Procedura: proiettare i risultati delle query del servizio dati (client Silverlight)
In OData (Open Data Protocol) la proiezione viene definita come un modo per ridurre la quantità di dati restituiti da una query specificando che solo determinate proprietà di un'entità vengano restituite nella risposta. In questo modo sarà possibile proiettare i dati da un tipo di entità nel servizio dati in un tipo di entità diverso nel client. È possibile eseguire proiezioni sui risultati di una query LINQ mediante la clausola select (Select in Visual Basic). È inoltre possibile chiamare il metodo AddQueryOption per aggiungere una clausola $select all'URI della query. Per ulteriori informazioni, vedere Esecuzione di query sul servizio dati (WCF Data Services).
Al termine della Guida rapida di WCF Data Services verrà creato il servizio dati Northwind di esempio a cui accede l'applicazione. È inoltre possibile utilizzare il servizio dati Northwind di esempio pubblico, disponibile sul sito Web OData. Questo servizio dati di esempio è di sola lettura e viene restituito un errore se si tenta di salvare le modifiche.
Esempio
Nell'esempio seguente viene mostrata una query LINQ che proietta entità Customer nel tipo CustomerAddress già definito nell'applicazione client. La classe CustomerAddress viene definita nel client e attribuita in modo da essere riconosciuta come tipo di entità dalla libreria client. Questo nuovo tipo contiene sono proprietà specifiche dell'indirizzo e la proprietà Identity.
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));
}
}
);
}
}
}
Nell'esempio riportato di seguito viene illustrata la definizione del tipo CustomerAddress utilizzato nell'esempio precedente.
[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
}
Tramite il codice XAML seguente viene definita la pagina principale dell'applicazione 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>