Add transaction (a list of deltas) as a primitive for applying sets of changes

... and Fix idomaticness

graph/quadwriter.go

@@ -72,6 +72,7 @@ type QuadWriter interface {
 	// Add a quad to the store.
 	AddQuad(quad.Quad) error
 
+	// TODO(barakmich): Deprecate in favor of transaction.
 	// Add a set of quads to the store, atomically if possible.
 	AddQuadSet([]quad.Quad) error
 
@@ -79,6 +80,9 @@ type QuadWriter interface {
 	// if it exists. Does nothing otherwise.
 	RemoveQuad(quad.Quad) error
 
+	// Apply a set of quad changes
+	ApplyTransaction(*Transaction) error
+
 	// Cleans up replication and closes the writing aspect of the database.
 	Close() error
 }

graph/transaction.go

@@ -0,0 +1,43 @@
+// Copyright 2015 The Cayley Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package graph
+
+import (
+	"github.com/google/cayley/quad"
+)
+
+type Transaction struct {
+	Deltas []Delta
+}
+
+func NewTransaction() *Transaction {
+	return &Transaction{make([]Delta, 0, 5)}
+}
+
+func (t *Transaction) AddQuad(q quad.Quad) {
+	t.Deltas = append(t.Deltas,
+		Delta{
+			Quad:   q,
+			Action: Add,
+		})
+}
+
+func (t *Transaction) RemoveQuad(q quad.Quad) {
+	t.Deltas = append(t.Deltas,
+		Delta{
+			Quad:   q,
+			Action: Delete,
+		})
+}