Add Exists and ExistsMulti convenience methods

service/datastore/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 (
         "golang.org/x/net/context"
 )
 
@@ skipping 100 matching lines @@
 
         // GetAll retrieves all of the Query results into dst.
         //
         // dst must be one of:
         //   - *[]S or *[]*S where S is a struct
         //   - *[]P or *[]*P where *P is a concrete type implementing
         //     PropertyLoadSaver
         //   - *[]*Key implies a keys-only query.
         GetAll(q *Query, dst interface{}) error
 
+        // Does a Get for this key and returns true iff it exists. Will only return
+        // an error if it's not ErrNoSuchEntity. This is slightly more efficient
+        // than using Get directly, because it uses the underlying RawInterface to
+        // avoid some reflection and copies.
+        Exists(k *Key) (bool, error)
+
+        // Does a GetMulti for thes keys and returns true iff they exist. Will only
+        // return an error if it's not ErrNoSuchEntity. This is slightly more efficient
+        // than using Get directly, because it uses the underlying RawInterface to
+        // avoid some reflection and copies.
+        ExistsMulti(k []*Key) ([]bool, error)
+
         // Get retrieves a single object from the datastore
         //
         // dst must be one of:
         //   - *S where S is a struct
         //   - *P where *P is a concrete type implementing PropertyLoadSaver
         Get(dst interface{}) error
 
         // Put inserts a single object into the datastore
         //
         // src must be one of:
@@ skipping 34 matching lines @@
 
         // Testable returns the Testable interface for the implementation, or nil if
         // there is none.
         Testable() Testable
 
         // Raw returns the underlying RawInterface. The Interface and RawInterface may
         // be used interchangably; there's no danger of interleaving access to the
         // datastore via the two.
         Raw() RawInterface
 }