C# 使用 BerkeleyDB（四）：游標遍歷 Find 實現

Find 方法

public List Find()
{
    var list = new List();
    using (var cursor = _btree.OpenCursor(_txn, DbFileCursor.CreateFlags.None))
    {
        IPut item = null;
        while (GetNextRecord(cursor, ref item))
            list.Add(item);
    }
    return list;
}

GetNextRecord 核心邏輯

bool GetNextRecord(DbBTreeCursor cursor, ref IPut item)
{
    ReadStatus status;
    _keyStream.SetLength(_keyStream.Capacity);
    _dataStream.SetLength(_dataStream.Capacity);
    DbEntry key = DbEntry.Out(_keyStream.GetBuffer());
    DbEntry data = DbEntry.Out(_dataStream.GetBuffer());

    do
    {
        status = cursor.Get(ref key, ref data, DbFileCursor.GetMode.Next, DbFileCursor.ReadFlags.None);
        switch (status)
        {
            case ReadStatus.NotFound: return false;
            case ReadStatus.KeyEmpty: continue; // 跳過已刪除
            case ReadStatus.BufferSmall:
                if (key.Buffer.Length < key.Size) { _keyStream.SetLength(key.Size); key = DbEntry.Out(_keyStream.GetBuffer()); }
                if (data.Buffer.Length < data.Size) { _dataStream.SetLength(data.Size); data = DbEntry.Out(_dataStream.GetBuffer()); }
                continue;
            case ReadStatus.Success:
                _dataStream.Position = 0;
                _dataStream.SetLength(data.Size);
                item = (IPut)_formatter.Deserialize(_dataStream);
                return true;
            default: return false;
        }
    } while (true);
}

關鍵點

• DbEntry.Out 僅提供輸出緩衝區，BufferSmall 時需根據 Size 屬性擴容流並重新包裝。
• KeyEmpty 表示槽位存在但已刪除，需 continue 跳過。
• 反序列化前必須 Position=0 並 SetLength(data.Size) 截取有效字節。
• using 確保游標釋放。