How to set namespace in appengine using go lang? - google-app-engine

Question

I am able to insert the entities with default namespace but I need to achieve multitenancy. Below is the code i am using to insert the entities and get the entities,but I need to assign namespaces for each entity.So i have followed below link but i am unable to set namespace please help me to fix
https://cloud.google.com/appengine/docs/standard/go/multitenancy/multitenancy
I found that there are two packages
1."cloud.google.com/go/datastore" - By using this package i am able to insert the entities with out namespace
2."google.golang.org/appengine/datastore" - I found this package from multi tenancy link by google,
I got the clarity that I need to use this package to assign namespaces but I am getting errors while using this package, Please help me to fix this
package main
import (
"fmt"
"net/http"
"google.golang.org/appengine"
"google.golang.org/appengine/datastore"
)
type user struct {
UserName string
Password string
First string
Last string
}
func main() {
fmt.Println("hi")
http.HandleFunc("/", handle)
http.Handle("/favicon.ico", http.NotFoundHandler())
http.ListenAndServe(":8080", nil)
}
func handle(w http.ResponseWriter, r *http.Request) {
ctx := appengine.NewContext(r)
k := datastore.NewKey(ctx, "user", "stringID", 0, nil)
e := new(user)
if err := datastore.Get(ctx, k, e); err != nil {
http.Error(w, err.Error(), 500)
return
}
old := e.First
e.First = r.URL.Path
if _, err := datastore.Put(ctx, k, e); err != nil {
http.Error(w, err.Error(), 500)
return
}
w.Header().Set("Content-Type", "text/plain; charset=utf-8")
fmt.Fprintf(w, "old=%q\nnew=%q\n", old, e.First)
}
Error :
While running the code from local host I am getting below error
E:/GoWork/src/google.golang.org/appengine/internal/api.go:270 +0x186
google.golang.org/appengine.WithContext(0xd60000, 0xc04200c320, 0xc042174000, 0xd60000, 0xc04200c320)
E:/GoWork/src/google.golang.org/appengine/appengine.go:73 +0x46
google.golang.org/appengine.NewContext(0xc042174000, 0x987460, 0xc04216c034)
E:/GoWork/src/google.golang.org/appengine/appengine.go:66 +0x6e
main.handle(0x959da0, 0xc042180000, 0xc042174000)
E:/GoWork/src/simplystdatastore/main.go:27 +0x4a
net/http.HandlerFunc.ServeHTTP(0x7e49c8, 0x959da0, 0xc042180000, 0xc042174000)
c:/go/src/net/http/server.go:1942 +0x4b
net/http.(*ServeMux).ServeHTTP(0x987460, 0x959da0, 0xc042180000, 0xc042174000)
c:/go/src/net/http/server.go:2238 +0x137
net/http.serverHandler.ServeHTTP(0xc042075550, 0x959da0, 0xc042180000, 0xc042174000)
c:/go/src/net/http/server.go:2568 +0x99
net/http.(*conn).serve(0xc0421280a0, 0x95a3a0, 0xc04216e040)
c:/go/src/net/http/server.go:1825 +0x619
created by net/http.(*Server).Serve
c:/go/src/net/http/server.go:2668 +0x2d5