diff --git a/README.md b/README.md index 53dcc40..97a5037 100644 --- a/README.md +++ b/README.md @@ -268,6 +268,50 @@ transaction is open. If you need to use a value outside of the transaction then you must use `copy()` to copy it to another byte slice. +### Autoincrementing integer for the bucket +By using the NextSequence() function, you can let Bolt determine a sequence +which can be used as the unique identifier for your key/value pairs. See the +example below. + +```go +// 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 + ... +} + +``` + ### Iterating over keys Bolt stores its keys in byte-sorted order within a bucket. This makes sequential