Refactoring of Delta.IDs & horizon functionality with a PrimaryKey type, needed for implementing UUID based primary keys for backends such as the appengine datastore \n Tests: at top level and if available per backend, if not then just visual

keys/sequentialkey.go

@@ -0,0 +1,51 @@
+// Copyright 2014 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 keys
+
+import (
+	"github.com/google/cayley/graph"
+	"strconv"
+	"sync"
+)
+
+type Sequential struct {
+	nextID int64
+	mut    sync.Mutex
+}
+
+func NewSequentialKey(horizon int64) graph.PrimaryKey {
+	if horizon <= 0 {
+		horizon = 1
+	}
+	return &Sequential{nextID: horizon}
+}
+
+func (s *Sequential) Next() graph.PrimaryKey {
+	s.mut.Lock()
+	defer s.mut.Unlock()
+	s.nextID++
+	if s.nextID <= 0 {
+		s.nextID = 1
+	}
+	return s
+}
+
+func (s *Sequential) Int() int64 {
+	return s.nextID
+}
+
+func (s *Sequential) String() string {
+	return strconv.FormatInt(s.nextID, 10)
+}