HOW TO：專案資料服務查詢結果 (Silverlight 用戶端)
投影在 Open Data Protocol (OData) 中定義為一種方式，可藉由指定回應中僅傳回特定實體屬性的方式來減少查詢傳回的資料量。如此可讓您將資料服務中實體類型的資料投影為用戶端的不同實體類型。 您可以使用 select 子句 (Visual Basic 中則是使用 Select) 執行 LINQ 查詢結果的投影。您也可以呼叫 AddQueryOption 方法將 $select 子句加入至查詢 URI。 如需詳細資訊，請參閱查詢資料服務 (WCF Data Services)。
當您完成 WCF Data Services 快速入門時，便會建立應用程式所存取的 Northwind 範例資料服務。 您也可以使用在 OData 網站上發行的公用 Northwind 範例資料服務；此範例資料服務是唯讀的，因此嘗試儲存變更時會傳回錯誤。
範例
下列範例會顯示一個 LINQ 查詢，此查詢會將 Customer 實體投影至用戶端應用程式中已定義的 CustomerAddress 類型。 CustomerAddress 類別已在用戶端定義並屬性化，如此用戶端程式庫便能將它辨認為實體類型。 這個新類型只包含位址特有的屬性，加上識別屬性。
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));
}
}
);
}
}
}
以下範例顯示上一個範例所使用之 CustomerAddress 類型的定義。
[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
}
下列 XAML 會定義 Silverlight 應用程式的主頁面。
<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>