Add 'user friendly' datastore API.

service/rawdatastore/errors.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 rawdatastore
-
-import (
-        "fmt"
-        "reflect"
-
-        "google.golang.org/appengine/datastore"
-)
-
-// These errors are returned by various rawdatastore.Interface methods.
-var (
-        ErrInvalidEntityType     = datastore.ErrInvalidEntityType
-        ErrInvalidKey            = datastore.ErrInvalidKey
-        ErrNoSuchEntity          = datastore.ErrNoSuchEntity
-        ErrConcurrentTransaction = datastore.ErrConcurrentTransaction
-        ErrQueryDone             = datastore.Done
-
-        // ErrMetaFieldUnset is returned from PropertyLoadSaver.{Get,Set}Meta
-        // implementations when the specified meta key isn't set on the struct at
-        // all.
-        ErrMetaFieldUnset = fmt.Errorf("gae: meta field unset")
-)
-
-// ErrFieldMismatch is returned when a field is to be loaded into a different
-// type than the one it was stored from, or when a field is missing or
-// unexported in the destination struct.
-// StructType is the type of the struct pointed to by the destination argument
-// passed to Get or to Iterator.Next.
-type ErrFieldMismatch struct {
-        StructType reflect.Type
-        FieldName  string
-        Reason     string
-}
-
-func (e *ErrFieldMismatch) Error() string {
-        return fmt.Sprintf("gae: cannot load field %q into a %q: %s",
-                e.FieldName, e.StructType, e.Reason)
-}