pass the mongodb bson.Objectid from JavaScript(fronend) to Go(backend)

Question

I want to update MongoDB object attribute value by checking object id. that is type is bson.Objectid. I am using mgo.v2 MongoDB Golang driver. But in that case I send the PUT request to the update API. I send the object id HEX value as string to the Golang API. But there is error happening in my Golang side when decoding HEX value into bson.Object type variable.
How do I do this properly.

---

Frontend :

HEXVALUE = "57f54ef4d6e0ac55f6c7ff24"

var widget = {id: HEXVALUE, position: 2, type: 2, class: "normal"};

     $.ajax({
            url: 'api/widget',
            type: 'PUT',
            contentType: "application/json",
            data: JSON.stringify(widget),
            success: function (data) {
                console.log(data);
            },
            error: function (e) {
                console.log(e);
            }
     });

Go side (Server side):

type Widget struct {
    Id       bson.ObjectId `json:"id" bson:"_id"`
    Position int           `json:"position" bson:"position"`
    Type     int           `json:"type" bson:"type"`
    Class    string        `json:"class" bson:"class"`
}


func UpdateWidget(w http.ResponseWriter, r *http.Request) (error) {
    decoder := json.NewDecoder(r.Body)
    var widget models.DashboardWidget
    err := decoder.Decode(&widget)
    if err != nil {
        log.Error("There is error happening decoding widget: %v", err);
        return err;
    }
 reurn nil
};

Output

log error : There is error happening decoding widget

How to decode hex value into bson.ObjectId type.

Answer 1

1-Decode hex value into bson.ObjectId type using:

bson.ObjectIdHex("57f54ef4d6e0ac55f6c7ff24")

2- To update MongoDB object attribute value by checking object id, you may use

c.Update(bson.M{"_id": widget.Id}, widget)

Here is the working code:

package main

import (
    "encoding/json"
    "fmt"
    "log"
    "net/http"
    "strings"

    "gopkg.in/mgo.v2"
    "gopkg.in/mgo.v2/bson"
)

func main() {
    session, err := mgo.Dial("localhost")
    if err != nil {
        panic(err)
    }
    defer session.Close()
    session.SetMode(mgo.Monotonic, true) // Optional. Switch the session to a monotonic behavior.
    c := session.DB("test").C("Widget")
    c.DropCollection()
    err = c.Insert(
        &Widget{bson.NewObjectId(), 1, 2, "c1"},
        &Widget{bson.NewObjectId(), 20, 2, "normal"},
        &Widget{bson.ObjectIdHex("57f54ef4d6e0ac55f6c7ff24"), 2, 2, "normal"})
    if err != nil {
        log.Fatal(err)
    }

    result := []Widget{}
    err = c.Find(bson.M{}).All(&result)
    if err != nil {
        log.Fatal(err)
    }
    fmt.Println(result)

    s := `{"id":"57f54ef4d6e0ac55f6c7ff24","position":2,"type":2,"class":"normal"}`
    decoder := json.NewDecoder(strings.NewReader(s))
    var widget Widget
    err = decoder.Decode(&widget)
    if err != nil {
        panic(err)
    }
    fmt.Println(widget)

    c.Update(bson.M{"_id": widget.Id}, widget)

    result2 := []Widget{}
    err = c.Find(bson.M{}).All(&result2)
    if err != nil {
        log.Fatal(err)
    }
    fmt.Println(result2)

    //http.HandleFunc("/", UpdateWidget)
    //http.ListenAndServe(":80", nil)

}
func UpdateWidget(w http.ResponseWriter, r *http.Request) {
    decoder := json.NewDecoder(r.Body)
    var widget Widget //models.DashboardWidget
    err := decoder.Decode(&widget)
    if err != nil {
        log.Fatal(err)
    }
}

type Widget struct {
    Id       bson.ObjectId `json:"id" bson:"_id"`
    Position int           `json:"position" bson:"position"`
    Type     int           `json:"type" bson:"type"`
    Class    string        `json:"class" bson:"class"`
}

output:

[{ObjectIdHex("57f62973c3176903402adb5e") 1 2 c1} {ObjectIdHex("57f62973c3176903402adb5f") 20 2 normal} {ObjectIdHex("57f54ef4d6e0ac55f6c7ff24") 2 2 normal}]
{ObjectIdHex("57f54ef4d6e0ac55f6c7ff24") 2 2 normal}
[{ObjectIdHex("57f62973c3176903402adb5e") 1 2 c1} {ObjectIdHex("57f62973c3176903402adb5f") 20 2 normal} {ObjectIdHex("57f54ef4d6e0ac55f6c7ff24") 2 2 normal}]

---

3- Your Code has some typos:

log error : There is error happening decoding widget

This error belongs to

err := decoder.Decode(&widget)

Change it to this:

err := decoder.Decode(&widget)
if err != nil {
    log.Fatal(err)
}

to see exact error.

---

Change

var widget models.DashboardWidget

to

var widget Widget

Like this:

func UpdateWidget(w http.ResponseWriter, r *http.Request) {
    decoder := json.NewDecoder(r.Body)
    var widget Widget //models.DashboardWidget
    err := decoder.Decode(&widget)
    if err != nil {
        log.Fatal(err)
    }
}

---

and

JSON.stringify(widget)

generates:

`{"id":"57f54ef4d6e0ac55f6c7ff24","position":2,"type":2,"class":"normal"}`

This works fine:

package main

import (
    "encoding/json"
    "fmt"
    "strings"

    "gopkg.in/mgo.v2/bson"
)

func main() {
    s := `{"id":"57f54ef4d6e0ac55f6c7ff24","position":2,"type":2,"class":"normal"}`
    decoder := json.NewDecoder(strings.NewReader(s))
    var widget Widget
    err := decoder.Decode(&widget)
    if err != nil {
        panic(err)
    }
    fmt.Println(widget)
}

type Widget struct {
    Id       bson.ObjectId `json:"id" bson:"_id"`
    Position int           `json:"position" bson:"position"`
    Type     int           `json:"type" bson:"type"`
    Class    string        `json:"class" bson:"class"`
}

output:

{ObjectIdHex("57f54ef4d6e0ac55f6c7ff24") 2 2 normal}