Add Exists and ExistsMulti convenience methods

service/datastore/datastore_test.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.
 
 // adapted from github.com/golang/appengine/datastore
 
 package datastore
 
 import (
         "fmt"
@@ skipping 72 matching lines @@
         return nil
 }
 
 func (f *fakeDatastore) GetMulti(keys []*Key, _meta MultiMetaGetter, cb GetMultiCB) error {
         if keys[0].Kind() == "FailAll" {
                 return errors.New("GetMulti fail all")
         }
         for i, k := range keys {
                 if k.Kind() == "Fail" {
                         cb(nil, errors.New("GetMulti fail"))
+                } else if k.Kind() == "DNE" {
+                        cb(nil, ErrNoSuchEntity)
                 } else {
                         cb(PropertyMap{"Value": {MkProperty(i + 1)}}, nil)
                 }
         }
         return nil
 }
 
 func (f *fakeDatastore) DeleteMulti(keys []*Key, cb DeleteMultiCB) error {
         if keys[0].Kind() == "FailAll" {
                 return errors.New("DeleteMulti fail all")
@@ skipping 188 matching lines @@
                         })
 
                         Convey("a pls with $id, $parent", func() {
                                 pls := GetPLS(&CommonStruct{ID: 1})
                                 So(ds.KeyForObj(pls).String(), ShouldEqual, `s~aid:ns:/CommonStruct,1`)
 
                                 So(pls.SetMeta("parent", k), ShouldBeNil)
                                 So(ds.KeyForObj(pls).String(), ShouldEqual, `s~aid:ns:/Hello,"world"/CommonStruct,1`)
                         })
 
+                        Convey("can see if things exist", func() {
+                                e, err := ds.Exists(k)
+                                So(err, ShouldBeNil)
+                                So(e, ShouldBeTrue)
+
+                                e, err = ds.Exists(ds.MakeKey("DNE", "nope"))
+                                So(err, ShouldBeNil)
+                                So(e, ShouldBeFalse)
+
+                                _, err = ds.Exists(ds.MakeKey("Fail", "boom"))
+                                So(err, ShouldErrLike, "GetMulti fail")
+                        })
+
                 })
 
                 Convey("bad", func() {
                         Convey("a propmap without $kind", func() {
                                 pm := PropertyMap{}
                                 So(pm.SetMeta("id", 100), ShouldBeNil)
                                 So(func() { ds.KeyForObj(pm) }, ShouldPanic)
                         })
                 })
         })
@@ skipping 562 matching lines @@
                                 So(ds.Run(q, func(k *Key, _ CursorCB) bool {
                                         So(k.IntID(), ShouldEqual, i+1)
                                         i++
                                         return true
                                 }), ShouldBeNil)
                         })
 
                 })
         })
 }