Using StringWriter for XML Serialization

Question

I'm currently searching for an easy way to serialize objects (in C# 3).

I googled some examples and came up with something like:

MemoryStream memoryStream = new MemoryStream ( ); XmlSerializer xs = new XmlSerializer ( typeof ( MyObject) ); XmlTextWriter xmlTextWriter = new XmlTextWriter ( memoryStream, Encoding.UTF8 ); xs.Serialize ( xmlTextWriter, myObject); string result = Encoding.UTF8.GetString(memoryStream .ToArray()); 

After reading this question I asked myself, why not using StringWriter? It seems much easier.

XmlSerializer ser = new XmlSerializer(typeof(MyObject)); StringWriter writer = new StringWriter(); ser.Serialize(writer, myObject); serializedValue = writer.ToString(); 

Another Problem was, that the first example generated XML I could not just write into an XML column of SQL Server 2005 DB.

The first question is: Is there a reason why I shouldn't use StringWriter to serialize an Object when I need it as a string afterwards? I never found a result using StringWriter when googling.

The second is, of course: If you should not do it with StringWriter (for whatever reasons), which would be a good and correct way?

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Addition:

As it was already mentioned by both answers, I'll further go into the XML to DB problem.

When writing to the Database I got the following exception:

System.Data.SqlClient.SqlException: XML parsing: line 1, character 38, unable to switch the encoding

For string

<?xml version="1.0" encoding="utf-8"?><test/> 

I took the string created from the XmlTextWriter and just put as xml there. This one did not work (neither with manual insertion into the DB).

Afterwards I tried manual insertion (just writing INSERT INTO ... ) with encoding="utf-16" which also failed. Removing the encoding totally worked then. After that result I switched back to the StringWriter code and voila - it worked.

Problem: I don't really understand why.

at Christian Hayter: With those tests I'm not sure that I have to use utf-16 to write to the DB. Wouldn't setting the encoding to UTF-16 (in the xml tag) work then?

Answer 1

One problem with StringWriter is that by default it doesn't let you set the encoding which it advertises - so you can end up with an XML document advertising its encoding as UTF-16, which means you need to encode it as UTF-16 if you write it to a file. I have a small class to help with that though:

public sealed class StringWriterWithEncoding : StringWriter {     public override Encoding Encoding { get; }      public StringWriterWithEncoding (Encoding encoding)     {         Encoding = encoding;     }     } 

Or if you only need UTF-8 (which is all I often need):

public sealed class Utf8StringWriter : StringWriter {     public override Encoding Encoding => Encoding.UTF8; } 

As for why you couldn't save your XML to the database - you'll have to give us more details about what happened when you tried, if you want us to be able to diagnose/fix it.

Answer 2

When serialising an XML document to a .NET string, the encoding must be set to UTF-16. Strings are stored as UTF-16 internally, so this is the only encoding that makes sense. If you want to store data in a different encoding, you use a byte array instead.

SQL Server works on a similar principle; any string passed into an xml column must be encoded as UTF-16. SQL Server will reject any string where the XML declaration does not specify UTF-16. If the XML declaration is not present, then the XML standard requires that it default to UTF-8, so SQL Server will reject that as well.

Bearing this in mind, here are some utility methods for doing the conversion.

public static string Serialize<T>(T value) {      if(value == null) {         return null;     }      XmlSerializer serializer = new XmlSerializer(typeof(T));      XmlWriterSettings settings = new XmlWriterSettings()     {         Encoding = new UnicodeEncoding(false, false), // no BOM in a .NET string         Indent = false,         OmitXmlDeclaration = false     };      using(StringWriter textWriter = new StringWriter()) {         using(XmlWriter xmlWriter = XmlWriter.Create(textWriter, settings)) {             serializer.Serialize(xmlWriter, value);         }         return textWriter.ToString();     } }  public static T Deserialize<T>(string xml) {      if(string.IsNullOrEmpty(xml)) {         return default(T);     }      XmlSerializer serializer = new XmlSerializer(typeof(T));      XmlReaderSettings settings = new XmlReaderSettings();     // No settings need modifying here      using(StringReader textReader = new StringReader(xml)) {         using(XmlReader xmlReader = XmlReader.Create(textReader, settings)) {             return (T) serializer.Deserialize(xmlReader);         }     } }