Errors Getting list of polls from mongoDB with go-gin and mgo

Hi trying to build a web service with go-gin and mgo on the Go language, i have a database with mongoDB but each time i try to GET polls from the database I get errors from the folowing errors from the Go webserver.

    2:00:16 PM web.1 |  	gopanic: reflectcall(nil, unsafe.Pointer(d.fn), deferArgs(d), uint32(d.siz), uint32(d.siz))
2:00:16 PM web.1 |  /home/go/src/gopkg.in/gin-gonic/gin.v1/context.go:180 (0x4e1eb1)
2:00:16 PM web.1 |  	(*Context).MustGet: panic("Key \"" + key + "\" does not exist")
2:00:16 PM web.1 |  /home/go/src/smartpoll/main.go:139 (0x401655)
2:00:16 PM web.1 |  	allPolls: db := c.MustGet("db").(*mgo.Database)
2:00:16 PM web.1 |  /home/go/src/gopkg.in/gin-gonic/gin.v1/context.go:97 (0x4e187a)
2:00:16 PM web.1 |  	(*Context).Next: c.handlers[c.index](c)
2:00:16 PM web.1 |  /home/go/src/gopkg.in/gin-gonic/gin.v1/recovery.go:45 (0x4f165a)
2:00:16 PM web.1 |  	RecoveryWithWriter.func1: c.Next()
2:00:16 PM web.1 |  /home/go/src/gopkg.in/gin-gonic/gin.v1/context.go:97 (0x4e187a)
2:00:16 PM web.1 |  	(*Context).Next: c.handlers[c.index](c)
2:00:16 PM web.1 |  /home/go/src/gopkg.in/gin-gonic/gin.v1/logger.go:72 (0x4f074f)
2:00:16 PM web.1 |  	LoggerWithWriter.func1: c.Next()
2:00:16 PM web.1 |  /home/go/src/gopkg.in/gin-gonic/gin.v1/context.go:97 (0x4e187a)
2:00:16 PM web.1 |  	(*Context).Next: c.handlers[c.index](c)
2:00:16 PM web.1 |  /home/go/src/gopkg.in/gin-gonic/gin.v1/gin.go:284 (0x4e7c0e)
2:00:16 PM web.1 |  	(*Engine).handleHTTPRequest: context.Next()
2:00:16 PM web.1 |  /home/go/src/gopkg.in/gin-gonic/gin.v1/gin.go:265 (0x4e74f0)
2:00:16 PM web.1 |  	(*Engine).ServeHTTP: engine.handleHTTPRequest(c)
2:00:16 PM web.1 |  /home/kebe/golang/go/src/net/http/server.go:2202 (0x4b249d)
2:00:16 PM web.1 |  	serverHandler.ServeHTTP: handler.ServeHTTP(rw, req)
2:00:16 PM web.1 |  /home/kebe/golang/go/src/net/http/server.go:1579 (0x4aee07)
2:00:16 PM web.1 |  	(*conn).serve: serverHandler{c.server}.ServeHTTP(w, w.req)
2:00:16 PM web.1 |  /home/kebe/golang/go/src/runtime/asm_amd64.s:2086 (0x45a081)
2:00:16 PM web.1 |  	goexit: BYTE	$0x90	// NOP
2:00:16 PM web.1 |  
2:00:16 PM web.1 |  [GIN] 2017/06/20 - 14:00:16 | 500 |  753.521212ms | 127.0.0.1 |   GET     /polls

My Code is as follows

package main
import (
"fmt"
"log"
"net/http"  
"os"
"gopkg.in/gin-gonic/gin.v1"
"gopkg.in/mgo.v2"
)
type Poll struct {
ID        string `json:"id,omitempty"`
Firstname string `json:"firstname,omitempty"`
Lastname  string `json:"lastname,omitempty"`
Poll      string `json:"poll,omitempty"`
}
var (
// Session stores mongo session
Session *mgo.Session
// Mongo stores the mongodb connection string information
Mongo *mgo.DialInfo
)
const (
// MongoDBUrl is the default mongodb url that will be used to connect to the
// database.
MongoDBUrl = "mongodb://localhost:27017/smartpoll"
// CollectionPoll holds the name of the articles collection
CollectionPoll = "polls"
)
// Connect connects to mongodb
func Connect() {
uri := os.Getenv("MONGODB_URL")
if len(uri) == 0 {
uri = MongoDBUrl
}
mongo, err := mgo.ParseURL(uri)
s, err := mgo.Dial(uri)
if err != nil {
fmt.Printf("Can't connect to mongo, go error %v\n", err)
panic(err.Error())
}
s.SetSafe(&mgo.Safe{})
fmt.Println("Connected to", uri)
Session = s
Mongo = mongo
}
func init() {
Connect()
}
func main() {
port := os.Getenv("PORT")
if port == "" {
log.Fatal("$PORT must be set")
}
router := gin.Default()
router.GET("/", func (c *gin.Context) {
c.JSON(http.StatusOK, gin.H{"message": "OK"})
})
router.GET("/polls", allPolls)
router.Run(":" + port)
}
func allPolls(c *gin.Context) {
db := c.MustGet("db").(*mgo.Database)
polls := []Poll{}
poll := db.C(CollectionPoll).Find(&polls)
c.JSON(http.StatusOK, gin.H{
"_id": "ID",
"firstname": "Firstname",
"lastname": "Lastname",
"poll": poll,
})
}

My DB is as follows:

/* 0 */
{
"_id" : ObjectId("58d9cf1cdf353f3d2f5951b4"),
"id" : "1",
"firstname" : "Sam",
"lastname" : "Smith",
"poll" : "Who is the Richest Man in the World"
}

To get the database object (db) from the gin context (c) c.MustGet("db").(*mgo.Database) you have to first set it using a gin middleware function

func ConnectMiddleware(c *gin.Context) {
c.Set("db", Session.DB(Mongo.Database))
c.Next()
}

and then use this middleware through the following code

router := gin.Default()
router.Use(ConnectMiddleware)
router.GET("/", func(c *gin.Context) {
c.JSON(http.StatusOK, gin.H{"message": "OK"})
})
router.GET("/polls", allPolls)

You are using a outdated version of gin library other things are fine in your code

import the latest package form github.com/gin-gonic/gin

Use this to get the data from the database

func allPolls(c *gin.Context) {
db := c.MustGet("db").(*mgo.Database)
polls := []Poll{}
err := db.C(CollectionPoll).Find(nil).All(&polls)
if err != nil {
c.Error(err)
}
result := gin.H{"payload": polls}
c.Writer.Header().Set("Content-Type", "application/json")
c.JSON(200, result)
}

There is no variable named "db" in your request.

When you're executing c.MustGet("db") you're assure that there is a param with this name, but it isn't presented.

Gin code which panics

You need to pass "db" name in to your request.

Better solution: if it's not present return HTTP error 400 Bad request.