Gewusst wie: Laden von ausgelagerten Ergebnissen (WCF Data Services)
WCF Data Services ermöglicht es dem Datendienst, die Anzahl von Entitäten zu beschränken, die in einem einzelnen Antwortfeed zurückgegeben werden. In diesem Fall enthält der abschließende Eintrag im Feed einen Link zur nächsten Datenseite. Der URI zur nächsten Datenseite wird abgerufen, indem Sie die GetContinuation-Methode der QueryOperationResponse<T> aufrufen, die beim Ausführen der DataServiceQuery<TElement> zurückgegeben wird. Der von diesem Objekt dargestellte URI wird dann verwendet, um die nächste Ergebnisseite zu laden. Weitere Informationen finden Sie unter Laden von verzögertem Inhalt (WCF Data Services).
Im Beispiel in diesem Thema werden der Northwind-Beispieldatendienst und automatisch generierte Clientdatendienstklassen verwendet. Dieser Dienst und die Clientdatenklassen werden erstellt, wenn Sie den WCF Data Services-Schnellstart ausführen.
Beispiel
In diesem Beispiel werden Customers-Entitäten aus ausgelagerten Ergebnissen aus dem Datendienst mithilfe einer do…while-Schleife geladen.
' Create the DataServiceContext using the service URI.
Dim context = New NorthwindEntities(svcUri)
Dim token As DataServiceQueryContinuation(Of Customer) = Nothing
Dim pageCount = 0
Try
' Execute the query for all customers and get the response object.
Dim response As QueryOperationResponse(Of Customer) = _
CType(context.Customers.Execute(), QueryOperationResponse(Of Customer))
' With a paged response from the service, use a do...while loop
' to enumerate the results before getting the next link.
Do
' Write the page number.
Console.WriteLine("Page {0}:", pageCount + 1)
' If nextLink is not null, then there is a new page to load.
If token IsNot Nothing Then
' Load the new page from the next link URI.
response = CType(context.Execute(Of Customer)(token), _
QueryOperationResponse(Of Customer))
End If
' Enumerate the customers in the response.
For Each customer As Customer In response
Console.WriteLine(vbTab & "Customer Name: {0}", customer.CompanyName)
Next
' Get the next link, and continue while there is a next link.
token = response.GetContinuation()
Loop While token IsNot Nothing
Catch ex As DataServiceQueryException
Throw New ApplicationException( _
"An error occurred during query execution.", ex)
End Try
// Create the DataServiceContext using the service URI.
NorthwindEntities context = new NorthwindEntities(svcUri);
DataServiceQueryContinuation<Customer> token = null;
int pageCount = 0;
try
{
// Execute the query for all customers and get the response object.
QueryOperationResponse<Customer> response =
context.Customers.Execute() as QueryOperationResponse<Customer>;
// With a paged response from the service, use a do...while loop
// to enumerate the results before getting the next link.
do
{
// Write the page number.
Console.WriteLine("Page {0}:", pageCount++);
// If nextLink is not null, then there is a new page to load.
if (token != null)
{
// Load the new page from the next link URI.
response = context.Execute<Customer>(token)
as QueryOperationResponse<Customer>;
}
// Enumerate the customers in the response.
foreach (Customer customer in response)
{
Console.WriteLine("\tCustomer Name: {0}", customer.CompanyName);
}
}
// Get the next link, and continue while there is a next link.
while ((token = response.GetContinuation()) != null);
}
catch (DataServiceQueryException ex)
{
throw new ApplicationException(
"An error occurred during query execution.", ex);
}
In diesem Beispiel werden verknüpfte Orders-Entitäten mit jeder Customers-Entität zurückgegeben, und es wird eine do…while-Schleife zum Laden von Customers-Entitätenseiten und eine geschachtelte while-Schleife zum Laden verknüpfter Orders-Entitäten aus dem Datendienst verwendet.
' Create the DataServiceContext using the service URI.
Dim context = New NorthwindEntities(svcUri)
Dim nextLink As DataServiceQueryContinuation(Of Customer) = Nothing
Dim pageCount = 0
Dim innerPageCount = 0
Try
' Execute the query for all customers and related orders,
' and get the response object.
Dim response = _
CType(context.Customers.AddQueryOption("$expand", "Orders") _
.Execute(), QueryOperationResponse(Of Customer))
' With a paged response from the service, use a do...while loop
' to enumerate the results before getting the next link.
Do
' Write the page number.
Console.WriteLine("Customers Page {0}:", ++pageCount)
' If nextLink is not null, then there is a new page to load.
If nextLink IsNot Nothing Then
' Load the new page from the next link URI.
response = CType(context.Execute(Of Customer)(nextLink), _
QueryOperationResponse(Of Customer))
End If
' Enumerate the customers in the response.
For Each c As Customer In response
Console.WriteLine(vbTab & "Customer Name: {0}", c.CompanyName)
Console.WriteLine(vbTab & "Orders Page {0}:", innerPageCount + 1)
' Get the next link for the collection of related Orders.
Dim nextOrdersLink As DataServiceQueryContinuation(Of Order) = _
response.GetContinuation(c.Orders)
While nextOrdersLink IsNot Nothing
For Each o As Order In c.Orders
' Print out the orders.
Console.WriteLine(vbTab & vbTab & "OrderID: {0} - Freight: ${1}", _
o.OrderID, o.Freight)
Next
' Load the next page of Orders.
Dim ordersResponse = _
context.LoadProperty(c, "Orders", nextOrdersLink)
nextOrdersLink = ordersResponse.GetContinuation()
End While
Next
' Get the next link, and continue while there is a next link.
nextLink = response.GetContinuation()
Loop While nextLink IsNot Nothing
Catch ex As DataServiceQueryException
Throw New ApplicationException( _
"An error occurred during query execution.", ex)
End Try
// Create the DataServiceContext using the service URI.
NorthwindEntities context = new NorthwindEntities(svcUri);
DataServiceQueryContinuation<Customer> nextLink = null;
int pageCount = 0;
int innerPageCount = 0;
try
{
// Execute the query for all customers and related orders,
// and get the response object.
var response =
context.Customers.AddQueryOption("$expand", "Orders")
.Execute() as QueryOperationResponse<Customer>;
// With a paged response from the service, use a do...while loop
// to enumerate the results before getting the next link.
do
{
// Write the page number.
Console.WriteLine("Customers Page {0}:", ++pageCount);
// If nextLink is not null, then there is a new page to load.
if (nextLink != null)
{
// Load the new page from the next link URI.
response = context.Execute<Customer>(nextLink)
as QueryOperationResponse<Customer>;
}
// Enumerate the customers in the response.
foreach (Customer c in response)
{
Console.WriteLine("\tCustomer Name: {0}", c.CompanyName);
Console.WriteLine("\tOrders Page {0}:", ++innerPageCount);
// Get the next link for the collection of related Orders.
DataServiceQueryContinuation<Order> nextOrdersLink =
response.GetContinuation(c.Orders);
while (nextOrdersLink != null)
{
foreach (Order o in c.Orders)
{
// Print out the orders.
Console.WriteLine("\t\tOrderID: {0} - Freight: ${1}",
o.OrderID, o.Freight);
}
// Load the next page of Orders.
var ordersResponse = context.LoadProperty(c, "Orders", nextOrdersLink);
nextOrdersLink = ordersResponse.GetContinuation();
}
}
}
// Get the next link, and continue while there is a next link.
while ((nextLink = response.GetContinuation()) != null);
}
catch (DataServiceQueryException ex)
{
throw new ApplicationException(
"An error occurred during query execution.", ex);
}
Siehe auch
Aufgaben
Gewusst wie: Laden von verknüpften Entitäten (WCF Data Services)