DataTable implements IXmlSerializable, and the schema for the DataTable is unique enough allowing wsdl.exe to take advantage of the new feature (SchemaImporterExtension) to generate DataTable on the client.

 Here is what you need to do

1. Create SchemaImporterExtension that will recognize the DataSetSchema:

The V2 Framework uses anonymous complexType for DataSet schema:

<s:complexType>
    <s:sequence>
      <s:any minOccurs="0" maxOccurs="unbounded" namespace="http://www.w3.org/2001/XMLSchema" processContents="lax" />
      <s:any minOccurs="1" namespace="urn:schemas-microsoft-com:xml-diffgram-v1" processContents="lax" />
    </s:sequence>
</s:complexType>

You need to write the extension that maps the above schema pattern to a DataTable type:

class DataTableSchemaImporterExtension : SchemaImporterExtension
{
    // DataTableSchemaImporterExtension is used for WebServices, it is used to recognize the schema for DataTable within wsdl
    Hashtable importedTypes = new Hashtable();

    public override string ImportSchemaType(string name, string schemaNamespace, XmlSchemaObject context, XmlSchemas schemas, XmlSchemaImporter importer, CodeCompileUnit compileUnit, CodeNamespace mainNamespace, CodeGenerationOptions options, CodeDomProvider codeProvider)
    {
        IList values = schemas.GetSchemas(schemaNamespace);
        if (values.Count != 1)
        {
            return null;
        }
        XmlSchema schema = values[0] as XmlSchema;
        if (schema == null)
            return null;
        XmlSchemaType type = (XmlSchemaType)schema.SchemaTypes[new XmlQualifiedName(name, schemaNamespace)];
        return ImportSchemaType(type, context, schemas, importer, compileUnit, mainNamespace, options, codeProvider);
    }

    public override string ImportSchemaType(XmlSchemaType type, XmlSchemaObject context, XmlSchemas schemas, XmlSchemaImporter importer, CodeCompileUnit compileUnit, CodeNamespace mainNamespace, CodeGenerationOptions options, CodeDomProvider codeProvider)
    {
        if (type == null)
        {
            return null;
        }
        if (importedTypes[type] != null)
        {
            mainNamespace.Imports.Add(new CodeNamespaceImport(typeof(DataSet).Namespace));
           compileUnit.ReferencedAssemblies.Add("System.Data.dll");
            return (string)importedTypes[type];
        }
        if (!(context is XmlSchemaElement))
            return null;
        if (type is XmlSchemaComplexType)
        {
            XmlSchemaComplexType ct = (XmlSchemaComplexType)type;
            if (ct.Particle is XmlSchemaSequence)
            {
                XmlSchemaObjectCollection items = ((XmlSchemaSequence)ct.Particle).Items;
                if (items.Count == 2 && items[0] is XmlSchemaAny && items[1] is XmlSchemaAny)
                {
                    XmlSchemaAny any0 = (XmlSchemaAny)items[0];
                    XmlSchemaAny any1 = (XmlSchemaAny)items[1];
                    if (any0.Namespace == XmlSchema.Namespace && any1.Namespace == "urn:schemas-microsoft-com:xml-diffgram-v1")
                    {
                        string typeName = typeof(DataTable).FullName;
                        importedTypes.Add(type, typeName);
                      mainNamespace.Imports.Add(new CodeNamespaceImport(typeof(DataTable).Namespace));
           compileUnit.ReferencedAssemblies.Add("System.Data.dll");
                        return typeName;
                    }
                }
            }
        }
        return null;
    }
}

2. Compile and GAC the SchemaImporterExtension
3. Add it to the existent extensions in machine.config, ysing fully-qualified assembly name
   <system.xml.serialization>
      <schemaImporterExtensions>
           <add name="DataTableSchemaImporterExtension" type="DataTableSchemaImporterExtension,        </schemaImporterExtensions>
   </system.xml.serialization>
   

    真麻煩，我還是喜歡用WriteXML()和ReadXml()方法來處理:)