GAE/Go: Namespace not working

I am trying to store datastore record in namespace MyNameSpace with GAE/Go, but the code below not working.

import (
	"cloud.google.com/go/datastore"
	"github.com/gin-gonic/gin"
	"google.golang.org/appengine"
)

func Save(c *gin.Context, list []MyStruct) ([]MyStruct, error) {
	r := c.Request
	ctx := appengine.NewContext(r)
	ctx_with_namespace, err := appengine.Namespace(ctx, "MyNameSpace")
	if err != nil {
		return nil, err
	}

	client, err := datastore.NewClient(ctx_with_namespace, "MyProject")
	if err != nil {
		return nil, err
	}
	
	var keyList []*datastore.Key
	for _, v := range list {
		key := datastore.NameKey("MyStruct", v.ColA, nil)
		keyList = append(keyList, key)
	}
	
	_, err = client.PutMulti(ctx_with_namespace, keyList, list)
	
	return list,nil
}

This code creates records in the default namespace, not MyNameSpace.

Does cloud.google.com/go/datastore ignores namespace setting?

I found this document

> November 8, 2016
>
> Breaking changes to datastore: contexts no longer hold namespaces;
> instead you must set a key's namespace explicitly. Also, key functions
> have been changed and renamed.
>
> The WithNamespace function has been removed. To specify a namespace in
> a Query, use the Query.Namespace method:
>
> q := datastore.NewQuery("Kind").Namespace("ns")
>
> All the fields of Key are exported. That means you can construct any Key with a struct literal:
>
> k := &Key{Kind: "Kind", ID: 37, Namespace: "ns"}

I realized I should explicitly set namespace, but it is very inconvenient. I migrated to use google.golang.org/appengine/datastore