Mgo insert command not creating db or inserting document

Question

My goal is to implement this code. Except instead of using sql I want to use mongoDB. I think there is an issue with how I handle my sessions.

I'm trying to use mgo to insert some user data into MongoDB via a Rest API. Whenever I open the mongo shell and run the show dbs command, the poll DB is not displayed. I'm using Postman to test the Rest API. Any ideas what am I might be doing wrong in the insertion process? I tried creating the collection first in the mongo shell and then running the CreateUser function but I still didnt see the poll DB get created.

User

type User struct {
    Id bson.ObjectId `json:"id" bson:"_id,omitempty"`
    Username string `json:"username"`
    Password string  `json:"password"`
    Email string `json:"email"`
}

UserDAO

type UserDAO struct {
    session *mgo.Session
}

Creating a session

func GetMongoSession() *mgo.Session {
    if mgoSession == nil {
        var err error
        mgoSession, err = mgo.Dial("localhost")
        mgoSession.SetMode(mgo.Monotonic, true)

        if err != nil {
            log.Fatal("Failed to start the Mongo session.")
        }
    }
    return mgoSession.Clone()
}

I pass a User struct into the CreateUser function that I create using Postman:

{
    "username":"uname",
    "password":"pass",
    "email":"[email protected]"
}

Then I just respond with the same struct and receive this output:

{
    "id": "",
    "username": "uname",
    "password": "pass",
    "email": "[email protected]"
}

Creating a user

func (dao *UserDAO) CreateUser(u *User) (*User, error) {
    //return errors.New("Not implemented")

    // Get "users" collection

    dao.session = GetMongoSession()

    c := dao.session.DB("poll").C("user")

    defer dao.session.Close()

    //u.Id = bson.NewObjectId()
    err :=  c.Insert(u)

    if err != nil { 
        return nil, err
    }

    return u, nil
}

Http handler function

func (h *Handler) CreateUserReq(w http.ResponseWriter, r *http.Request) {

    // create new user using information from the Request object
    var user User
    decoder := json.NewDecoder(r.Body)

    if err := decoder.Decode(&user); err != nil {
        panic(err)
    }

    defer r.Body.Close()

    // Create new User
    u, err := h.UserService.CreateUser(&user)
    if err != nil {
        panic(err)
    }
    json.NewEncoder(w).Encode(*u)
}

Output of show dbs

> show dbs
admin   0.000GB
config  0.000GB
local   0.000GB

first of all your getting pointer to user struct so u need to pass the address to to u struct like this in &u in your function of insert — Himanshu
– Himanshu, Commented Feb 11, 2018 at 17:32
I'm passing in a pointer to a user, CreateUser(u *User), so isn't the u that gets passing into c.Insert(u) already the address of the object? — Sogun
– Sogun, Commented Feb 11, 2018 at 18:33

Saleem · Accepted Answer · 2018-02-11 19:12:42Z

2

Since, I don't have full context of your application so can't diagnose what exactly issue is with your code. But I came up with close example, which is working as expected.

Please see code below.

package main

import (
    "gopkg.in/mgo.v2"
    "log"
    "gopkg.in/mgo.v2/bson"
)

type User struct {
    Id       bson.ObjectId `json:"id" bson:"_id,omitempty"`
    Username string        `json:"username"`
    Password string        `json:"password"`
    Email    string        `json:"email"`
}

func GetMongoSession() *mgo.Session {

    mgoSession, err := mgo.Dial("localhost")
    mgoSession.SetMode(mgo.Monotonic, true)

    if err != nil {
        log.Fatal("Failed to start the Mongo session.")
    }

    return mgoSession.Clone()
}

func CreateUser(u *User) (*User, error) {

    session := GetMongoSession()

    c := session.DB("poll").C("user")
    defer session.Close()

    err := c.Insert(u)

    if err != nil {
        return nil, err
    }

    return u, nil
}

func main() {

    var user = User{
        Email:    "[email protected]",
        Password: "My-secret",
        Username: "YouGuess",
    }

    _, e := CreateUser(&user)
    if e != nil {
        panic(e)
    }

    log.Println("Done...")
}

once you execute it, you should see a document in MongoDB provided that you successfully establish connection with proper credentials.

I can see following document in my collection:

{
    "_id": ObjectId("5a80941de0a0f75123aeb435"),
    "username": "YouGuess",
    "password": "My-secret",
    "email": "[email protected]"
}

answered Feb 11, 2018 at 19:12

Saleem

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2 Comments

Sogun Over a year ago

Sorry about the vagueness, I was trying not to make the post too long which might make things more complicated. What I'm doing in my code is implementing the architecture found here: medium.com/@benbjohnson/standard-package-layout-7cdbc8391fc1. The difference in mine would be instead of using the sql driver, I would use mgo. In the postgres.go file, I would use session *mgo.Session instesad of DB *sql.DB.

Sogun Over a year ago

This ended up working for me after removing the DB I had created through the mongo shell and rerunning my code.

Himanshu · Accepted Answer · 2018-02-11 19:33:27Z

0

Try below code and first of all I check is my user struct contains data coming from postman and then there is one error also when you are assigning the session *mgo.Session to non-pointer dao.session variable. So I have changed many a things and it is working fine creating both database with poll name and creating a user collection with new document also I have removed ObjectId from User struct. Check it out

package main

import (
    "encoding/json"
    "gopkg.in/mgo.v2"
    "log"
    // "gopkg.in/mgo.v2/bson"
)

var (
    mgoSession     *mgo.Session
)

type UserDAO struct{
    session   *mgo.Session
}

type User struct {
    Username string `json:"username"`
    Password string  `json:"password"`
    Email string `json:"email"`
}

func GetMongoSession() *mgo.Session {
    if mgoSession == nil {
        var err error
        mgoSession, err = mgo.Dial("localhost")
        mgoSession.SetMode(mgo.Monotonic, true)

        if err != nil {
            log.Fatal("Failed to start the Mongo session.")
        }
    }
    return mgoSession.Clone()
}

func (dao *UserDAO) CreateUser(u *User) (*User, error) {
    //return errors.New("Not implemented")

    // Get "users" collection

    session := GetMongoSession()
    // log.Println(session)

    c := session.DB("poll").C("user")

    defer session.Close()

    //u.Id = bson.NewObjectId()
    err :=  c.Insert(u)

    if err != nil { 
        return nil, err
    }

    return u, nil
}

func main(){
    // this data will come from postman in your case
    jsonStr := []byte(`{
            "username":"uname",
            "password":"pass",
            "email":"[email protected]"
        }
    `)

    var user User
    err  := json.Unmarshal(jsonStr, &user)
    if err != nil{
        log.Println(err)
    }

    var dao *UserDAO

    dao.CreateUser(&user)
}

My collection output is:-

{
    "_id" : ObjectId("5a80993f32fcc2489f995aaf"),
    "username" : "uname",
    "password" : "pass",
    "email" : "[email protected]"
}

you don't need to create a Object id for new document it will be created itself when inserting a new document. Also If you wants top just create a collection using golang and then insert data you can create it explicitly. Go through this function create collection

edited Feb 11, 2018 at 19:33

answered Feb 11, 2018 at 17:34

Himanshu

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3 Comments

Sogun Over a year ago

I figured an Object Id would be created on insertion but was not sure, thanks for clarifying. I created the "poll" db and the "user" collection. I then ran my Postman request to create the user and did a db.user.find() in the mongo shell. There was no output though so I dont think the insert worked.

Sogun Over a year ago

I updated the code in the original question to include my UserDAO struct. dao.session is of type *User so that should be ok. The link I posted is essentially what my code is trying to do.

Himanshu Over a year ago

I have tried yor code but it panics every time I assign session to your dao struct session variable in this line dao.session = GetMongoSession(). you can try above code it is working fine. I have tested it completely

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