example_lmdb_test.go1

package lex_test

import (
	"bytes"
	"fmt"
	"io/ioutil"
	"os"
	"github.com/xcdb/lex"

	lmdb "github.com/szferi/gomdb"
)

type planet struct {
	Name     string
	Distance float32 //AU
	Mass     float32 //Earth masses
}

func setupLmdb() *lmdb.Env {
	path, _ := ioutil.TempDir("", "lex_lmdb_example")
	env, _ := lmdb.NewEnv()
	env.Open(path, 0, 0664)
	return env
}

func cleanLmdb(env *lmdb.Env) {
	env.Close()
	path, _ := env.Path()
	os.RemoveAll(path)
}

func ExampleLmdb() {
	//from https://en.wikipedia.org/wiki/Solar_System
	planets := []planet{
		{"Mercury", 0.4, 0.55},
		{"Venus", 0.7, 0.815},
		{"Earth", 1, 1},
		{"Mars", 1.5, 0.107},
		{"Jupiter", 5.2, 318},
		{"Saturn", 9.5, 95},
		{"Uranus", 19.2, 14},
		{"Neptune", 30.1, 17},
	}

	env := setupLmdb()
	defer cleanLmdb(env)

	//index of {distance} => name
	txn, _ := env.BeginTxn(nil, 0)
	dbi, _ := txn.DBIOpen(nil, 0)
	defer env.DBIClose(dbi)
	txn.Commit()

	txn, _ = env.BeginTxn(nil, 0)
	for _, p := range planets {
		k, _ := lex.Key(p.Distance)
		v := []byte(p.Name)
		txn.Put(dbi, k, v, 0)
	}
	txn.Commit()

	//range seek on float key
	//find planets in the goldilocks zone (0.9AU to 1.5AU)
	min, _ := lex.Key(float32(0.9))
	max, _ := lex.Key(float32(1.5))

	txn, _ = env.BeginTxn(nil, lmdb.RDONLY)
	defer txn.Abort()
	c, _ := txn.CursorOpen(dbi)
	defer c.Close()

	for k, v, err := c.Get(min, nil, lmdb.SET_RANGE); err != lmdb.NotFound && bytes.Compare(k, max) <= 0; k, v, err = c.Get(nil, nil, lmdb.NEXT) {
		fmt.Printf("%v\n", string(v))
	}

	//Output:
	//Earth
	//Mars
}