Add missing Count api

impl/memory/datastore.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 memory
 
 import (
         "errors"
         "fmt"
 
@@ skipping 50 matching lines @@
 
 func (d *dsImpl) DecodeCursor(s string) (ds.Cursor, error) {
         return newCursor(s)
 }
 
 func (d *dsImpl) Run(fq *ds.FinalizedQuery, cb ds.RawRunCB) error {
         idx, head := d.data.getQuerySnaps(!fq.EventuallyConsistent())
         return executeQuery(fq, d.ns, false, idx, head, cb)
 }
 
+func (d *dsImpl) Count(fq *ds.FinalizedQuery) (ret int64, err error) {
+        idx, head := d.data.getQuerySnaps(!fq.EventuallyConsistent())
+        return countQuery(fq, d.ns, false, idx, head)
+}
+
 func (d *dsImpl) AddIndexes(idxs ...*ds.IndexDefinition) {
         if len(idxs) == 0 {
                 return
         }
 
         for _, i := range idxs {
                 if !i.Compound() {
                         panic(fmt.Errorf("Attempted to add non-compound index: %s", i))
                 }
         }
@@ skipping 57 matching lines @@
 }
 
 func (d *txnDsImpl) DecodeCursor(s string) (ds.Cursor, error) {
         return newCursor(s)
 }
 
 func (d *txnDsImpl) Run(q *ds.FinalizedQuery, cb ds.RawRunCB) error {
         return executeQuery(q, d.ns, true, d.data.snap, d.data.snap, cb)
 }
 
+func (d *txnDsImpl) Count(fq *ds.FinalizedQuery) (ret int64, err error) {
+        return countQuery(fq, d.ns, true, d.data.snap, d.data.snap)
+}
+
 func (*txnDsImpl) RunInTransaction(func(c context.Context) error, *ds.TransactionOptions) error {
         return errors.New("datastore: nested transactions are not supported")
 }
 
 func (*txnDsImpl) Testable() ds.Testable {
         return nil
 }