golang LMDB入门例子——key range查询

package main


import (
    "bytes"
    "fmt"
    "io/ioutil"
    "os"
    . "github.com/szferi/gomdb"
)

// Most mdb functions/methods can return errors. This example ignores errors
// for brevity. Real code should check all return values.
func main() {
    // create a directory to hold the database
    path, _ := ioutil.TempDir("", "mdb_test")
    defer os.RemoveAll(path)

    // open the db
    env, _ := NewEnv()
    env.SetMapSize(1 << 20) // max file size
    env.Open(path, 0, 0664)
    defer env.Close()
    txn, _ := env.BeginTxn(nil, 0)
    dbi, _ := txn.DBIOpen(nil, 0)
    defer env.DBIClose(dbi)
    txn.Commit()

    // write some data
    txn, _ = env.BeginTxn(nil, 0)
    num_entries := 10
    for i := 0; i < num_entries; i++ {
        key := fmt.Sprintf("Key-%d", i)
        val := fmt.Sprintf("Val-%d", i)
        txn.Put(dbi, []byte(key), []byte(val), 0)
    }
    txn.Commit()

    // inspect the database
    stat, _ := env.Stat()
    fmt.Println(stat.Entries)

    // scan the database
    txn, _ = env.BeginTxn(nil, RDONLY)
    defer txn.Abort()
    cursor, _ := txn.CursorOpen(dbi)
    defer cursor.Close()
    for {
        bkey, bval, err := cursor.Get(nil, nil, NEXT)
        if err == NotFound {
            break
        }
        if err != nil {
            panic(err)
        }
        fmt.Printf("%s: %s\n", bkey, bval)
    }

    // random access
    bval, _ := txn.Get(dbi, []byte("Key-3"))
    fmt.Println(string(bval))

    fmt.Printf("*********range begin*********\n")
    bkey := []byte("Key-2")
    bkeyEnd := []byte("Key-5")
    // var MDB_SET_RANGE uint = 17
    // var op = MDB_SET_RANGE

    var op uint = SET_RANGE
    for {
        bkey, bval, err := cursor.Get(bkey, nil, op)
        if err == NotFound || bytes.Compare(bkey, bkeyEnd) > 0 {
            break
        }
        if err != nil {
            panic(err)
        }
        fmt.Printf("%s: %s\n", bkey, bval)
        op = NEXT
    }
    fmt.Printf("**********range end********\n")
}