Add Key.HasAncestor()

service/datastore/key.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 (
         "bytes"
         "encoding/base64"
         "encoding/json"
@@ skipping 341 matching lines @@
                 a, b := k.toks[i], other.toks[i]
                 if a.Less(b) {
                         return true
                 } else if b.Less(a) {
                         return false
                 }
         }
         return len(k.toks) < len(other.toks)
 }
 
+// HasAncestor returns true iff other is an ancestor of k (or if other == k).
+func (k *Key) HasAncestor(other *Key) bool {
+        if k.appID != other.appID || k.namespace != other.namespace {
+                return false
+        }
+        if len(k.toks) < len(other.toks) {
+                return false
+        }
+        for i, tok := range other.toks {
+                if tok != k.toks[i] {
+                        return false
+                }
+        }
+        return true
+}
+
 // GQL returns a correctly formatted Cloud Datastore GQL key literal.
 //
 // The flavor of GQL that this emits is defined here:
 //   https://cloud.google.com/datastore/docs/apis/gql/gql_reference
 func (k *Key) GQL() string {
         ret := &bytes.Buffer{}
         fmt.Fprintf(ret, "KEY(DATASET(%s)", gqlQuoteString(k.appID))
         if k.namespace != "" {
                 fmt.Fprintf(ret, ", NAMESPACE(%s)", gqlQuoteString(k.namespace))
         }
@@ skipping 49 matching lines @@
         for _, t := range k.toks {
                 ret += int64(len(t.Kind))
                 if t.StringID != "" {
                         ret += int64(len(t.StringID))
                 } else {
                         ret += 8
                 }
         }
         return ret
 }