/bookstore_users-api/domain/users"
    "github.com/AdieOlami/bookstore_users-api/services"
    "github.com/AdieOlami/bookstore_users-api/utils/errors"
    "github.com/gin-gonic/gin"
)

var (
    server = services.Server{}
)

// CREATE USER
func CreateUser(c *gin.Context) {
    var user users.User

    if err := c.ShouldBindJSON(&user); err != nil {
        // TODO: hnadle json error return bad request
        err := errors.NewBadRequestError("invalid json body")
        c.JSON(err.Status, err)
        // fmt.Println(err.Error())
        return
    }
    result, saveErr := server.CreateUser(user)
    if saveErr != nil {
        // TODO: handle user createing error
        c.JSON(saveErr.Status, saveErr)
        return
    }
    c.JSON(http.StatusCreated, result)
}

Routes.go

package app

import (
    "github.com/AdieOlami/bookstore_users-api/controllers/users"
    "github.com/AdieOlami/bookstore_users-api/database/postgres"
)

var (
    server = postgres.Sever{}
)

func initializeRoutes() {

    server.Router.POST("/users", users.CreateUser)
}

Application.go

package app

import (
    "os"

    "github.com/AdieOlami/bookstore_users-api/seed"

    _ "github.com/jinzhu/gorm/dialects/mysql"    //mysql database driver
    _ "github.com/jinzhu/gorm/dialects/postgres" //postgres database driver
)

func StartApplication() {

    server.Initialize(os.Getenv("DB_DRIVER"), os.Getenv("DB_USER"), os.Getenv("DB_PASSWORD"), os.Getenv("DB_PORT"), os.Getenv("DB_HOST"), os.Getenv("DB_NAME"))

    seed.Load(server.DB)
    server.Run(":8088")
    initializeRoutes()
}

in my Main.go

func main() {
    app.StartApplication()
}

Answer 1

As far as I can understand from your code. You declared below function in Services package whereas Server object is declared in the Postgres package. This causes dereferencing of pointer server *Server to an invalid address. you have to declare this function in posgres package.

func (server *Server) CreateUser(user users.User) (*users.User, *errors.Error) {

    if err := user.Validate(); err != nil {
        return nil, err
    }

    if err := user.SaveUser(server.DB); err != nil {
        return nil, err
    }
    return &user, nil
}