Writing your own XSD.exe

If you spend any time working with Web Services or even just XML, you'll inevitably come into contact with XSD.exe and WSDL.exe, they both generate .net code from XSD type definitions. With XSD.exe, you simply give it the path to an xsd document and it will spit out a .cs file. That file defines types that will serialize to an XML document instance that validates against the xsd. De-serializing your XML to a strongly typed object model is almost always better than fiddling with the XML DOM, but what if you don't like the code that XSD.exe generates? Well, you can easily spin your own XSD.exe since it simply uses the public framework types System.Xml.Serialization.XmlSchemaImporter, System.Xml.Serialization.XmlCodeExporter and CodeDom. For some reason the MSDN documentation on these classes says, "This class supports the .NET Framework infrastructure and is not intended to be used directly from your code.", but don't let that put you off, they're public types and work fine. At a high level the process goes like this, you can follow it with the code sample below:

1. Load your xsd file into an XmlSchema.
2. Create an XmlSchemaImporter instance that references your schema. This class is used to generate mappings from XSD types to .net types.
3. Create a CodeDom CodeNamespace instance where you'll build the syntactic structure of your .net types.
4. Create an XmlCodeExporter instance with a reference to the CodeNamespace that you use to export your type. This is the class that actually creates the syntactic structure of the .net types in the CodeNamespace.
5. Create an XmlTypeMapping instance for each type that you wish to export from the XSD.
6. Call the ExportTypeMapping method on XmlCodeExporter for each XmlTypeMapping object, this creates the types syntax in the CodeNamespace object.
7. Use a CSharpCodeProvider to output C# source code for the types that were created in CodeNamespace object.

Once the CodeNamespace has been fully populated (after step 6 above) there's an opportunity to make any changes that we wish to the code we output. Note that at this stage, the CodeDom CodeNamespace object represents an IL syntactic structure rather than code in a particular language. We could just as easily generate VB.NET at this point. We can use the CodeDom methods to alter that structure before outputting source code. In the example below I run the RemoveAttributes function to remove some attributes from the type definition.

using System;
using System.IO;
using System.Collections.Generic;
using System.Reflection;
using System.Text;
using System.Xml;
using System.Xml.Serialization;
using System.Xml.Schema;
using System.CodeDom;
using System.CodeDom.Compiler;

using Microsoft.CSharp;

using NUnit.Framework;

namespace XmlSchemaImporterTest
{
  [TestFixture]
  public class XsdToClassTests
  {
      // Test for XmlSchemaImporter
      [Test]
      public void XsdToClassTest()
      {
          // identify the path to the xsd
          string xsdFileName = "Account.xsd";
          string path = Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location);
          string xsdPath = Path.Combine(path, xsdFileName);

          // load the xsd
          XmlSchema xsd;
          using(FileStream stream = new FileStream(xsdPath, FileMode.Open, FileAccess.Read))
          {
              xsd = XmlSchema.Read(stream, null);
          }
          Console.WriteLine("xsd.IsCompiled {0}", xsd.IsCompiled);

          XmlSchemas xsds = new XmlSchemas();
          xsds.Add(xsd);
          xsds.Compile(null, true);
          XmlSchemaImporter schemaImporter = new XmlSchemaImporter(xsds);

          // create the codedom
          CodeNamespace codeNamespace = new CodeNamespace("Generated");
          XmlCodeExporter codeExporter = new XmlCodeExporter(codeNamespace);

          List maps = new List();
          foreach(XmlSchemaType schemaType in xsd.SchemaTypes.Values)
          {
              maps.Add(schemaImporter.ImportSchemaType(schemaType.QualifiedName));
          }
          foreach(XmlSchemaElement schemaElement in xsd.Elements.Values)
          {
              maps.Add(schemaImporter.ImportTypeMapping(schemaElement.QualifiedName));
          }
          foreach(XmlTypeMapping map in maps)
          {
              codeExporter.ExportTypeMapping(map);
          }

          RemoveAttributes(codeNamespace);

          // Check for invalid characters in identifiers
          CodeGenerator.ValidateIdentifiers(codeNamespace);

          // output the C# code
          CSharpCodeProvider codeProvider = new CSharpCodeProvider();

          using(StringWriter writer = new StringWriter())
          {
              codeProvider.GenerateCodeFromNamespace(codeNamespace, writer, new CodeGeneratorOptions());
              Console.WriteLine(writer.GetStringBuilder().ToString());
          }

          Console.ReadLine();
      }

      // Remove all the attributes from each type in the CodeNamespace, except
      // System.Xml.Serialization.XmlTypeAttribute
      private void RemoveAttributes(CodeNamespace codeNamespace)
      {
          foreach(CodeTypeDeclaration codeType in codeNamespace.Types)
          {
              CodeAttributeDeclaration xmlTypeAttribute = null;
              foreach(CodeAttributeDeclaration codeAttribute in codeType.CustomAttributes)
              {
                  Console.WriteLine(codeAttribute.Name);
                  if(codeAttribute.Name == "System.Xml.Serialization.XmlTypeAttribute")
                  {
                      xmlTypeAttribute = codeAttribute;
                  }
              }
              codeType.CustomAttributes.Clear();
              if(xmlTypeAttribute != null)
              {
                  codeType.CustomAttributes.Add(xmlTypeAttribute);
              }
          }
      }
  }
}