badger_seek.go

package main

import (
	"fmt"
	"log"

	badger "github.com/dgraph-io/badger/v3"
)

func main() {
	log.Println("Creating updates")
	opts := badger.DefaultOptions("").WithInMemory(true)
	// Open the Badger database located in the /tmp/badger directory.
	// It will be created if it doesn't exist.
	db, err := badger.Open(opts)
	if err != nil {
		log.Fatal(err)
	}
	defer db.Close()
	log.Println("Creating updates")
	updates := map[string]string{
		"aaaa": "",
		"aaab": "",
		"aabb": "",
		"abbb": "",
		"bbbb": "",
	}
	txn := db.NewTransaction(true)
	for k, v := range updates {
		if err := txn.Set([]byte(k), []byte(v)); err == badger.ErrTxnTooBig {
			_ = txn.Commit()
			txn = db.NewTransaction(true)
			_ = txn.Set([]byte(k), []byte(v))
		}
	}
	_ = txn.Commit()

	log.Println("Iterating over the entire dataset")

	err = db.View(func(txn *badger.Txn) error {
		opts := badger.DefaultIteratorOptions
		opts.PrefetchSize = 10
		it := txn.NewIterator(opts)
		defer it.Close()
		for it.Rewind(); it.Valid(); it.Next() {
			item := it.Item()
			k := item.Key()
			err := item.Value(func(v []byte) error {
				fmt.Printf("key=%s, value=%s\n", k, v)
				return nil
			})
			if err != nil {
				return err
			}
		}
		return nil
	})
	log.Println("Let's jump to \"aabb\" and continue forward...")

	err = db.View(func(txn *badger.Txn) error {
		opts := badger.DefaultIteratorOptions
		opts.PrefetchSize = 10
		it := txn.NewIterator(opts)
		defer it.Close()
		for it.Seek([]byte("aabb")); it.ValidForPrefix([]byte("")); it.Next() {
			item := it.Item()
			k := item.Key()
			err := item.Value(func(v []byte) error {
				fmt.Printf("key=%s, value=%s\n", k, v)
				return nil
			})
			if err != nil {
				return err
			}
		}
		return nil
	})

	log.Println("Let's jump to \"aa\" and scan with prefix \"aa\"")

	err = db.View(func(txn *badger.Txn) error {
		opts := badger.DefaultIteratorOptions
		opts.PrefetchSize = 10
		it := txn.NewIterator(opts)
		defer it.Close()
		for it.Seek([]byte("aa")); it.ValidForPrefix([]byte("aa")); it.Next() {
			item := it.Item()
			k := item.Key()
			err := item.Value(func(v []byte) error {
				fmt.Printf("key=%s, value=%s\n", k, v)
				return nil
			})
			if err != nil {
				return err
			}
		}
		return nil
	})

}