Make a Datastore key's namespace available to the app.

Change-Id: Icaad90e0958a516af684a522749df2299c1ed585

datastore/key.go

@@ -56,6 +56,11 @@ func (k *Key) AppID() string {
 	return k.appID
 }
 
+// Namespace returns the key's namespace.
+func (k *Key) Namespace() string {
+	return k.namespace
+}
+
 // Incomplete returns whether the key does not refer to a stored entity.
 // In particular, whether the key has a zero StringID and a zero IntID.
 func (k *Key) Incomplete() bool {

datastore/key_test.go

@@ -200,3 +200,15 @@ func TestIncompleteKeyWithParent(t *testing.T) {
 		t.Errorf("robert is invalid: %v", robert)
 	}
 }
+
+func TestNamespace(t *testing.T) {
+	key := &Key{
+		kind:      "Person",
+		intID:     1,
+		appID:     "s~some-app",
+		namespace: "mynamespace",
+	}
+	if g, w := key.Namespace(), "mynamespace"; g != w {
+		t.Errorf("key.Namespace() = %q, want %q", g, w)
+	}
+}