Web服务返回Dataset对象

using System;
using System.Web.Configuration;
using System.Web.Services;
using System.Data;
using System.Data.SqlClient;
using System.Diagnostics;

/// <summary>
/// Summary description for CategoryService
/// </summary>
[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
// To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line.
// [System.Web.Script.Services.ScriptService]
public class CategoryService : System.Web.Services.WebService {

    public CategoryService () {

        //Uncomment the following line if using designed components
        //InitializeComponent();
    }

    [WebMethod]
    public DataSet GetCategoriesAsDataset()
    {
        try
        {
            using (SqlConnection conn=new SqlConnection())
            {
                string connectionString = WebConfigurationManager.ConnectionStrings["AdventureWorks"].ConnectionString;
                conn.ConnectionString = connectionString;
                SqlCommand command = new SqlCommand("select * from Production.ProductCategory", conn);
                command.CommandType = CommandType.Text;
                SqlDataAdapter adapter = new SqlDataAdapter(command);
                DataSet categories = new DataSet("Categories");
                adapter.Fill(categories);
                return categories;
            }
        }
        catch(Exception ex)
        {
            EventLog.WriteEntry("Application", ex.Message);
            throw ex;
        }
    }

}