Il giorno venerdì 5 gennaio 2018 16:57:04 UTC+1, Ayan George ha scritto:
>
>
>
> On 01/05/2018 10:16 AM, Manlio Perillo wrote:
> > Recently I have developed a few web applications in Go, using a
> > PostgreSQL database, but I have yet understand the best way to use
> > the database/sql package.
> >
>
> I don't know how you're serving web pages but I typically use net/http.
> This also means that I typically build an http.Server. This requires
> that I create a type that conforms to the http.Handler interface.
>
Yes, I use the standard net/http interface, without frameworks (but I use a
simple toolkit written by me).
>
> You can use this type to pass around all of the data you need, including
> sql.DB instances, log.Logger, etc.
>
> So here's the skeleton of what I normally do. I haven't tested this --
> this is just to get the point across. Finally, this may be completely
> off base. I'm open to any criticisms etc. anyone may have.
>
> package main
>
> import (
> "database/sql"
> _ "github.com/lib/pq"
> "log"
> "net/http"
> "time"
> )
>
> type app struct {
> db *sql.DB
> }
>
> func (a *app) ServeHTTP(w http.ResponseWriter, r *http.Request) {
> // here we can use all of the fields of our app struct -- including
> the db!
>
> row := db.QueryRow("select current_timestamp;")
>
> var time string
> err := row.Scan(&time)
>
> if err != nil {
> // handle the error. maybe log it? i typically
> // create a log.Logger instance in my app and use it
> // at times like these.
> return
> }
>
> w.Write([]byte("<h1>hello, world!</h1>"))
> }
>
> func main() {
> db, err := sql.Open("postgres", "...")
>
> if err != nil {
> log.Fatal(err)
> }
>
> if err := db.Ping(); err != nil {
> log.Fatal(err)
> }
>
> myapp := app{
> db: db,
> }
>
> srv := http.Server{
> Addr: ":8080",
> ReadTimeout: 1 * time.Second,
> WriteTimeout: 1 * time.Second,
> Handler: &myapp,
> }
>
> log.Fatal(srv.ListenAndServe())
> }
>
Thanks, this is a very good solution.
Currently I'm using something different, however.
I have a package that exports the same API as database/sql, but as free
functions using a global *DB configured when loading a configuration file.
However the question is the same, and it is how and what to pass to
functions that need a connection to the database.
Passing *DB is no good; take as an example a "generic" package having
type Table struct {
A int
B string
}
func SaveTable(t *Table, db *DB) ...
or
func SaveTable(t *Table, tx *Tx) ...
The function does not need to know if it is inside a transaction; it is the
responsibility of the caller.
However consider a package with
type Table struct {
A int
B string
}
type OtherTable struct {
Table
C float64
B bool
}
Now the function SaveOtherTable may want to use a transaction to save Table
and OtherTable separately.
You surely can not pass a *Tx, since it does not support nested
transactions.
Thanks
Manlio Perillo
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