Add PopulateKey method to datastore.

service/datastore/datastore.go

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package datastore
 
 import (
         "fmt"
         "io"
         "io/ioutil"
@@ skipping 34 matching lines @@
 }
 
 func (d *datastoreImpl) NewKey(kind, stringID string, intID int64, parent *Key) *Key {
         return NewKey(d.aid, d.ns, kind, stringID, intID, parent)
 }
 
 func (d *datastoreImpl) NewKeyToks(toks []KeyTok) *Key {
         return NewKeyToks(d.aid, d.ns, toks)
 }
 
+// PopulateKey loads key into obj.
+//
+// obj is any object that Interface.Get is able to accept.
+//
+// This method will panic if obj is an invalid datastore model. If the key could
+// not be applied to the object, nothing will happen.
+func PopulateKey(obj interface{}, key *Key) {
+        pls := getMGS(obj)
+        if !pls.SetMeta("key", key) {
+                lst := key.LastTok()
+                if lst.StringID != "" {
+                        pls.SetMeta("id", lst.StringID)
+                } else {
+                        pls.SetMeta("id", lst.IntID)
+                }
+                pls.SetMeta("kind", lst.Kind)
+                pls.SetMeta("parent", key.Parent())
+        }
+}
+
 func runParseCallback(cbIface interface{}) (isKey, hasErr, hasCursorCB bool, mat multiArgType) {
         badSig := func() {
                 panic(fmt.Errorf(
                         "cb does not match the required callback signature: `%T` != `func(TYPE, [CursorCB]) [error]`",
                         cbIface))
         }
 
         if cbIface == nil {
                 badSig()
         }
@@ skipping 376 matching lines @@
                 currentDir = filepath.Dir(currentDir)
         }
 }
 
 func filterStop(err error) error {
         if err == Stop {
                 err = nil
         }
         return err
 }