Fix error message from KeyForObj when passing an invalid struct.

service/datastore/raw_interface.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"
 
         "golang.org/x/net/context"
@@ skipping 34 matching lines @@
 //   - err is an error associated with putting this entity.
 type PutMultiCB func(key *Key, err error)
 
 // DeleteMultiCB is the callback signature provided to RawInterface.DeleteMulti
 //
 //   - err is an error associated with deleting this entity.
 type DeleteMultiCB func(err error)
 
 type nullMetaGetterType struct{}
 
-func (nullMetaGetterType) GetMeta(string) (interface{}, error)                   { return nil, ErrMetaFieldUnset }
-func (nullMetaGetterType) GetMetaDefault(_ string, dflt interface{}) interface{} { return dflt }
+func (nullMetaGetterType) GetMeta(string) (interface{}, bool) { return nil, false }
 
 var nullMetaGetter MetaGetter = nullMetaGetterType{}
 
 // MultiMetaGetter is a carrier for metadata, used with RawInterface.GetMulti
 //
 // It's OK to default-construct this. GetMeta will just return
 // (nil, ErrMetaFieldUnset) for every index.
 type MultiMetaGetter []MetaGetter
 
 // NewMultiMetaGetter returns a new MultiMetaGetter object. data may be nil.
 func NewMultiMetaGetter(data []PropertyMap) MultiMetaGetter {
         if len(data) == 0 {
                 return nil
         }
         inner := make(MultiMetaGetter, len(data))
         for i, pm := range data {
                 inner[i] = pm
         }
         return inner
 }
 
 // GetMeta is like PropertyLoadSaver.GetMeta, but it also takes an index
 // indicating which slot you want metadata for. If idx isn't there, this
 // returns (nil, ErrMetaFieldUnset).
-func (m MultiMetaGetter) GetMeta(idx int, key string) (interface{}, error) {
+func (m MultiMetaGetter) GetMeta(idx int, key string) (interface{}, bool) {
         return m.GetSingle(idx).GetMeta(key)
 }
 
-// GetMetaDefault is like PropertyLoadSaver.GetMetaDefault, but it also takes an
-// index indicating which slot you want metadata for. If idx isn't there, this
-// returns dflt.
-func (m MultiMetaGetter) GetMetaDefault(idx int, key string, dflt interface{}) interface{} {
-        return m.GetSingle(idx).GetMetaDefault(key, dflt)
-}
-
 // GetSingle gets a single MetaGetter at the specified index.
 func (m MultiMetaGetter) GetSingle(idx int) MetaGetter {
         if idx >= len(m) || m[idx] == nil {
                 return nullMetaGetter
         }
         return m[idx]
 }
 
 // RawInterface implements the datastore functionality without any of the fancy
 // reflection stuff. This is so that Filters can avoid doing lots of redundant
@@ skipping 66 matching lines @@
         //   - len(keys) > 0
         //   - all keys are Valid, !Incomplete, and in the current namespace
         //   - none keys of the keys are 'special' (use a kind prefixed with '__')
         //   - cb is not nil
         DeleteMulti(keys []*Key, cb DeleteMultiCB) error
 
         // Testable returns the Testable interface for the implementation, or nil if
         // there is none.
         Testable() Testable
 }