在现代软件开发中，经常需要在文件系统和数据库之间进行数据的读写操作。本文将介绍一种在C#中实现文件和SQL Server数据库之间文本数据交互的方法。将设计一个统一的接口，并提供两种实现方式：一种是针对C#文本流的实现，另一种是针对SQL Server数据库的实现。
为了实现文件和数据库之间的文本数据交互，首先设计了一个统一的接口ICharsHandler。这个接口定义了三个方法：GetChars用于从源读取数据块，PutChars用于将数据块写入目标，Close用于释放资源。
public interface ICharsHandler {
char[] GetChars(long offset, int length); // 读取数据块
void PutChars(long offset, char[] buffer); // 写入数据块
void Close(); // 释放资源
}
对于C#文本流的实现，创建了一个名为StreamTextHandler的类，它实现了ICharsHandler接口。这个类使用TextReader和TextWriter来分别处理读取和写入操作。
public class StreamTextHandler : ICharsHandler {
TextReader reader;
TextWriter writer;
char[] buffer;
public StreamTextHandler(TextWriter wr, TextReader rd) {
reader = rd;
writer = wr;
}
public char[] GetChars(long offset, int length) {
if (reader == null) throw new InvalidOperationException("Can't read data");
if (buffer == null || buffer.Length != length) buffer = new char[length];
int cnt = reader.Read(buffer, (int)offset, length);
if (cnt < length) {
char[] nv = new char[cnt];
Array.Copy(buffer, nv, cnt);
return nv;
}
return buffer;
}
public void PutChars(long offset, char[] buffer) {
if (writer == null) throw new InvalidOperationException("Can't write data");
writer.Write(buffer, (int)offset, buffer.Length);
}
public void Close() {
if (reader != null) reader.Close();
if (writer != null) writer.Close();
}
}
对于SQL Server数据库的实现，创建了一个名为SqlTextHandler的类，它同样实现了ICharsHandler接口。这个类使用SqlCommand来执行数据库的读取和写入操作。
class SqlTextHandler : ICharsHandler {
SqlCommand readCommand;
SqlCommand writeCommand;
int column;
SqlDataReader rd;
bool previousConn = false;
public SqlTextHandler(SqlCommand cmd, SqlCommand wr, int _column) {
readCommand = cmd;
writeCommand = wr;
column = _column;
previousConn = (wr != null) ? wr.Connection.State == ConnectionState.Open : cmd.Connection.State == ConnectionState.Open;
}
protected void OpenReader() {
readCommand.Connection.Open();
rd = readCommand.ExecuteReader(CommandBehavior.SequentialAccess | CommandBehavior.SingleRow);
rd.Read();
}
protected void OpenWriter() {
SqlParameter Out = writeCommand.Parameters.Add("@Value", SqlDbType.NVarChar);
SqlParameter OffsetParam = writeCommand.Parameters.Add("@Offset", SqlDbType.BigInt);
SqlParameter LengthParam = writeCommand.Parameters.Add("@Length", SqlDbType.Int);
writeCommand.Connection.Open();
}
char[] buffer;
public char[] GetChars(long offset, int length) {
if (rd == null) OpenReader();
if (buffer == null || buffer.Length != length) {
buffer = new char[length];
}
long cnt = rd.GetChars(column, offset, buffer, 0, length);
if (cnt < length) {
char[] nv = new char[cnt];
Array.Copy(buffer, nv, cnt);
return nv;
}
return buffer;
}
public void PutChars(long offset, char[] buffer) {
if (writeCommand.Parameters.Count < 4) OpenWriter();
writeCommand.Parameters["@Length"].Value = buffer.Length;
writeCommand.Parameters["@Value"].Value = buffer;
writeCommand.Parameters["@Offset"].Value = offset;
writeCommand.ExecuteNonQuery();
}
public void Close() {
if (rd != null) rd.Close();
if (!previousConn) {
if (readCommand != null) readCommand.Connection.Close();
if (writeCommand != null) writeCommand.Connection.Close();
}
}
}
void MoveText(ICharHandler source, ICharHandler target) {
long offset = 0;
for (;;) {
char[] buffer = source.GetChars(offset, BUFFER_SIZE);
target.PutChars(offset, buffer);
if (buffer.Length < BUFFER_SIZE) break;
offset += BUFFER_SIZE;
}
}