golang如何将这两个功能结合在一起？

Question

I want to learn to write clean code in golang, my problem is: I have two function and I need to combined to become only one, this is my actual code:

func db_execute(sql_cmd string) bool {

    db, err := sql.Open("mysql", mysql_login)
    if err != nil {
        log.Fatal(err)
    }
    defer db.Close()

    err = db.Ping()
    if err != nil {
        log.Fatal(err)
    }

    stmt, err := db.Prepare(sql_cmd)
    if err != nil {
        fmt.Print(err.Error())
    }
    _, err = stmt.Exec()

    if err != nil {
        fmt.Print(err.Error())
        return false
    }

    return true
}

func db_tabela_select(cod_cliente string) (id string, cod1 string, cod2 string, cod3 string) {

    db, err := sql.Open("mysql", mysql_login)
    if err != nil {
        log.Fatal(err)
    }
    defer db.Close()

    err = db.Ping()
    if err != nil {
        log.Fatal(err)
    }

    err = db.QueryRow("select id, cod1, cod2, cod3 from db_tabela WHERE `cliente`=? LIMIT 1;", cod_cliente).Scan(
                        &id, &cod1, &cod2, &cod3)

    switch {
        case err == sql.ErrNoRows:
                log.Printf("No codice cliente with that ID.")
        case err != nil:
                log.Printf("database select problems")
        default:
                fmt.Printf("Client code is %s %s %s
", cod1, cod2, cod3)
    }

    return id, cod1, cod2, cod3
}

How can I combine these 2 function in one? These functions have different input and different output.

Answer 1

You shouldn't "combine" those functions. What's common in them, move them "out", e.g. to a 3rd function which can be called by these 2.

Also, connecting to a DB should not be a "local" operation, it should only be done once, e.g. in a package init() function.

Moreover, functions that may fail (db operations are typical examples of these) should return an error, so it can be inspected and dealt with at the caller.

This is a simpler, more robust and more idiomatic solution to your example:

var db *sql.DB

func init() {
    var err error
    db, err = sql.Open("mysql", "db_url_string")
    if err != nil {
        log.Fatal(err)
    }

    if err = db.Ping(); err != nil {
        log.Fatal(err)
    }
}

func dbExecute(sql_cmd string) error {
    stmt, err := db.Prepare(sql_cmd)
    if err != nil {
        return err
    }
    _, err = stmt.Exec()
    return err
}

func dbTabelaSelect(cod_cliente string) (id, cod1, cod2, cod3 string, err error) {
    query := "select id, cod1, cod2, cod3 from db_tabela WHERE 'cliente'=? LIMIT 1"
    err = db.QueryRow(query, cod_cliente).Scan(&id, &cod1, &cod2, &cod3)
    return
}

Example using these functions:

func main() {
    defer db.Close() // Graceful shutdown

    if err := dbExecute("some_SQL"); err != nil {
        fmt.Print("SQL execution failed: %v", err)
    }

    id, cod1, cod2, cod3, err := dbTabelaSelect("someID")
    switch {
    case err == sql.ErrNoRows:
        log.Printf("No codice cliente with that ID.")
    case err != nil:
        log.Printf("database select problems")
    default:
        fmt.Printf("Client code is %s %s %s %s
", id, cod1, cod2, cod3)
    }
}