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Consuming a DataSet from an XML Web Service 

The DataSet was architected with a disconnected design, in part to facilitate the convenient transport of data over the Internet. The DataSet is "serializable" in that it can be specified as an input to or output from XML Web services without any additional coding required to stream the contents of the DataSet from an XML Web service to a client and back. The DataSet is implicitly converted to an XML stream using the DiffGram format, sent over the network, and then reconstructed from the XML stream as a DataSet on the receiving end. This gives you a very simple and flexible method for transmitting and returning relational data using XML Web services. For more information about the DiffGram format, see DiffGrams.

The following example shows how to create an XML Web service and client that use the DataSet to transport relational data (including modified data) and resolve any updates back to the original data source.

NoteNote

We recommend that you always consider security implications when creating an XML Web service. For information on securing an XML Web service, see Securing XML Web Services Created Using ASP.NET.

To create an XML Web service that returns and consumes a DataSet

  1. Create the XML Web service.

    In the example, an XML Web service is created that returns data, in this case a list of customers from the Northwind database, and receives a DataSet with updates to the data, which the XML Web service resolves back to the original data source.

    The XML Web service exposes two methods: GetCustomers, to return the list of customers, and UpdateCustomers, to resolve updates back to the data source. The XML Web service is stored in a file on the Web server called DataSetSample.asmx. The following code outlines the contents of DataSetSample.asmx.

    <% @ WebService Language = "vb" Class = "Sample" %>
    Imports System
    Imports System.Data
    Imports System.Data.SqlClient
    Imports System.Web.Services
    
    <WebService(Namespace:="http://microsoft.com/webservices/")> _
    Public Class Sample
    
    Public connection As SqlConnection = New SqlConnection("Data Source=(local);Integrated Security=SSPI;Initial Catalog=Northwind")
    
      <WebMethod( Description := "Returns Northwind Customers", EnableSession := False )> _
      Public Function GetCustomers() As DataSet
        Dim adapter As SqlDataAdapter = New SqlDataAdapter( _
          "SELECT CustomerID, CompanyName FROM Customers", connection)
    
        Dim custDS As DataSet = New DataSet()
        adapter.MissingSchemaAction = MissingSchemaAction.AddWithKey
        adapter.Fill(custDS, "Customers")
    
        Return custDS
      End Function
    
      <WebMethod( Description := "Updates Northwind Customers", EnableSession := False )> _
      Public Function UpdateCustomers(custDS As DataSet) As DataSet
        Dim adapter As SqlDataAdapter = New SqlDataAdapter()
    
        adapter.InsertCommand = New SqlCommand( _
          "INSERT INTO Customers (CustomerID, CompanyName) " & _
          "Values(@CustomerID, @CompanyName)", connection)
        adapter.InsertCommand.Parameters.Add( _
          "@CustomerID", SqlDbType.NChar, 5, "CustomerID")
        adapter.InsertCommand.Parameters.Add( _
          "@CompanyName", SqlDbType.NChar, 15, "CompanyName")
    
        adapter.UpdateCommand = New SqlCommand( _
          "UPDATE Customers Set CustomerID = @CustomerID, " & _
          "CompanyName = @CompanyName WHERE CustomerID = " & _
          @OldCustomerID", connection)
        adapter.UpdateCommand.Parameters.Add( _
          "@CustomerID", SqlDbType.NChar, 5, "CustomerID")
        adapter.UpdateCommand.Parameters.Add( _
          "@CompanyName", SqlDbType.NChar, 15, "CompanyName")
    
        Dim parameter As SqlParameter = _
          adapter.UpdateCommand.Parameters.Add( _
          "@OldCustomerID", SqlDbType.NChar, 5, "CustomerID")
        parameter.SourceVersion = DataRowVersion.Original
    
        adapter.DeleteCommand = New SqlCommand( _
          "DELETE FROM Customers WHERE CustomerID = @CustomerID", _
          connection)
        parameter = adapter.DeleteCommand.Parameters.Add( _
          "@CustomerID", SqlDbType.NChar, 5, "CustomerID")
        parameter.SourceVersion = DataRowVersion.Original
    
        adapter.Update(custDS, "Customers")
    
        Return custDS
      End Function
    End Class
    
    

    <% @ WebService Language = "C#" Class = "Sample" %>
    using System;
    using System.Data;
    using System.Data.SqlClient;
    using System.Web.Services;
    
    [WebService(Namespace="http://microsoft.com/webservices/")]
    public class Sample
    {
      public SqlConnection connection = new SqlConnection("Data Source=(local);Integrated Security=SSPI;Initial Catalog=Northwind");
    
      [WebMethod( Description = "Returns Northwind Customers", EnableSession = false )]
      public DataSet GetCustomers()
      {
        SqlDataAdapter adapter = new SqlDataAdapter(
          "SELECT CustomerID, CompanyName FROM Customers", connection);
    
        DataSet custDS = new DataSet();
        adapter.MissingSchemaAction = MissingSchemaAction.AddWithKey;
        adapter.Fill(custDS, "Customers");
     
        return custDS;
      }
    
      [WebMethod( Description = "Updates Northwind Customers",
        EnableSession = false )]
      public DataSet UpdateCustomers(DataSet custDS)
      {
        SqlDataAdapter adapter = new SqlDataAdapter();
    
        adapter.InsertCommand = new SqlCommand(
          "INSERT INTO Customers (CustomerID, CompanyName) " +
          "Values(@CustomerID, @CompanyName)", connection);
        adapter.InsertCommand.Parameters.Add(
          "@CustomerID", SqlDbType.NChar, 5, "CustomerID");
        adapter.InsertCommand.Parameters.Add(
          "@CompanyName", SqlDbType.NChar, 15, "CompanyName");
    
        adapter.UpdateCommand = new SqlCommand(
          "UPDATE Customers Set CustomerID = @CustomerID, " +
          "CompanyName = @CompanyName WHERE CustomerID = " +
          "@OldCustomerID", connection);
        adapter.UpdateCommand.Parameters.Add(
          "@CustomerID", SqlDbType.NChar, 5, "CustomerID");
        adapter.UpdateCommand.Parameters.Add(
          "@CompanyName", SqlDbType.NChar, 15, "CompanyName");
        SqlParameter parameter = adapter.UpdateCommand.Parameters.Add(
          "@OldCustomerID", SqlDbType.NChar, 5, "CustomerID");
        parameter.SourceVersion = DataRowVersion.Original;
    
        adapter.DeleteCommand = new SqlCommand(
        "DELETE FROM Customers WHERE CustomerID = @CustomerID",
         connection);
        parameter = adapter.DeleteCommand.Parameters.Add(
          "@CustomerID", SqlDbType.NChar, 5, "CustomerID");
        parameter.SourceVersion = DataRowVersion.Original;
    
        adapter.Update(custDS, "Customers");
    
        return custDS;
      }
    }
    

    In a typical scenario, the UpdateCustomers method would be written to catch optimistic concurrency violations. For simplicity, the example does not include this. For more information about optimistic concurrency, see Using Optimistic Concurrency.

  2. Create an XML Web service proxy.

    Clients of the XML Web service require a SOAP proxy in order to consume the exposed methods. You can have Visual Studio generate this proxy for you. By setting a Web reference to an existing Web service from within Visual Studio, all the behavior described in this step occurs transparently. If you want to create the proxy class yourself, continue with this discussion. In most circumstances, however, using Visual Studio to create the proxy class for the client application is sufficient.

    A proxy can be created using the Web Services Description Language Tool. For example, if the XML Web service is exposed at the URL http://myserver/data/DataSetSample.asmx, issue a command such as the following to create a Visual Basic .NET proxy with a namespace of WebData.DSSample and store it in the file sample.vb.

    wsdl /l:VB /out:sample.vb http://myserver/data/DataSetSample.asmx /n:WebData.DSSample
    

    To create a C# proxy in the file sample.cs, issue the following command.

    wsdl /l:CS /out:sample.cs http://myserver/data/DataSetSample.asmx /n:WebData.DSSample
    

    The proxy can then be compiled as a library and imported into the XML Web service client. To compile the Visual Basic .NET proxy code stored in sample.vb as sample.dll, issue the following command.

    vbc /t:library /out:sample.dll sample.vb /r:System.dll /r:System.Web.Services.dll /r:System.Data.dll /r:System.Xml.dll
    

    To compile the C# proxy code stored in sample.cs as sample.dll, issue the following command.

    csc /t:library /out:sample.dll sample.cs /r:System.dll /r:System.Web.Services.dll /r:System.Data.dll /r:System.Xml.dll
    
  3. Create an XML Web service client.

    If you want to have Visual Studio generate the Web service proxy class for you, simply create the client project, and, in the Solution Explorer window, right-click the project, click Add Web Reference, and select the Web service from the list of available Web services (this may require supplying the address of the Web service endpoint, if the Web service isn't available within the current solution, or on the current computer.) If you create the XML Web service proxy yourself (as described in the previous step), you can import it into your client code and consume the XML Web service methods. The following sample code imports the proxy library, calls GetCustomers to get a list of customers, adds a new customer, and then returns a DataSet with the updates to UpdateCustomers.

    Notice that the example passes the DataSet returned by DataSet.GetChanges to UpdateCustomers because only modified rows need to be passed to UpdateCustomers. UpdateCustomers returns the resolved DataSet, which you can then Merge into the existing DataSet to incorporate the resolved changes and any row error information from the update. The following code assumes that you have used Visual Studio to create the Web reference, and that you have renamed the Web reference to DsSample in the Add Web Reference dialog box.

    Imports System
    Imports System.Data
    
    Public Class Client
    
      Public Shared Sub Main()
        Dim proxySample As New DsSample.Sample ()  ' Proxy object.
        Dim customersDataSet As DataSet = proxySample.GetCustomers()
        Dim customersTable As DataTable = _
          customersDataSet.Tables("Customers")
    
        Dim rowAs DataRow = customersTable.NewRow()
        row("CustomerID") = "ABCDE"
        row("CompanyName") = "New Company Name"
        customersTable.Rows.Add(row)
    
        Dim updateDataSet As DataSet = _
          proxySample.UpdateCustomers(customersDataSet.GetChanges())
    
        customersDataSet.Merge(updateDataSet)
        customersDataSet.AcceptChanges()
      End Sub
    End Class
    
    

    using System;
    using System.Data;
    
    public class Client
    {
      public static void Main()
      {
        Sample proxySample = new DsSample.Sample();  // Proxy object.
        DataSet customersDataSet = proxySample.GetCustomers();
        DataTable customersTable = customersDataSet.Tables["Customers"];
    
        DataRow row = customersTable.NewRow();
        row["CustomerID"] = "ABCDE";
        row["CompanyName"] = "New Company Name";
        customersTable.Rows.Add(row);
    
        DataSet updateDataSet = new DataSet();
    
        updateDataSet = 
          proxySample.UpdateCustomers(customersDataSet.GetChanges());
    
        customersDataSet.Merge(updateDataSet);
        customersDataSet.AcceptChanges();
      }
    }
    

    If you decide to create the proxy class yourself, you must take the following extra steps. To compile the sample, supply the proxy library that was created (sample.dll) and the related .NET libraries. To compile the Visual Basic .NET version of the sample, stored in the file client.vb, issue the following command.

    vbc client.vb /r:sample.dll /r:System.dll /r:System.Data.dll /r:System.Xml.dll /r:System.Web.Services.dll
    

    To compile the C# version of the sample, stored in the file client.cs, issue the following command.

    csc client.cs /r:sample.dll /r:System.dll /r:System.Data.dll /r:System.Xml.dll /r:System.Web.Services.dll
    

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