We will be building a web service called PubsWS to let consumers get information from the sample Pubs database. All data access will be done through ADO.NET, so make sure you’ve read Chapter 5 before attempting the examples.

Creating a web service is a three-step process.

The following C# code demonstrates a simple web service that exposes four methods to Internet clients. We emphasize “Internet” because anyone that can access this asmx file on the web server can access these methods, as opposed to your COM component, which can be accessed only by COM clients:

<%@ WebService Language="C#" Class="PubsWS.PubsWS" %>

namespace PubsWS
{
  using System;
  using System.Data;
  using System.Data.OleDb;
  using System.Web;
  using System.Web.Services;

  [WebService(Namespace="http://Oreilly/DotNetEssentials/")]
  public class PubsWS : WebService
  {
    private static string m_sConnStr =
        "provider=sqloledb;server=(local);database=pubs;uid=sa;pwd=;";
[WebMethod(Description="Returns a DataSet containing all authors.")]
    public DataSet GetAuthors(  )
    {
      OleDbDataAdapter oDBAdapter;
      DataSet oDS;

      oDBAdapter = new OleDbDataAdapter("select * from authors", 
                                        m_sConnStr);
      oDS = new DataSet(  );
      oDBAdapter.Fill(oDS, "Authors");
      return oDS;
    }
[WebMethod]
    public DataSet GetAuthor(string sSSN)
    {
      OleDbDataAdapter oDBAdapter;
      DataSet oDS;

      oDBAdapter = new OleDbDataAdapter(
                   "select * from authors where au_id ='"
                   + sSSN + "'", m_sConnStr);
      oDS = new DataSet(  );
      oDBAdapter.Fill(oDS, "SelectedAuthor");
      return oDS;
    }
    [WebMethod(MessageName="GetBooksByAuthor",
               Description="Find books by author's SSN.")]
    public DataSet GetBooks(string sAuthorSSN) 
    {
      OleDbDataAdapter oDBAdapter;
      DataSet oDS;

      oDBAdapter = new OleDbDataAdapter(
                      "select * from titles inner join titleauthor on " +
                      "titles.title_id=titleauthor.title_id " +
                      "where au_id='" + sAuthorSSN + "'", m_sConnStr);
      oDS = new DataSet(  );
      oDBAdapter.Fill(oDS, "Books");
      oDBAdapter = new OleDbDataAdapter("select * from authors " +
                      "where au_id='" + sAuthorSSN + "'", m_sConnStr);
      oDBAdapter.Fill(oDS, "Author");

      return oDS;
    }
[WebMethod]
    public DataSet GetBooks(  ) 
    {
      OleDbDataAdapter oDBAdapter;
      DataSet oDS;

      oDBAdapter = new OleDbDataAdapter("select * from titles" ,
                                        m_sConnStr);
      oDS = new DataSet(  );
      oDBAdapter.Fill(oDS, "Books");
      return oDS;
    }

  } // end PubsWS
}

If you are familiar with ASP, you may recognize the usage of the @ symbol in front of keyword WebService. This WebService directive specifies the language of the web service so that ASP.NET can compile the web service with the correct compiler. This directive also specifies the class that implements the web service so it can load the correct class and employ reflection to generate the WSDL for the web service.

Because PubsWS also uses ADO.NET’s OLE DB provider for its data-access needs, we have to add a reference to System.Data and System.Data.OleDb, in addition to the System, System.Web, and System.Web.Services namespaces.

Class PubsWS inherits from WebService with the colon syntax that should be familiar to C++ or C# developers:

public class PubsWS : WebService

The four methods that are tagged with WebMethod attributes are GetAuthors( ), GetAuthor( ), GetBooks( string), and GetBooks( ). In C#, you can tag public methods with a WebMethod attribute using the [] syntax. In VB, you must use <>. For example, in VB, the second method would be declared as:

Public Function <WebMethod(  )> GetAuthor(sSSN As String) As DataSet

By adding [WebMethod] in front of your public method, you make the public method callable from any Internet client. What goes on behind the scenes is that your public method is associated with an attribute, which is implemented as a WebMethodAttribute class. WebMethodAttribute has six properties:

To set up these properties, pass the property name and its value as a name = value pair:

[WebMethod(Description="Returns a DataSet containing all authors.")]
 public DataSet GetAuthors(  )

You can separate multiple properties with a comma:

[WebMethod(MessageName="GetBooksByAuthor",
            Description="Find books by author's SSN.")]
 public DataSet GetBooks(string sAuthorSSN)

<configuration>
  <system.web>
    <authentication mode="None" />
  </system.web>
</configuration>