Recommended way to make a client - go

Question

Let's assume that I want to make a client, for example, MySQL client (but my question is generic and not just for MySQL client, any client), this is a sample code
func main() {
db, err := sql.Open("mysql", "root:<yourMySQLdatabasepassword>#tcp(127.0.0.1:3306)/test")
if err != nil {
panic(err.Error())
}
defer db.Close()
}
I want to move it into a function so I don't have to initialize it all over the place and here my question begins I can do it in various ways and I want to know which one is the recommended way
Here is functional way
func client() (client *sql.DB, err error) {
client, err = sql.Open("mysql", "root:<yourMySQLdatabasepassword>#tcp(127.0.0.1:3306)/test")
if err != nil {
panic(err.Error())
}
return
}
Global variable way
var client, err = sql.Open("mysql", "root:<yourMySQLdatabasepassword>#tcp(127.0.0.1:3306)/test")
init func way
var Client *sql.DB
func init() {
Client, err := sql.Open("mysql", "root:root#tcp(localhost:3306)/otp")
if err != nil {
panic(err.Error())
}
}
and finally struct way
type MSQL struct {
// Fields...
}
func (m *MSQL) Client() *sql.DB {
client, err := sql.Open("mysql", "root:<yourMySQLdatabasepassword>#tcp(127.0.0.1:3306)/test")
if err != nil {
panic(err.Error())
}
return client
}
// NewMysql().where(...)
I'm really confused here to select which one to follow

Answer 1

Exposing a public variable var Client *sql.DB is error prone as I can do <package>.Client = null from anywhere.
struct way is the way to go, As you can work with multiple connection each to a specific database at any time.
You can also use New() to pass in a config object or other props to customise other db props. like Max Connection.
package database;
type Db struct{
*db sql.DB
}
func New(driver, connection string) *Db {
db, err := sql.Open(driver, connection)
if err != nil {
panic(err)
}
if err = db.Ping(); err != nil {
panic(err)
}
/* configure details
db.SetConnMaxLifetime(conLifeTime)
db.SetMaxOpenConns(maxOpenConns)
db.SetMaxIdleConns(maxIdleConns)
*/
return &Db{db}
}
func (d *Db) Close() error {
return d.db.Close();
}
Its generic, you can pass any driver & connection string for creating a connection to any database.
connection database.New("mysql", "root:<yourMySQLdatabasepassword>#tcp(127.0.0.1:3306)/test")
usage database.Db.Where(...)
close connection database.Db.Close()