I have created an index with: db.CreateIndex("idx", "idx

Can't get AscendGreaterOrEqual to work. about buntdb HOT 2 CLOSED

zippy commented on July 17, 2024

Can't get AscendGreaterOrEqual to work.

from buntdb.

Comments (2)

tidwall commented on July 17, 2024

CreateIndex is used to create an index on the value, not the key.

With the operation tx.Set("idx:"+idxs, msg, nil) the msg will be the value that the index is ordered against.

In your case you are appending the idx to the key.
Here's a full example using AscendGreaterOrEqual on the keys:

package main

import (
	"fmt"
	"math/rand"
	"strconv"

	"github.com/tidwall/buntdb"
)

func main() {
	db, _ := buntdb.Open(":memory:")
	// add 100 keys with the format 'key:001'
	db.Update(func(tx *buntdb.Tx) error {
		tx.CreateIndex("idx", "key:*", buntdb.IndexInt)
		for i := 0; i < 100; i++ {
			idx := strconv.Itoa(rand.Int() % 100)
			tx.Set(fmt.Sprintf("key:%03d", i), idx, nil)
		}
		return nil
	})
	// find all keys >= 'key:010'
	idx := 10
	db.View(func(tx *buntdb.Tx) error {
		tx.AscendGreaterOrEqual("", fmt.Sprintf("key:%03d", idx),
			func(key, val string) bool {
				keyidx, _ := strconv.Atoi(key[4:])
				fmt.Printf("%s %3d %3s\n", key, keyidx, val)
				return true
			},
		)
		return nil
	})
}

Here's an example using an index on the value:

package main

import (
	"fmt"
	"math/rand"
	"strconv"

	"github.com/tidwall/buntdb"
)

func main() {
	db, _ := buntdb.Open(":memory:")
	// add 100 keys with the format 'key:001'
	db.Update(func(tx *buntdb.Tx) error {
		tx.CreateIndex("idx", "key:*", buntdb.IndexInt)
		for i := 0; i < 100; i++ {
			idx := strconv.Itoa(rand.Int() % 100)
			tx.Set(fmt.Sprintf("key:%03d", i), idx, nil)
		}
		return nil
	})
	// find all values >= '10'
	idx := 10
	db.View(func(tx *buntdb.Tx) error {
		tx.AscendGreaterOrEqual("idx", strconv.Itoa(idx),
			func(key, val string) bool {
				keyidx, _ := strconv.Atoi(key[4:])
				fmt.Printf("%s %3d %3s\n", key, keyidx, val)
				return true
			},
		)
		return nil
	})
}