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     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   lt  xml version  1 0  encoding  utf-8   gt  lt test  gt    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

User · Answer

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   gt  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

User · Answer

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 lt T gt  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 lt T gt  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

User · Answer

It may have been covered elsewhere but simply changing the encoding line of the XML source to  utf-16  allows the XML to be inserted into a SQL Server  xml data type     using  DataSetTableAdapters SQSTableAdapter tbl SQS   new DataSetTableAdapters SQSTableAdapter          try               bodyXML      lt  xml version  1 0  encoding  UTF-8  standalone  yes   gt  lt test gt  lt  test gt            bodyXMLutf16   bodyXML Replace  UTF-8    UTF-16            tbl SQS Insert messageID  receiptHandle  md5OfBody  bodyXMLutf16  sourceType             catch  System Data SqlClient SqlException ex                Console WriteLine ex Message           Console ReadLine              The result is all of the XML text is inserted into the  xml  data type field but the  header  line is removed   What you see in the resulting record is just    lt test gt  lt  test gt    Using the serialization method described in the  Answered  entry is a way of including the original header in the target field but the result is that the remaining XML text is enclosed in an XML  lt string gt  lt  string gt  tag   The table adapter in the code is a class automatically built using the Visual Studio 2013  Add New Data Source  wizard   The five parameters to the Insert method map to fields in a SQL Server table

User · Answer

public static T DeserializeFromXml lt T gt  string xml        T result      XmlSerializerFactory serializerFactory   new XmlSerializerFactory        XmlSerializer serializer  serializerFactory CreateSerializer typeof T         using  StringReader sr3   new StringReader xml                 XmlReaderSettings settings   new XmlReaderSettings                         CheckCharacters   false    default value is true                      using  XmlReader xr3   XmlTextReader Create sr3  settings                         result    T serializer Deserialize xr3                        return result

User · Answer

lt TL DR gt  The problem is rather simple  actually  you are not matching the declared encoding  in the XML declaration  with the datatype of the input parameter  If you manually added  lt  xml version  1 0  encoding  utf-8   gt  lt test  gt  to the string  then declaring the SqlParameter to be of type SqlDbType Xml or SqlDbType NVarChar would give you the  unable to switch the encoding  error  Then  when inserting manually via T-SQL  since you switched the declared encoding to be utf-16  you were clearly inserting a VARCHAR string  not prefixed with an upper-case  N   hence an 8-bit encoding  such as UTF-8  and not an NVARCHAR string  prefixed with an upper-case  N   hence the 16-bit UTF-16 LE encoding    The fix should have been as simple as    In the first case  when adding the declaration stating encoding  utf-8   simply don t add the XML declaration  In the second case  when adding the declaration stating encoding  utf-16   either   simply don t add the XML declaration  OR simply add an  N  to the input parameter type  SqlDbType NVarChar instead of SqlDbType VarChar  -   or possibly even switch to using SqlDbType Xml      Detailed response is below     All of the answers here are over-complicated and unnecessary  regardless of the 121 and 184 up-votes for Christian s and Jon s answers  respectively   They might provide working code  but none of them actually answer the question  The issue is that nobody truly understood the question  which ultimately is about how the XML datatype in SQL Server works  Nothing against those two clearly intelligent people  but this question has little to nothing to do with serializing to XML  Saving XML data into SQL Server is much easier than what is being implied here   It doesn t really matter how the XML is produced as long as you follow the rules of how to create XML data in SQL Server  I have a more thorough explanation  including working example code to illustrate the points outlined below  in an answer on this question  How to solve    unable to switch the encoding    error when inserting XML into SQL Server  but the basics are    The XML declaration is optional The XML datatype stores strings always as UCS-2   UTF-16 LE If your XML is UCS-2   UTF-16 LE  then you    pass in the data as either NVARCHAR MAX  or XML   SqlDbType NVarChar  maxsize   -1  or SqlDbType Xml  or if using a string literal then it must be prefixed with an upper-case  N   if specifying the XML declaration  it must be either  UCS-2  or  UTF-16   no real difference here   If your XML is 8-bit encoded  e g   UTF-8     iso-8859-1     Windows-1252    then you    need to specify the XML declaration IF the encoding is different than the code page specified by the default Collation of the database you must pass in the data as VARCHAR MAX    SqlDbType VarChar  maxsize   -1   or if using a string literal then it must not be prefixed with an upper-case  N   Whatever 8-bit encoding is used  the  encoding  noted in the XML declaration must match the actual encoding of the bytes  The 8-bit encoding will be converted into UTF-16 LE by the XML datatype    With the points outlined above in mind  and given that strings in  NET are always UTF-16 LE   UCS-2 LE  there is no difference between those in terms of encoding   we can answer your questions      Is there a reason why I shouldn t use StringWriter to serialize an Object when I need it as a string afterwards    No  your StringWriter code appears to be just fine  at least I see no issues in my limited testing using the 2nd code block from the question       Wouldn t setting the encoding to UTF-16  in the xml tag  work then    It isn t necessary to provide the XML declaration  When it is missing  the encoding is assumed to be UTF-16 LE if you pass the string into SQL Server as NVARCHAR  i e  SqlDbType NVarChar  or XML  i e  SqlDbType Xml   The encoding is assumed to be the default 8-bit Code Page if passing in as VARCHAR  i e  SqlDbType VarChar   If you have any non-standard-ASCII characters  i e  values 128 and above  and are passing in as VARCHAR  then you will likely see     for BMP characters and      for Supplementary Characters as SQL Server will convert the UTF-16 string from  NET into an 8-bit string of the current Database s Code Page before converting it back into UTF-16   UCS-2  But you shouldn t get any errors   On the other hand  if you do specify the XML declaration  then you must pass into SQL Server using the matching 8-bit or 16-bit datatype  So if you have a declaration stating that the encoding is either UCS-2 or UTF-16  then you must pass in as SqlDbType NVarChar or SqlDbType Xml  Or  if you have a declaration stating that the encoding is one of the 8-bit options  i e  UTF-8  Windows-1252  iso-8859-1  etc   then you must pass in as SqlDbType VarChar  Failure to match the declared encoding with the proper 8 or 16 -bit SQL Server datatype will result in the  unable to switch the encoding  error that you were getting   For example  using your StringWriter-based serialization code  I simply printed the resulting string of the XML and used it in SSMS  As you can see below  the XML declaration is included  because StringWriter does not have an option to OmitXmlDeclaration like XmlWriter does   which poses no problem so long as you pass the string in as the correct SQL Server datatype   -- Upper-case  N  prefix    NVARCHAR  hence no error  DECLARE  Xml XML   N  lt  xml version  1 0  encoding  utf-16   gt   lt string gt Test   lt  string gt    SELECT  Xml  --  lt string gt Test   lt  string gt    As you can see  it even handles characters beyond standard ASCII  given that   is BMP Code Point U 1234  and  is Supplementary Character Code Point U 1F638  However  the following   -- No upper-case  N  prefix on the string literal  hence VARCHAR  DECLARE  Xml XML     lt  xml version  1 0  encoding  utf-16   gt   lt string gt Test   lt  string gt      results in the following error   Msg 9402  Level 16  State 1  Line XXXXX XML parsing  line 1  character 39  unable to switch the encoding     Ergo  all of that explanation aside  the full solution to your original question is   You were clearly passing the string in as SqlDbType VarChar  Switch to SqlDbType NVarChar and it will work without needing to go through the extra step of removing the XML declaration  This is preferred over keeping SqlDbType VarChar and removing the XML declaration because this solution will prevent data loss when the XML includes non-standard-ASCII characters  For example   -- No upper-case  N  prefix on the string literal    VARCHAR  and no XML declaration  DECLARE  Xml2 XML     lt string gt Test   lt  string gt    SELECT  Xml2  --  lt string gt Test     lt  string gt    As you can see  there is no error this time  but now there is data-loss   x1F640

User · Answer

First of all  beware of finding old examples  You ve found one that uses XmlTextWriter  which is deprecated as of  NET 2 0  XmlWriter Create should be used instead   Here s an example of serializing an object into an XML column   public void SerializeToXmlColumn object obj        using  var outputStream   new MemoryStream                  using  var writer   XmlWriter Create outputStream                         var serializer   new XmlSerializer obj GetType                 serializer Serialize writer  obj                      outputStream Position   0          using  var conn   new SqlConnection Settings Default ConnectionString                         conn Open                 const string INSERT COMMAND     INSERT INTO XmlStore  Data  VALUES   Data                using  var cmd   new SqlCommand INSERT COMMAND  conn                                 using  var reader   XmlReader Create outputStream                                         var xml   new SqlXml reader                        cmd Parameters Clear                        cmd Parameters AddWithValue   Data   xml                       cmd ExecuteNonQuery

[c#] Using StringWriter for XML Serialization

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