如何在GO的全局范围内存储和获取指针引用

Question

I have got the follow code:

package main


func main() {
    // create  a pointer referece of session of Mongo DB
session := mongoDB.CreateSession()

    // Question 1 : How to store a pointer reference in a global scope and using anywhere of the code  

defer session.Close()

    // Note I suppose that the code call to handler methods that call to the Process in the package controller(the last one code)

}

Code of creating a session of MongoDB

package mongoDB


func CreateSession() *mgo.Session {
session, err := mgo.Dial("192.168.0.108:27017/databasename")
if err != nil {
    panic(err)
}
session.SetMode(mgo.Monotonic, true)
return session
}

Place where I want to use the pointer reference that was store in the main

package controller


func Process()  {

    // Question 2 : How can a get the pointer reference store in Question 1 if is posible
collection := mongoDB.CreateCollection(session, "namedatabase", "colectionData")
mongoDB.InsertData(collection, "Ale", "45646565")

}

The idea is to avoid passing by reference session(my pointer reference in the main function) in every one of the functions created for all the project.

Answer 1

You can't have your controller package import main. That is not a good idea (and I am quite sure it is not even possible). But that doesn't mean you can't have a global session variable in the controller.

You can try this:

package main

import (
    "controller"
    "mongoDB"
)

func main() {
    // create  a pointer referece of session of Mongo DB
    session := mongoDB.CreateSession()
    defer session.Close()

    controller.SetDBSession(session) // Or controller.Init or whatever you like

    controller.Process()
}

And then in the controller package you have:

package controller

import "mongoDB"

// Global session var for the package
var session mongoDB.Session

// SetDBSession sets the mongoDB session to be used by the controller package.
// This function must be called before calling Process()
func SetDBSession(s mongoDB.Session) {
    session = s
}

func Process() {
    collection := mongoDB.CreateCollection(session, "namedatabase", "colectionData")
    mongoDB.InsertData(collection, "Ale", "45646565")
}

Using this solution, you will only have to pass the session to the controller package once, letting main take care of the creating and closing of the session.