从 SqlDataReader 写入多个文件

Question

我创建了一个数据 reader 流，我正在尝试将结果写入文件。因为这个 table 可能会返回数百万条记录，所以我想写入多个文件，这样我就可以在文本编辑器中打开它们而不会出现问题，即。由于文件太大，文本编辑器崩溃了。这是我现在的大致情况。

using (var connection = new SqlConnection(connectionString))
using (var stream = new FileStream("directoryLocation", FileMode.Create))
{
    SqlCommand command = connection.CreateCommand();
    command.CommandText = "Select * from tblTemp";
    connection.Open();

    using(SqlDataReader reader = command.ExecuteReader())
    {
        var tableName = "tblTemp";
        var fileName = tableName + ".txt";
        var recordCount = 0;
        var fileCount = 0;

        using (StreamWriter writer = new StreamWriter(stream.Open()))
        {
            while(reader.Read())
            {
                if(recordCount == 500000)
                {
                    // Right here. Need to figure out how to close old file start new
                    recordCount = 0;
                    writer.Close();

                    fileName = tableName + "_" + (++fileCount).ToString() + ".txt";
                    writer = new StreamWriter(fileName); // I know this doesn't work. Just sudo code
                }

                recordCount++;
                writer.WriterLine(recordInfo); // recordInfo is sudo code as well
            }
        }
    }
}

我不想将 using writer 语句移动到 reader 循环中，因为这会打开和关闭每条记录的文件连接。关于如何保持我在 reader 中的位置以及仅在需要时打开和关闭文件有什么想法吗？

Answer 1

你很接近。您不需要单独的 FileStream。可以在循环中间创建一个新的 StreamWriter，只要您根据需要处理前一个 StreamWriter。

using (var connection = new SqlConnection(connectionString))
{
    SqlCommand command = connection.CreateCommand();
    command.CommandText = "Select * from tblTemp";
    connection.Open();

    using(SqlDataReader reader = command.ExecuteReader())
    {
        var tableName = "tblTemp";
        var fileName = tableName + ".txt";
        var recordCount = 0;
        var fileCount = 0;

        StreamWriter writer = null;
        try
        {
            while (reader.Read())
            {
                if (writer == null || recordCount == 500000)
                {
                    recordCount = 0;

                    // Close the previous file if it is open...
                    if (writer != null)
                    {
                        writer.Close();
                        writer.Dispose();
                    }

                    fileName = tableName + "_" + (++fileCount).ToString() + ".txt";

                    // Open the new file...
                    writer = new StreamWriter(fileName);
                }

                recordCount++;
                writer.WriterLine(recordInfo); // recordInfo is sudo code as well
            }
        }
        finally
        {
            // Make sure the file gets closed...
            if (writer != null)
            {
                writer.Dispose();
            }
        }
    }
}

Answer 2

就我个人而言，我会使用 TextWriter 的自定义覆盖来分离将文件名滚动到代码之外的逻辑。像这样的东西完全未经测试，可能不是线程安全的，效率低下（目前它一次只能写一个字符！），并且可能有错误代码：

public class RollingFileWriter : TextWriter
{
    private readonly string _filenamePrefix;
    private readonly string _fileNameSuffix;
    private readonly int _maxRecordCount;
    private Stream _innerStream;
    private int _recordCount = 0;
    private int _fileCounter = 0;

    public RollingFileWriter( string filenamePrefix, string fileNameSuffix = ".txt", int maxRecordCount = 500000 )
    {
        _filenamePrefix = filenamePrefix;
        _fileNameSuffix = fileNameSuffix;
        _maxRecordCount = maxRecordCount;

        _innerStream = new FileStream(
            _filenamePrefix + "_" + _fileCounter.ToString() + _fileNameSuffix,
            FileMode.Create );
    }

    public override Encoding Encoding
    {
        get { return Encoding.UTF8; }
    }

    public override void Write( char value )
    {
        _innerStream.Write( Encoding.GetBytes( new[] { value } ), 0, 1 );
    }

    public override void WriteLine( string value )
    {
        if ( ++_recordCount == _maxRecordCount )
        {
            SwitchStreams();
        }
        base.WriteLine( value );
    }

    private void SwitchStreams()
    {
        _innerStream.Close();
        _innerStream.Dispose();

        _innerStream = new FileStream(
            _filenamePrefix + "_" + ( ++_fileCounter ).ToString() + _fileNameSuffix,
            FileMode.Create );
        _recordCount = 0;
    }

    protected override void Dispose( bool disposing )
    {
        if ( disposing )
        {
            _innerStream.Dispose();
        }
    }
}

然后你可以去掉外面的FileStream，用RollingFileWriter替换里面的StreamWriter，并从循环中删除所有其他逻辑。

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