1、BoltDB簡介
BoltDB官方文檔如下：https://github.com/boltdb/bolt
BoltDB在Github上的說明：
Bolt是基於純Go語言開發的KV存儲，靈感來自於Howard Chu的LMDB項目。該項目目標是開發一個簡單、快速、可靠的無服務端的數據庫。API非常小巧和簡潔，僅僅關注如何獲取或設置數據，這就是全部。 BoltDB是K-V存儲，沒有關系型數據庫中類似表、行、列結構，數據以key-value對存儲（類似GO語言中的map） 。相似的key-value對存儲在同一bucket中，類似於關系型數據庫中的Table。因此，為了獲取一個value，需要知道其所在的bucket以及對應的key。
2、BoltDB常用命令
BoltDB安裝
直接在命令行使用以下命令：
$ go get github.com/boltdb/bolt/...
打開數據庫：
db, err := bolt.Open("my.db", 0600, &bolt.Options{Timeout: 1 * time.Second})
讀寫數據庫：
err := db.Update(func(tx *bolt.Tx) error {
...
return nil
})
只讀數據庫：
err := db.View(func(tx *bolt.Tx) error {
...
return nil
})
批量讀寫數據庫：
err := db.Batch(func(tx *bolt.Tx) error {
...
return nil
})
手動管理交易：
// Start a writable transaction.
tx, err := db.Begin(true)
if err != nil {
return err
}
defer tx.Rollback()
// Use the transaction...
_, err := tx.CreateBucket([]byte("MyBucket"))
if err != nil {
return err
}
// Commit the transaction and check for error.
if err := tx.Commit(); err != nil {
return err
}
使用buckets：
db.Update(func(tx *bolt.Tx) error {
b, err := tx.CreateBucket([]byte("MyBucket"))
if err != nil {
return fmt.Errorf("create bucket: %s", err)
}
return nil
})
將key/value對寫入Bucket：
db.Update(func(tx *bolt.Tx) error {
b := tx.Bucket([]byte("MyBucket"))
err := b.Put([]byte("answer"), []byte("42"))
return err
})
從Bucket中獲取value：
db.View(func(tx *bolt.Tx) error {
b := tx.Bucket([]byte("MyBucket"))
v := b.Get([]byte("answer"))
fmt.Printf("The answer is: %s\n", v)
return nil
})
在bucket中設置自增整數變量：
// CreateUser saves u to the store. The new user ID is set on u once the data is persisted.
func (s *Store) CreateUser(u *User) error {
return s.db.Update(func(tx *bolt.Tx) error {
// Retrieve the users bucket.
// This should be created when the DB is first opened.
b := tx.Bucket([]byte("users"))
// Generate ID for the user.
// This returns an error only if the Tx is closed or not writeable.
// That can't happen in an Update() call so I ignore the error check.
id, _ := b.NextSequence()
u.ID = int(id)
// Marshal user data into bytes.
buf, err := json.Marshal(u)
if err != nil {
return err
}
// Persist bytes to users bucket.
return b.Put(itob(u.ID), buf)
})
}
// itob returns an 8-byte big endian representation of v.
func itob(v int) []byte {
b := make([]byte, 8)
binary.BigEndian.PutUint64(b, uint64(v))
return b
}
type User struct {
ID int
...
}
根據key遍歷：
db.View(func(tx *bolt.Tx) error {
// Assume bucket exists and has keys
b := tx.Bucket([]byte("MyBucket"))
c := b.Cursor()
for k, v := c.First(); k != nil; k, v = c.Next() {
fmt.Printf("key=%s, value=%s\n", k, v)
}
return nil
})
cursor支持的操作方法：
First() Move to the first key. Last() Move to the last key. Seek() Move to a specific key. Next() Move to the next key. Prev() Move to the previous key.
前綴掃描：
db.View(func(tx *bolt.Tx) error {
// Assume bucket exists and has keys
c := tx.Bucket([]byte("MyBucket")).Cursor()
prefix := []byte("1234")
for k, v := c.Seek(prefix); k != nil && bytes.HasPrefix(k, prefix); k, v = c.Next() {
fmt.Printf("key=%s, value=%s\n", k, v)
}
return nil
})
區間掃描：
db.View(func(tx *bolt.Tx) error {
// Assume our events bucket exists and has RFC3339 encoded time keys.
c := tx.Bucket([]byte("Events")).Cursor()
// Our time range spans the 90's decade.
min := []byte("1990-01-01T00:00:00Z")
max := []byte("2000-01-01T00:00:00Z")
// Iterate over the 90's.
for k, v := c.Seek(min); k != nil && bytes.Compare(k, max) <= 0; k, v = c.Next() {
fmt.Printf("%s: %s\n", k, v)
}
return nil
})
ForEach()：
db.View(func(tx *bolt.Tx) error {
// Assume bucket exists and has keys
b := tx.Bucket([]byte("MyBucket"))
b.ForEach(func(k, v []byte) error {
fmt.Printf("key=%s, value=%s\n", k, v)
return nil
})
return nil
})
數據庫備份：
func BackupHandleFunc(w http.ResponseWriter, req *http.Request) {
err := db.View(func(tx *bolt.Tx) error {
w.Header().Set("Content-Type", "application/octet-stream")
w.Header().Set("Content-Disposition", `attachment; filename="my.db"`)
w.Header().Set("Content-Length", strconv.Itoa(int(tx.Size())))
_, err := tx.WriteTo(w)
return err
})
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
}
}
或者：
$ curl http://localhost/backup > my.db
統計：
go func() {
// Grab the initial stats.
prev := db.Stats()
for {
// Wait for 10s.
time.Sleep(10 * time.Second)
// Grab the current stats and diff them.
stats := db.Stats()
diff := stats.Sub(&prev)
// Encode stats to JSON and print to STDERR.
json.NewEncoder(os.Stderr).Encode(diff)
// Save stats for the next loop.
prev = stats
}
}()
只讀模式：
db, err := bolt.Open("my.db", 0666, &bolt.Options{ReadOnly: true})
if err != nil {
log.Fatal(err)
}
移動應用(iOS/Android)：
func NewBoltDB(filepath string) *BoltDB {
db, err := bolt.Open(filepath+"/demo.db", 0600, nil)
if err != nil {
log.Fatal(err)
}
return &BoltDB{db}
}
type BoltDB struct {
db *bolt.DB
...
}
func (b *BoltDB) Path() string {
return b.db.Path()
}
func (b *BoltDB) Close() {
b.db.Close()
}
Android：
String path;
if (android.os.Build.VERSION.SDK_INT >=android.os.Build.VERSION_CODES.LOLLIPOP){
path = getNoBackupFilesDir().getAbsolutePath();
} else{
path = getFilesDir().getAbsolutePath();
}
Boltmobiledemo.BoltDB boltDB = Boltmobiledemo.NewBoltDB(path)
IOS：
- (void)demo {
NSString* path = [NSSearchPathForDirectoriesInDomains(NSLibraryDirectory,
NSUserDomainMask,
YES) objectAtIndex:0];
GoBoltmobiledemoBoltDB * demo = GoBoltmobiledemoNewBoltDB(path);
[self addSkipBackupAttributeToItemAtPath:demo.path];
//Some DB Logic would go here
[demo close];
}
- (BOOL)addSkipBackupAttributeToItemAtPath:(NSString *) filePathString
{
NSURL* URL= [NSURL fileURLWithPath: filePathString];
assert([[NSFileManager defaultManager] fileExistsAtPath: [URL path]]);
NSError *error = nil;
BOOL success = [URL setResourceValue: [NSNumber numberWithBool: YES]
forKey: NSURLIsExcludedFromBackupKey error: &error];
if(!success){
NSLog(@"Error excluding %@ from backup %@", [URL lastPathComponent], error);
}
return success;
}