testbadger.go

// Test code to show the Badger MergeOperator merging the deleted previous value with the new added values

func add(originalValue, newValue []byte) []byte {
	return append(originalValue, newValue...)
}

func main() {
	opts := badger.DefaultOptions("./testdata")
	db, err := badger.Open(opts)
	if err != nil {
		println("Error opening badger db" + err.Error())
		return
	}
	defer db.Close()

	m := db.GetMergeOperator([]byte("mykey"), add, 200*time.Millisecond)

	m.Add([]byte("initial value."))
	m.Add([]byte(" Additioal value."))
	m.Stop()

	time.Sleep(time.Second)

	err = db.View(func(txn *badger.Txn) error {
		item, err := txn.Get([]byte("mykey"))
		if err != nil {
			return err
		}

		item.Value(func(val []byte) error {
			fmt.Printf("Value: %v\n", string(val)) //-->This prints the value "initial value. Additional value." as expected
			return nil
		})
		return nil
	})

	// Delete the merged value
	db.Update(func(txn *badger.Txn) error {
		return txn.Delete([]byte("mykey"))
	})

	mnew := db.GetMergeOperator([]byte("mykey"), add, 200*time.Millisecond)
	mnew.Add([]byte("new value."))
	mnew.Add([]byte(" Additional new value."))
	mnew.Stop()

	time.Sleep(time.Second)

	err = db.View(func(txn *badger.Txn) error {
		item, err := txn.Get([]byte("mykey"))
		if err != nil {
			return err
		}

		item.Value(func(val []byte) error {
			//-->I expect this to print only "new value. Additional new value." as the previous value is deleted.
			// But, this prints "initial value. Additional value.new value. Additional new value"
			fmt.Printf("Value: %v\n", string(val))
			return nil
		})
		return nil
	})

}