golang mongo defer sessions

Question

I am creating the mongodb connection from main method and defer that open connection.

func main(){
    session := db.CreateConnection(connectionStr)
    defer session.Close()
}

The issue is I need to pass this sesstion object to user handler struct and from that pass to db handler.

type UserController struct {
    DB DBOps
}

type DBOps struct {
    session *mgo.Session
}

Question: How can we directly create the session object and inside db handler file and defer that when application closes ?

db.go

type DBOps struct {
    session *mgo.Session
}

func (m *DBOps) Init(connectionstr string) error {
    session, err := mgo.Dial(connectionstr)

    // Check if connection error, is mongo running?
    if err != nil {
        panic(err)
    }
}

inside main function I can just call

func main(){
    db.Init(connectionstr);
}

but How to defer this session object on the main method ?

Related, see this answer [how MongoDB session should be handled / used](https://stackoverflow.com/questions/47179890/too-many-open-files-in-mgo-go-server/47180097#47180097). — icza, Jan 09 '18 at 09:40
OK thanks. understood. But the session created on init will be there even after close the main method. Thats my worry ? — R.Roshan, Jan 09 '18 at 09:53
If you return from the `main` function, your whole app will terminate and not wait for other non-`main` goroutines to complete. See: [What's wrong with this golang code?](https://stackoverflow.com/questions/28958192/whats-wrong-with-this-golang-code/28958240#28958240) — icza, Jan 09 '18 at 09:53

Himanshu · Answer 1 · 2018-02-18T12:03:21.800

you can create global variable for assigning the session object, return session object from a function. Use session object to fetch data and then defer the session after querying from mongo.

var (
    mgoSession     *mgo.Session
    databaseName = "myDB"
)

func getSession () *mgo.Session {
    if mgoSession == nil {
        var err error
        mgoSession, err = mgo.Dial("localhost")
        if err != nil {
             panic(err) // no, not really
        }
    }
    return mgoSession.Clone()
}

func withCollection(collection string, s func(*mgo.Collection) error)   
{    
    session := getSession()
    defer session.Close()
    c := session.DB(databaseName).C(collection)
    return s(c)
}

I have cloned session object and returned it to function used to query mongo and defer the session there. By above approach you can directly access session object inside handler.

golang mongo defer sessions

1 Answers1