Как преобразовать XML как строку w/o использование файлов в.NET?

Мне потребовалось много времени (буквально годы), чтобы понять, насколько лаконичным может быть код с использованием Stream и/или TextWriter, если использовать правильные идиомы.

Предполагая, что transform и input являются строками:

StringWriter sw = new StringWriter();
using (XmlReader xrt = XmlReader.Create(new StringReader(transform))
using (XmlReader xri = XmlReader.Create(new StringReader(input))
using (XmlWriter xwo = XmlWriter.Create(sw))
{
   XslCompiledTransform xslt = new XslCompiledTransform();
   xslt.Load(xrt);
   xslt.Transform(xri, xwo);
}
string output = sw.ToString();

Вы можете XmlReader.Create () из StringReader или MemoryStream . XslCompileTransfrom может Load () из XmlReader .

Я бы использовал перегрузки XmlReader.Create (DatabaseBlobStream) и XmlWriter.Create (StringBuilder) . Использование следующего объекта DatabaseBlobStream

DatabaseBlobStream.cs

internal class DatabaseBlobStream : Stream
{
    private readonly IDataReader reader;
    private readonly int columnIndex;
    private long streamPosition;

    internal DatabaseBlobStream(IDataReader reader, int columnIndex)
    {
        this.reader = reader;
        this.columnIndex = columnIndex;
    }

    public override bool CanRead
    {
        get
        {
            return reader.GetFieldType(columnIndex) == typeof (byte[])
                   && !reader.IsDBNull(columnIndex);
        }
    }

    public override bool CanSeek
    {
        get { return false; }
    }

    public override bool CanWrite
    {
        get { return false; }
    }

    public override void Flush()
    {
        throw new Exception("This stream does not support writing.");
    }

    public override long Length
    {
        get { throw new Exception("This stream does not support the Length property."); }
    }

    public override long Position
    {
        get
        {
            return streamPosition;
        }
        set
        {
            streamPosition = value;
        }
    }

    public override int Read(byte[] buffer, int offset, int count)
    {
        if (reader.IsDBNull(columnIndex))
            return 0;

        int bytesRead = (int)reader.GetBytes(columnIndex, streamPosition + offset, buffer, 0, count);
        streamPosition += bytesRead;
        return bytesRead;
    }

    public override long Seek(long offset, SeekOrigin origin)
    {
        throw new Exception("This stream does not support seeking.");
    }

    public override void SetLength(long value)
    {
        throw new Exception("This stream does not support setting the Length.");
    }

    public override void Write(byte[] buffer, int offset, int count)
    {
        throw new Exception("This stream does not support writing.");
    }

    public override void Close()
    {
        try
        {
            reader.Close();
        }
        finally
        {
            base.Close();
        }
    }

    protected override void Dispose(bool disposing)
    {
        try
        {
            reader.Dispose();
        }
        finally
        {
            base.Dispose(disposing);
        }
    }
}

edit: using-blocks added

// input-xml
string xmlinput = String.Empty;
// xslt
string xsltinput = String.Empty;
// output-xml
string xmloutput = String.Empty;

// Prepare input-xml
XPathDocument doc = new XPathDocument(new StringReader(xmlinput));

// Prepare XSLT
XslTransform xslt = new XslTransform();
// Creates a XmlReader from your xsl string
using (XmlReader xmlreader = XmlReader.Create(new StringReader(xsltinput)))
{
    //Load the stylesheet.
    xslt.Load(xmlreader);

    // transform
    using (StringWriter sw = new StringWriter())
    {
        xslt.Transform(doc, null, sw);

        // save to string
        xmloutput = sw.ToString();
    }
}