Add plumbing for bolt upgrades

graph/bolt/migrate.go

@@ -0,0 +1,84 @@
+// 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 bolt
+
+import (
+	"fmt"
+
+	"github.com/barakmich/glog"
+	"github.com/boltdb/bolt"
+	"github.com/google/cayley/graph"
+)
+
+const latestDataVersion = 1
+const nilDataVersion = 1
+
+type upgradeFunc func(*bolt.DB) error
+
+var migrateFunctions = []upgradeFunc{
+	nil,
+	upgrade1To2,
+}
+
+func upgradeBolt(path string, opts graph.Options) error {
+	db, err := bolt.Open(path, 0600, nil)
+	defer db.Close()
+	if err != nil {
+		glog.Errorln("Error, couldn't open! ", err)
+		return err
+	}
+	var version int64
+	err = db.View(func(tx *bolt.Tx) error {
+		version, err = getInt64ForMetaKey(tx, "version", nilDataVersion)
+		return err
+	})
+	if err != nil {
+		glog.Errorln("error:", err)
+		return err
+	}
+
+	if version == latestDataVersion {
+		fmt.Printf("Already at latest version: %d\n", latestDataVersion)
+		return nil
+	}
+
+	if version > latestDataVersion {
+		err := fmt.Errorf("Unknown data version: %d -- upgrade this tool", version)
+		glog.Errorln("error:", err)
+		return err
+	}
+
+	for i := version; i < latestDataVersion; i++ {
+		err := migrateFunctions[i](db)
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func upgrade1To2(db *bolt.DB) error {
+	fmt.Println("Upgrading v1 to v2...")
+	tx, err := db.Begin(true)
+	if err != nil {
+		return err
+	}
+	defer tx.Rollback()
+	if err := tx.Commit(); err != nil {
+		return err
+	}
+	return nil
+}