Cómo: Proyectar los resultados de una consulta de servicio de datos (Cliente de Silverlight)

La proyección se define en el Open Data Protocol (OData) como una forma de reducir la cantidad de datos devueltos por una consulta especificando que solo se devuelvan determinadas propiedades de una entidad en la respuesta. Esto le permite proyectar los datos de un tipo de entidad del servicio de datos en un tipo de entidad diferente en el cliente. Puede realizar proyecciones en los resultados de una consulta LINQ si usa la cláusula select (Select en Visual Basic). También puede llamar al método AddQueryOption para agregar una cláusula $select al URI de consulta. Para obtener más información, vea Consultar el servicio de datos (WCF Data Services).

Cuando complete el tutorial rápido de Servicios de datos de Microsoft WCF se creará el servicio de datos de ejemplo Northwind al que tiene acceso la aplicación. También puede usar el servicio de datos de ejemplo Northwind público que está en el sitio web de OData; este servicio de datos de ejemplo es de solo lectura y si se intentan guardar los cambios, devuelve un error.

Ejemplo

En el ejemplo siguiente se muestra una consulta LINQ que proyecta entidades Customer en el tipo CustomerAddress que ya se ha definido en la aplicación cliente. La clase CustomerAddress se define en el cliente y recibe el atributo para que la biblioteca cliente pueda reconocerla como tipo de entidad. Este nuevo tipo solo contiene propiedades específicas de la dirección, así como la propiedad de identidad.

Imports System
Imports System.Linq
Imports System.Windows
Imports System.Windows.Controls
Imports System.Windows.Data
Imports ClientProjection.Northwind
Imports System.Data.Services.Client

Partial Public Class MainPage
    Inherits UserControl

    ' Create the binding collections and the data service context.
    Dim binding As DataServiceCollection(Of CustomerAddress)
    Dim context As NorthwindEntities
    Dim customerAddressViewSource As CollectionViewSource

    Public Sub Main()
        InitializeComponent()
    End Sub

    Private Sub MainPage_Loaded(ByVal sender As Object, ByVal e As RoutedEventArgs)
        'Instantiate the binding collection.
        binding = New DataServiceCollection(Of CustomerAddress)()

        ' Instantiate the context.
        context = _
            New NorthwindEntities(New Uri("https://localhost:54321/Northwind.svc/"))

        ' Define a handler for the LoadCompleted event of the collection.
        AddHandler binding.LoadCompleted, _
        AddressOf binding_LoadCompleted

        ' Define an anonymous LINQ query that projects the Customers type into 
        ' a CustomerAddress type that contains only address properties.
        Dim query = From c In context.Customers _
                            Where c.Country = "Germany" _
                            Select New CustomerAddress With
                                {.CustomerID = c.CustomerID, _
                                 .Address = c.Address, _
                                 .City = c.City, _
                                 .PostalCode = c.PostalCode, _
                                 .Country = c.Country _
                                }

        ' Execute the query asynchronously.
        binding.LoadAsync(query)
    End Sub

    Private Sub binding_LoadCompleted(ByVal sender As Object, ByVal e As LoadCompletedEventArgs)
        If e.Error Is Nothing Then
            ' Load all pages of Customers before binding.
            If Not binding.Continuation Is Nothing Then
                binding.LoadNextPartialSetAsync()
            Else
                ' Load your data here and assign the result to the CollectionViewSource.
                customerAddressViewSource =
                    CType(Me.Resources("customerAddressViewSource"), CollectionViewSource)
                customerAddressViewSource.Source = binding
            End If
        End If
    End Sub
    ' We need to persist the result of an operation 
    ' to be able to invoke the dispatcher.
    Private currentResult As IAsyncResult
    Private Sub saveChangesButton_Click(ByVal sender As Object, ByVal e As RoutedEventArgs)
        ' Define the delegate to callback into the process
        Dim callback As AsyncCallback = AddressOf OnChangesSaved
        Try
            ' Start the saving changes operation. This needs to be a 
            ' batch operation in case we are added a new object with 
            ' a new relationship.
            context.BeginSaveChanges(SaveChangesOptions.Batch, _
                    callback, context)

        Catch ex As Exception
            MessageBox.Show(String.Format( _
                            "The changes could not be saved to the data service.\n" _
                            & "The following error occurred: {0}", ex.Message))
        End Try
    End Sub
    Private Sub OnChangesSaved(ByVal result As IAsyncResult)
        ' Persist the result for the delegate.
        currentResult = result

        ' Use the Dispatcher to ensure that the 
        ' asynchronous call returns in the correct thread.
        Dispatcher.BeginInvoke(AddressOf ChangesSavedByDispatcher)
    End Sub
    Private Sub ChangesSavedByDispatcher()

        Dim errorOccured As Boolean = False
        context = CType(currentResult.AsyncState, NorthwindEntities)

        Try
            ' Complete the save changes operation and display the response.
            Dim response As DataServiceResponse = _
            context.EndSaveChanges(currentResult)

            For Each changeResponse As ChangeOperationResponse In response
                If changeResponse.Error IsNot Nothing Then errorOccured = True
            Next
            If Not errorOccured Then
                MessageBox.Show("The changes have been saved to the data service.")
            Else
                MessageBox.Show("An error occured. One or more changes could not be saved.")
            End If
        Catch ex As Exception
            ' Display the error from the response.
            MessageBox.Show(String.Format("The following error occured: {0}", ex.Message))
        End Try
    End Sub
End Class

using System;
using System.Linq;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using ClientProjection.Northwind;
using System.Data.Services.Client;

namespace ClientProjection
{
    public partial class MainPage : UserControl
    {
        // Create the binding collections and the data service context.
        private DataServiceCollection<CustomerAddress> binding;
        NorthwindEntities context;
        CollectionViewSource customerAddressViewSource;

        public MainPage()
        {
            InitializeComponent();
        }

        private void MainPage_Loaded(object sender, RoutedEventArgs e)
        {
            // Instantiate the binding collection.
            binding = new DataServiceCollection<CustomerAddress>();

            // Instantiate the context.
            context = 
                new NorthwindEntities(new Uri("https://localhost:12345/Northwind.svc/"));

            // Register the LoadCompleted event for the binding collection.
            binding.LoadCompleted += new EventHandler<LoadCompletedEventArgs>(binding_LoadCompleted);

            // Define an anonymous LINQ query that projects the Customers type into 
            // a CustomerAddress type that contains only address properties.
            var query = from c in context.Customers
                        where c.Country == "Germany"
                        select new CustomerAddress
                        {
                            CustomerID = c.CustomerID,
                            Address = c.Address,
                            City = c.City,
                            PostalCode = c.PostalCode,
                            Country = c.Country
                        };

            // Execute the query asynchronously.
            binding.LoadAsync(query);
        }

        void binding_LoadCompleted(object sender, LoadCompletedEventArgs e)
        {
            if (e.Error == null)
            {
                // Load all pages of Customers before binding.
                if (binding.Continuation != null)
                {
                    binding.LoadNextPartialSetAsync();
                }
                else
                {
                    //Load your data here and assign the result to the CollectionViewSource.

                    customerAddressViewSource = 
                        (CollectionViewSource)this.Resources["customerAddressViewSource"];
                    customerAddressViewSource.Source = binding;
                }
            }
        }
        private void saveChangesButton_Click(object sender, RoutedEventArgs e)
        {
            try
            {
                // Start the saving changes operation. 
                context.BeginSaveChanges(OnChangesSaved, context);
            }
            catch (Exception ex)
            {
                MessageBox.Show(string.Format("The changes could not be saved to the data service.\n"
                    + "The following error occurred: {0}", ex.Message));
            }
        }

        private void OnChangesSaved(IAsyncResult result)
        {
            bool errorOccured = false;

            // Use the Dispatcher to ensure that the 
            // asynchronous call returns in the correct thread.
            Dispatcher.BeginInvoke(() =>
            {
                context = result.AsyncState as NorthwindEntities;

                try
                {
                    // Complete the save changes operation and display the response.
                    DataServiceResponse response = context.EndSaveChanges(result);

                    foreach (ChangeOperationResponse changeResponse in response)
                    {
                        if (changeResponse.Error != null) errorOccured = true;
                    }
                    if (!errorOccured)
                    {
                        MessageBox.Show("The changes have been saved to the data service.");
                    }
                    else
                    {
                        MessageBox.Show("An error occured. One or more changes could not be saved.");
                    }
                }
                catch (Exception ex)
                {
                    // Display the error from the response.
                    MessageBox.Show(string.Format("The following error occured: {0}", ex.Message));
                }
            }
            );
        }
    }
}

En el ejemplo siguiente se muestra la definición del tipo CustomerAddress usado en el ejemplo anterior.

[DataServiceKey("CustomerID")]
public partial class CustomerAddress : INotifyPropertyChanged
{
    private string _customerID;
    private string _address;
    private string _city;
    private string _postalCode;
    private string _country;

    public string CustomerID
    {
        get { return this._customerID; }
        set
        {
            this.OnCustomerIDChanging(value);
            this._customerID = value;
            this.OnCustomerIDChanged();
            this.OnPropertyChanged("CustomerID");
        }
    }
    public string Address
    {
        get { return this._address; }
        set
        {
            this.OnAddressChanging(value);
            this._address = value;
            this.OnAddressChanged();
            this.OnPropertyChanged("Address");
        }
    }
    public string City
    {
        get { return this._city; }
        set
        {
            this.OnCityChanging(value);
            this._city = value;
            this.OnCityChanged();
            this.OnPropertyChanged("City");
        }
    }
    public string PostalCode
    {
        get { return this._postalCode; }
        set
        {
            this.OnPostalCodeChanging(value);
            this._postalCode = value;
            this.OnPostalCodeChanged();
            this.OnPropertyChanged("PostalCode");
        }
    }
    public string Country
    {
        get { return this._country; }
        set
        {
            this.OnCountryChanging(value);
            this._country = value;
            this.OnCountryChanged();
            this.OnPropertyChanged("Country");
        }
    }
    #region INotifyPropertyChanged implementation
    // Members required by the INotifyPropertyChanged implementation.
    public event PropertyChangedEventHandler PropertyChanged;
    protected virtual void OnPropertyChanged(string property)
    {
        if ((this.PropertyChanged != null))
        {
            this.PropertyChanged(this, new PropertyChangedEventArgs(property));
        }
    }
    partial void OnCustomerIDChanging(string value);
    partial void OnCustomerIDChanged();
    partial void OnAddressChanging(string value);
    partial void OnAddressChanged();
    partial void OnCityChanging(string value);
    partial void OnCityChanged();
    partial void OnRegionChanging(string value);
    partial void OnRegionChanged();
    partial void OnPostalCodeChanging(string value);
    partial void OnPostalCodeChanged();
    partial void OnCountryChanging(string value);
    partial void OnCountryChanged();
    #endregion
}

El código XAML siguiente define la página principal de la aplicación de Silverlight.

    <UserControl x:Class="ClientProjection.MainPage"
    xmlns="https://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="https://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="https://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="https://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    d:DesignHeight="312" d:DesignWidth="577" 
             xmlns:sdk="https://schemas.microsoft.com/winfx/2006/xaml/presentation/sdk" 
             xmlns:my="clr-namespace:ClientProjection" Loaded="MainPage_Loaded">
    <UserControl.Resources>
        <CollectionViewSource x:Key="customerAddressViewSource" 
                              d:DesignSource="{d:DesignInstance my:CustomerAddress, CreateList=True}" />
    </UserControl.Resources>
    <Grid x:Name="LayoutRoot" Background="White" DataContext="" Height="312" Width="577"
          VerticalAlignment="Top" HorizontalAlignment="Left">
        <Grid.RowDefinitions>
            <RowDefinition Height="203*" />
            <RowDefinition Height="119*" />
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="17*" />
            <ColumnDefinition Width="336*" />
        </Grid.ColumnDefinitions>
        <sdk:DataGrid AutoGenerateColumns="False" Height="233" HorizontalAlignment="Left" 
                      ItemsSource="{Binding Source={StaticResource customerAddressViewSource}}" 
                      Name="customerAddressDataGrid" RowDetailsVisibilityMode="VisibleWhenSelected" 
                      VerticalAlignment="Top" Width="553" Margin="12,24,0,0" 
                      Grid.RowSpan="2" Grid.ColumnSpan="2">
            <sdk:DataGrid.Columns>
                <sdk:DataGridTextColumn x:Name="customerIDColumn" Binding="{Binding Path=CustomerID}" 
                                        Header="Customer" Width="80" />
                <sdk:DataGridTextColumn x:Name="addressColumn" Binding="{Binding Path=Address}" 
                                        Header="Address" Width="180" />
                <sdk:DataGridTextColumn x:Name="cityColumn" Binding="{Binding Path=City}" 
                                        Header="City" Width="120" />
                <sdk:DataGridTextColumn x:Name="countryColumn" Binding="{Binding Path=Country}" 
                                        Header="Country" Width="80" />
                <sdk:DataGridTextColumn x:Name="postalCodeColumn" Binding="{Binding Path=PostalCode}" 
                                        Header="Postal Code" Width="90" />
            </sdk:DataGrid.Columns>
        </sdk:DataGrid>
        <Button Content="Save" Grid.Column="1" HorizontalAlignment="Left" 
                Margin="462,78,0,0" Name="saveChangesButton" Width="75" Grid.Row="1" 
                Click="saveChangesButton_Click" Height="25" VerticalAlignment="Top" />
    </Grid>
</UserControl>

Vea también

Otros recursos

WCF Data Services Tasks for Silverlight