我想知道将由字符串键索引的二进制数据存储到单个文件中的最佳方法是什么。
这就是我要寻找的情况：
是否有任何基于 C# 的简单库可以满足这些要求？
我正在查看一些 NoSQL 数据库，但对于如此简单的数据结构来说，这似乎有点过头了。
由于在应用程序运行期间只使用了一小部分数据记录，我不希望在应用程序启动时将所有内容都读入内存（例如使用序列化），而是只从文件中读取真正需要的条目在运行时。
任何想法或提示将不胜感激，谢谢！
【问题讨论】：
使用 Binaryformater 如下代码：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
using System.Runtime.InteropServices;
using System.Runtime.Serialization.Formatters.Binary;
using System.Xml.Serialization;
namespace ConsoleApplication1
{
class Program
{
const string FILENAME = @"c:\temp\test.bin";
static void Main(string[] args)
{
Read_Write readWrite = new Read_Write();
readWrite.CreateData(1000);
readWrite.WriteData(FILENAME);
Data data = readWrite.GetRecord(FILENAME, "101");
}
}
[Serializable()]
[XmlRoot(ElementName="ABC")]
public struct Data
{
public byte[] name;
public byte[] data;
}
public class Read_Write
{
[DllImport("msvcrt.dll", CallingConvention = CallingConvention.Cdecl)]
static extern int memcmp(byte[] b1, byte[] b2, long count);
const int MIN_SIZE = 500;
const int MAX_SIZE = 10000;
public List<Data> data { get; set; }
Dictionary<string, Data> dict = new Dictionary<string, Data>();
public void CreateData(int numberRecords)
{
data = new List<Data>();
for (int i = 0; i < numberRecords; i++)
{
Data newData = new Data();
string name = i.ToString() + '\0'; //null terminate string
newData.name = Encoding.UTF8.GetBytes(name);
Random rand = new Random();
int size = rand.Next(MIN_SIZE, MAX_SIZE);
newData.data = Enumerable.Range(0, size).Select(x => (byte)(rand.Next(0, 0xFF) & 0xFF)).ToArray();
data.Add(newData);
}
}
public void WriteData(string filename)
{
Stream writer = File.OpenWrite(filename);
//write number of records
byte[] numberOfRecords = BitConverter.GetBytes((int)data.Count());
writer.Write(numberOfRecords, 0, 4);
foreach (Data d in data)
{
BinaryFormatter formatter = new BinaryFormatter();
formatter.Serialize(writer, d);
}
writer.Flush();
writer.Close();
}
public Data GetRecord(string filename, string name)
{
Data record = new Data();
Stream reader = File.OpenRead(filename);
byte[] numberOfRecords = new byte[4];
reader.Read(numberOfRecords, 0, 4);
int records = BitConverter.ToInt32(numberOfRecords, 0);
DateTime start = DateTime.Now;
for(int i = 0; i < records; i++)
{
BinaryFormatter formatter = new BinaryFormatter();
Data d = (Data)formatter.Deserialize(reader);
//if (name == GetString(d.name))
//{
// record = d;
// break;
//}
}
DateTime end = DateTime.Now;
TimeSpan time = end - start;
reader.Close();
return record;
}
public string GetString(byte[] characters)
{
int length = characters.ToList().IndexOf(0x00);
return Encoding.UTF8.GetString(characters, 0, length);
}
}
}
【讨论】：
由于似乎还没有可用的解决方案/库（可能是因为问题太简单了，无法分享 ;-)），我自己建立了一个小班。
如果其他人需要相同的，这就是我现在存储这个基于字符串键的二进制数据的方式：
internal class BinaryKeyStorage
{
private const string FILE_PATH = @"data.bin";
private static MemoryMappedFile _memoryFile;
private static MemoryMappedViewStream _memoryFileStream;
private static Dictionary<string, Entry> _index;
private class Entry
{
public Entry(int position, int length)
{
Position = position;
Length = length;
}
public int Position { get; }
public int Length { get; }
}
public static void CreateFile(Dictionary<string, byte[]> keyValues)
{
// 4 bytes for int count of entries
// and per entry:
// - string length + 1 byte for string prefix
// - 2x4 bytes for int address start and length
var headerLength = 4 + keyValues.Keys.Sum(dataKey => dataKey.Length + 9);
var nextStartPosition = headerLength;
using (var binaryWriter = new BinaryWriter(File.Open(FILE_PATH, FileMode.Create)))
{
binaryWriter.Write(keyValues.Count);
// writing header
foreach (var keyValue in keyValues)
{
binaryWriter.Write(keyValue.Key);
binaryWriter.Write(nextStartPosition);
binaryWriter.Write(keyValue.Value.Length);
nextStartPosition += keyValue.Value.Length;
}
// writing data
foreach (var keyValue in keyValues)
{
binaryWriter.Write(keyValue.Value);
}
}
}
public static List<string> GetAllKeys()
{
InitializeIndexIfNeeded();
return _index.Keys.ToList();
}
public static byte[] GetData(string key)
{
InitializeIndexIfNeeded();
var entry = _index[key];
_memoryFileStream.Seek(entry.Position, SeekOrigin.Begin);
var data = new byte[entry.Length];
_memoryFileStream.Read(data, 0, data.Length);
return data;
}
private static void InitializeIndexIfNeeded()
{
if (_memoryFile != null) return;
_memoryFile = MemoryMappedFile.CreateFromFile(FILE_PATH, FileMode.Open);
_memoryFileStream = _memoryFile.CreateViewStream();
_index = new Dictionary<string, Entry>();
using (var binaryReader = new BinaryReader(_memoryFileStream, Encoding.Default, true))
{
var count = binaryReader.ReadInt32();
for (var i = 0; i < count; i++)
{
var dataKey = binaryReader.ReadString();
var dataPosition = binaryReader.ReadInt32();
var dataLength = binaryReader.ReadInt32();
_index.Add(dataKey, new Entry(dataPosition, dataLength));
}
}
}
}
它只是将文件头/索引（字符串键以及数据的位置/长度）缓存在内存中，只有在需要时才直接从内存映射文件中读取实际数据。
【讨论】：