Migrate BadgerDB v1 to BadgerDB v2 programatically

main.go

package main

import (
	"flag"
	"log"

	bv1 "github.com/dgraph-io/badger"
	bv2 "github.com/dgraph-io/badger/v2"
)

var (
	oldDir = flag.String("i", "", "input database (v1)")
	newDir = flag.String("o", "", "output database (v2)")
)

// usage: go run main.go -i "v1 db path" -o "v2 db path"
func main() {
	flag.Parse()

	if *oldDir == "" {
		log.Fatal("old database (v1) path cannot be empty")
	}

	if *newDir == "" {
		log.Fatal("new database (v2) path cannot be empty")
	}

	v1opts := bv1.DefaultOptions(*oldDir)
	odb, err := bv1.Open(v1opts)
	if err != nil {
		log.Fatal(err)
	}
	defer odb.Close()

	v2opts := bv2.DefaultOptions(*newDir)
	ndb, err := bv2.Open(v2opts)
	if err != nil {
		log.Fatal(err)
	}
	defer ndb.Close()

	if err := ndb.Update(func(utxn *bv2.Txn) error {
		return odb.View(func(vtxn *bv1.Txn) error {
			it := vtxn.NewIterator(bv1.DefaultIteratorOptions)
			defer it.Close()

			if it.Rewind(); it.Valid() {
				if err := it.Item().Value(func(val []byte) error {
					return utxn.Set(it.Item().Key(), val)
				}); err != nil {
					return err
				}
			}

			for {
				if it.Next(); it.Valid() {
					if err := it.Item().Value(func(val []byte) error {
						return utxn.Set(it.Item().Key(), val)
					}); err != nil {
						return err
					}
				} else {
					break
				}
			}

			return nil
		})
	}); err != nil {
		log.Fatal(err)
	}
}