Better attempt at an appengine wrapper.

go/src/infra/gae/libs/meta/eg.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.
 
-// +build appengine
-
 package meta
 
 import (
+        "golang.org/x/net/context"

[M-A Ruel, 2015/05/25 17:14:50]

Why golang.org and github.com not be grouped together. Personally, I only use 2
groups: stdlib and everything else. That's what goimports generates by default
anyway.

[iannucci, 2015/05/26 18:25:05]

Ok, I was unsure of this. I was trying to do something like what we do for
python:

  stdlib

  [appengine imports because they're pseudo-stdlib]

  external (not owned by us) libs

  internal (owned by us)

I was considering golang.org/x to be 'stdlib' for all practical purposes.

Do we want to just do 2 groups, pure-stdlib (like: real stdlib, not
stdlib+appengine), and then everything else?

[M-A Ruel, 2015/05/27 00:27:10]

I prefer the result of the following:

pack everything in a single block
run goimports -w .

whatever is generated by that becomes the golden standard.

+
         "appengine/datastore"
 
         "github.com/luci/luci-go/common/errors"
 
-        "infra/gae/libs/context"
+        "infra/gae/libs/wrapper"
 )
 
 var mark = errors.MakeMarkFn("eg")
 
 // EntityGroupMeta is the model corresponding to the __entity_group__ model in
 // appengine. You shouldn't need to use this struct directly, but instead should
 // use GetEntityGroupVersion.
 type EntityGroupMeta struct {
         _kind string `datastore:"-" goon:"kind,__entity_group__"`
 
         ID     int64          `datastore:"-" goon:"id"`
         Parent *datastore.Key `datastore:"-" goon:"parent"`
 
         Version int64 `datastore:"__version__"`
 }
 
 // GetEntityGroupVersion returns the entity group version for the entity group
 // containing root. If the entity group doesn't exist, this function will return
 // zero and a nil error.
-func GetEntityGroupVersion(c context.SingleReadWriter, root *datastore.Key) (int64, error) {
+func GetEntityGroupVersion(c context.Context, root *datastore.Key) (int64, error) {
+        ds := wrapper.GetDS(c)
         for root.Parent() != nil {
                 root = root.Parent()
         }
         egm := &EntityGroupMeta{ID: 1, Parent: root}
-        err := c.Get(egm)
+        err := ds.Get(egm)
         if err != datastore.ErrNoSuchEntity {
                 err = mark(err)
         } else {
                 // this is OK for callers. The version of the entity group is effectively 0
                 // in this case.
                 err = nil
         }
         return egm.Version, err
 }