Strongly Typed .NET DataSet

We learned about two different approaches to access XML data: transforming each element in an XML document into a .NET object with the XmlSerializer or loading entire XML documents into an ADO.NET DataSet. We can access and manipulate the data in the DataSet through tables, rows and columns, just as if we were accessing a database. Chapter 8 also introduced us to typed DataSets that enforce a specific structure on the XML data they expose.

It is rather complex to create a typed DataSet class by hand. Fortunately the schema definition tool can create a typed DataSet from an XSD schema that describes the data structure. We simply need to let the tool know to produce a DataSet class rather than a class for the XmlSerializer when we specify a file with a .xsd extension by replacing the /d with the /d option. The following example creates a DataSet from the schema in listing C.2:

xsd.exe garage.xsd /d

Elements in the schema are modeled as tables; relationships between the elements are expressed as relationships between these tables as following code snippet shows:

8           Listing C.8 Types DataSet definition created by the XSD tool.

using System;

using System.Data;

using System.Xml;

using System.Runtime.Serialization;

[Serializable()]

[System.ComponentModel.DesignerCategoryAttribute("code")]

[System.Diagnostics.DebuggerStepThrough()]

[System.ComponentModel.ToolboxItem(true)]

public class NewDataSet : DataSet {             | #1

  private garageDataTable tablegarage;        | #2

  private carDataTable tablecar;              |

  private garageCarDataTable tablegarageCar;  |

  private DataRelation relationgarage_car;    |

  public NewDataSet() {

      this.InitClass();

      System.ComponentModel.CollectionChangeEventHandler

        schemaChangedHandler = new

          System.ComponentModel.CollectionChangeEventHandler(

            this.SchemaChanged);

      this.Tables.CollectionChanged += schemaChangedHandler;

      this.Relations.CollectionChanged += schemaChangedHandler;

  }

  protected NewDataSet(SerializationInfo info,

    StreamingContext context) {

    string strSchema = ((string)(info.GetValue("XmlSchema",

      typeof(string))));

    if ((strSchema != null)) {

      DataSet ds = new DataSet();

      ds.ReadXmlSchema(new XmlTextReader(

        new System.IO.StringReader(strSchema)));

      if ((ds.Tables["garage"] != null)) {

        this.Tables.Add(new garageDataTable(ds.Tables["garage"]));

      …(annotation) <#1 The schema id is used for the class name. The class derives from the DataSet class/ >

(annotation) <#1 Elements in the schema are represented as tables and relationships.>

The listing for the complete class would go on for the next fifteen or so pages, but I think you get the point: Creating a typed DataSet and all supporting classes is very complex. The XSD tool is the only viable option to create typed DataSet classes.

XSD Switches

We can mix the /l and /n options together with the /d option to select the programming language and the .NET namespace. The /e and /u option however, have no effect on the generated DataSet.