Best Practise opening DB - go

Question

Note: I am not sure if this is the most accurate title for this post, if not, please advise on a better one.
Currently I am creating a server where I have a couple of handlers (using goji). After receiving a request, I want to interact with a MongoDB database I have (using mgo). My question is:
I am assuming doing this kind of stuff every time I am handling a request is expensive:
uri := os.Getenv("MONGOHQ_URL")
if uri == "" {
panic("no DB connection string provided")
}
session, err := mgo.Dial(uri)
So, would it be better for me to have a global var that I can access from inside the handlers? So I would go with something like this:
var session *mgo.Session
func main() {
session = setupDB()
defer session.Close()
goji.Get("/user", getUser)
goji.Serve()
}
func getUser(c web.C, w http.ResponseWriter, r *http.Request) {
// Use the session var here
}
My question is related to what would be the best practise here? Opening the DB every time a request comes in, or keep it open for the entire duration of the application.

Answer 1

What about wraping your handler in a Controller struct like this: (http://play.golang.org/p/NK6GO_lqgk)
package main
import (
"fmt"
"log"
"net/http"
"os"
"github.com/zenazn/goji"
"github.com/zenazn/goji/web"
)
type Controller struct {
session *Session
}
func NewController() (*Controller, error) {
if uri := os.Getenv("MONGOHQ_URL"); uri == "" {
return nil, fmt.Errorf("no DB connection string provided")
}
session, err := mgo.Dial(uri)
if err != nil {
return nil, err
}
return &Controller{
session: session,
}, nil
}
func (c *Controller) getUser(c web.C, w http.ResponseWriter, r *http.Request) {
// Use the session var here
}
func main() {
ctl, err := NewController()
if err != nil {
log.Fatal(err)
}
defer ctl.session.Close()
goji.Get("/user", ctl.getUser)
goji.Serve()
}
This way, you can embed your session in your handler and add any other data that you might need.