How to Pass Database Connection into Controllers in Golang

controllers.go

package controllers

import (
	"fmt"
	"net/http"

	"github.com/techinscribed/repository-db/models"
)

// BaseHandler will hold everything that controller needs
type BaseHandler struct {
	userRepo models.UserRepository
}

// NewBaseHandler returns a new BaseHandler
func NewBaseHandler(userRepo models.UserRepository) *BaseHandler {
	return &BaseHandler{
		userRepo: userRepo,
	}
}

// HelloWorld returns Hello, World
func (h *BaseHandler) HelloWorld(w http.ResponseWriter, r *http.Request) {
	if user, err := h.userRepo.FindByID(1); err != nil {
		fmt.Println("Error", user)
	}

	w.Write([]byte("Hello, World"))
}

global_db.go

package sqldb

import "database/sql"

// DB is a global variable to hold db connection
var DB *sql.DB

// ConnectDB opens a connection to the database
func ConnectDB() {
	db, err := sql.Open("mysql", "username:password@/dbname")
	if err != nil {
		panic(err.Error())
	}

	DB = db
}

main.go

package main

import (
	"fmt"
	"net/http"

	"github.com/techinscribed/repository-db/controllers"
	"github.com/techinscribed/repository-db/repositories"
	"github.com/techinscribed/repository-db/sqldb"
)

func main() {
	db := sqldb.ConnectDB()

	// Create repos
	userRepo := repositories.NewUserRepo(db)

	h := controllers.NewBaseHandler(userRepo)

	http.HandleFunc("/", h.HelloWorld)

	s := &http.Server{
		Addr: fmt.Sprintf("%s:%s", "localhost", "5000"),
	}

	s.ListenAndServe()

}

repo.go

package repositories

import (
	"database/sql"

	"github.com/techinscribed/repository-db/models"
)

// UserRepo implements models.UserRepository
type UserRepo struct {
	db *sql.DB
}

// NewUserRepo ..
func NewUserRepo(db *sql.DB) *UserRepo {
	return &UserRepo{
		db: db,
	}
}

// FindByID ..
func (r *UserRepo) FindByID(ID int) (*models.User, error) {
	return &models.User{}, nil
}

// Save ..
func (r *UserRepo) Save(user *models.User) error {
	return nil
}

struct_db.go

package sqldb

import "database/sql"

// ConnectDB opens a connection to the database
func ConnectDB() *sql.DB {
	db, err := sql.Open("mysql", "username:password@/dbname")
	if err != nil {
		panic(err.Error())
	}

	return db
}

use_global_db.go

package controllers

import (
	"fmt"
	"net/http"

	"github.com/techinscribed/global-db/sqldb"
)

// HelloWorld returns Hello, World
func HelloWorld(w http.ResponseWriter, r *http.Request) {
	if err := sqldb.DB.Ping(); err != nil {
		fmt.Println("DB Error")
	}
	
	w.Write([]byte("Hello, World"))
}

use_struct_db.go

package controllers

import (
	"database/sql"
	"fmt"
	"net/http"
)

// BaseHandler will hold everything that controller needs
type BaseHandler struct {
	db *sql.DB
}

// NewBaseHandler returns a new BaseHandler
func NewBaseHandler(db *sql.DB) *BaseHandler {
	return &BaseHandler{
		db: db,
	}
}

// HelloWorld returns Hello, World
func (h *BaseHandler) HelloWorld(w http.ResponseWriter, r *http.Request) {
	if err := h.db.Ping(); err != nil {
		fmt.Println("DB Error")
	}

	w.Write([]byte("Hello, World"))
}

use_struct_db_main.go

package main

import (
	"fmt"
	"net/http"

	"github.com/techinscribed/struct-db/controllers"
	"github.com/techinscribed/struct-db/sqldb"
)

func main() {
	db := sqldb.ConnectDB()

	h := controllers.NewBaseHandler(db)

	http.HandleFunc("/", h.HelloWorld)

	s := &http.Server{
		Addr: fmt.Sprintf("%s:%s", "localhost", "5000"),
	}

	s.ListenAndServe()

}

user.go

package models

// User ..
type User struct {
	Name string
}

// UserRepository ..
type UserRepository interface {
	FindByID(ID int) (*User, error)
	Save(user *User) error
}