Best Practise opening DB

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.