badger数据库示例用法

package main

import (
    "fmt"
    "log"
    "time"

    badger "github.com/dgraph-io/badger/v2"
)

func main() {

    // opt := badger.DefaultOptions("").WithInMemory(true) // 内存模式/无盘模式
    db, err := badger.Open(badger.DefaultOptions("./data"))
    if err != nil {
        log.Fatal(err)
    }
    defer db.Close()

    // 读写
    err = db.Update(func(txn *badger.Txn) error {
        err := txn.Set([]byte("answer"), []byte("42"))
        return err
    })

    // 只读
    err = db.View(func(txn *badger.Txn) error {
        item, err := txn.Get([]byte("answer"))
        if err != nil {
            log.Fatal(err)
        }
        var valNot, valCopy []byte
        err = item.Value(func(val []byte) error {
            // This func with val would only be called if item.Value encounters no error.

            // Accessing val here is valid.
            fmt.Printf("The answer is: %s\n", val)

            // Copying or parsing val is valid.
            valCopy = append([]byte{}, val...)

            // Assigning val slice to another variable is NOT OK.
            valNot = val // Do not do this.
            return nil
        })
        if err != nil {
            log.Fatal(err)
        }

        // DO NOT access val here. It is the most common cause of bugs.
        fmt.Printf("NEVER do this. %s\n", valNot)

        // You must copy it to use it outside item.Value(...).
        fmt.Printf("The answer is: %s\n", valCopy)

        // Alternatively, you could also use item.ValueCopy().
        valCopy, err = item.ValueCopy(nil)
        if err != nil {
            log.Fatal(err)
        }
        fmt.Printf("The answer is: %s\n", valCopy)

        return nil
    })

    // 允许在键上设置可选的生存时间（TTL）值。一旦TTL失效，该密钥将不再可检索，并且可以进行垃圾回收。可以time.Duration使用Entry.WithTTL() 和Txn.SetEntry()API方法将TTL设置为值。
    err = db.Update(func(txn *badger.Txn) error {
        e := badger.NewEntry([]byte("answer"), []byte("42")).WithTTL(time.Hour)
        err := txn.SetEntry(e)
        return err
    })
    if err != nil {
        log.Fatal(err)
    }

    // 遍历键
    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
    })
    if err != nil {
        log.Fatal(err)
    }

    // 垃圾收集
    ticker := time.NewTicker(5 * time.Minute)
    defer ticker.Stop()
    for range ticker.C {
    again:
        err := db.RunValueLogGC(0.7)
        if err == nil {
            goto again
        }
    }
}