README.md

File Sharing with Golang

This project is designed to help beginners learn backend development using Golang. It covers a wide range of beginner concepts and techniques in the backend development space. Topics covered in this project include:

• Setting up a database connection using GORM
• Building REST APIs using the GIN framework
• Implementing CRUD operations using GORM for data manipulation
• Understanding and implementing table associations with foreign keys
• Efficiently populating fields using the Preload() function
• Serialization of data into JSON format
• Customizing response and error formats for better user experience
• Uploading files to Cloudinary for storage and retrieval
• Utilizing .env files for secure configuration management
• Following Clean Architecture principles for maintainability and scalability

---

Generate the go.mod file with the command go mod init go-crud go-crud here is the package name. After this run the command go mod tidy to add module requirements and generate sum files. go mod tidy also cleans the unused packages.

main.go contains main function which is the entry point of the application. It contains the routes of the application.

func main() {
	SetupAppRouter()
}

func SetupAppRouter() *gin.Engine {

	db := configs.Connection()

	router := gin.Default()

	gin.SetMode(gin.TestMode)

	api := router.Group("api/v1")

	routes.InitAuthRoutes(db, api)

	return router
}

The InitAuthRoutes takes two parameters db *gorm.DB and route *gin.RouterGroup.

func InitAuthRoutes(db *gorm.DB, route *gin.RouterGroup) {
    // creates the new instance of the Repository
	loginRepository := loginAuth.NewRepositoryLogin(db)

    // creates the new instance of the Service
	loginService := loginAuth.NewServiceLogin(loginRepository)

    // creates the new instance of the Handler
	loginHandler := loginHandler.NewHandlerLogin(loginService)

	route.POST("/login", loginHandler.LoginHandler)
}

The call flow for the application looks like

loginHandler    ->  loginService        ->      loginRepository
(parse request)     (LoginInput to UserEntity)   (perform DB operations)

• The loginHandler validates the request body and parse the request body into LoginInput struct. Now, if any errors occur, it returns the response with respective error message. Now, the loginHandler calls the loginService that takes the argument LoginInput.
• The loginService parses the LoginInput and uses the values to parse it into the UserEntity struct. The loginService calls the loginRepository that takes the argument UserEntity.
• The loginRepository has the access to the *gorm.DB. It performs the operation with the database and returns either of the (*model.EntityUsers, string) value based upon the success and failure of the operation.

Why are we using *pointer in the return type instead of value of the object?

Snippet example:

// why are we using this
func (r *repository) LoginRepository(input *models.UserEntity) (*models.UserEntity, int) {}

// instead of this
func (r *repository) LoginRepository(input models.UserEntity) (models.UserEntity, int) {}

In the first function, the return type is *models.UserEntity. It means it returns the pointer to the UserEnitity type. This allows us to modify the object directly, and any changes made to the returned object will affect the original object. This can be useful because we want to maintain a single shared instance of UserEnitity and to avoid unnecessary object copies.

In the second function, the return type is models.UserEntity. It means new object will be created each time you call the function, and any modifications made to the returned UserEntity object will not affect the original object passed as an argument. Note: This can be useful if you want to create multiple independent instances of UserEntity

Relationship

type FileEntity struct {
	ID        uint       `gorm:"primary_key" json:"id"`
	Type      string     `gorm:"not null" json:"type"`
	Name      string     `gorm:"not null" json:"name"`
	Url       string     `gorm:"not null" json:"url"`
	AccessKey string     `gorm:"" json:"access_key"`
	CreatedAt time.Time  `gorm:"" json:"createdAt"`
	UpdatedAt time.Time  `gorm:"" json:"updatedAt"`
	UserID    uint       `gorm:"foreignkey:UserRefer" json:"-"`
	User      UserEntity `gorm:"foreignkey:UserRefer" json:"user"`
}

type UserEntity struct {
	ID        uint   `gorm:"primary_key"`
	Username  string `gorm:"column:username;unique;not null"`
	Email     string `gorm:"column:email;unique;not null"`
	Image     string `gorm:"column:image"`
	Password  string `gorm:"column:password;not null" json:"-"`
	CreatedAt time.Time
	UpdatedAt time.Time
}

In the FileEntity struct, there is a foreign key field UserID of type uint. This field establishes the relationship between FileEntity and UserEntity using the foreign key constraint. The foreign key constraint ensures data integrity between the two tables when inserting or updating records.

Populating Associations

To populate the foreign key value in GORM based on the given context, we can use the Preload function with the relationship defined in the FileModel struct. Here's an example:

var files []models.FileModel
db.Select("*").Where("user_id=?", userId).Find(&files)
db.Preload("User").Find(&files)

In this case, the Preload("User") call specifies that we want to load the associated UserEntity record using the foreign key relationship defined in the FileModel struct. This will populate the User field in the FileModel instance with the associated UserEntity.

Utilities

In the file utils/json.go the function definition looks like

func ObjectToJson[T any](object interface{}, data *T) {
	// 
}

Which means the function ObjectToJson takes the parameter of type T and returns the pointer to address of same type.

Usecase:

var data register.RegisterResponse
utils.ObjectToJson(resultLogin, &data)

So, when we want to convert the object of type RegisterResponse to json. We call the function ObjectToJson and it maps resultLogin to the object of type register.RegisterResponse and assign the value to data.