WCF 数据服务 允许数据服务限制单个响应源中返回的实体数。在此情况下，源中的最后一项包含指向下一页数据的链接。通过调用执行 DataServiceQuery 时返回的 QueryOperationResponse 的 GetContinuation 方法可以获取下一页数据的 URI。然后，可以使用此对象所表示的 URI 加载下一页结果。有关更多信息，请参见加载延迟的内容（WCF 数据服务）。
本主题中的示例使用 Northwind 示例数据服务和自动生成的客户端数据服务类。此服务和这些客户端数据类是在完成 WCF 数据服务快速入门时创建的。
示例
下面的示例使用 do¡while 循环从数据服务的分页结果中加载 Customers 实体。
VB
' Create the DataServiceContext using the service URI.
Dim context = New NorthwindEntities(svcUri)
Dim token As DataServiceQueryContinuation(Of Customer) = Nothing
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()
' 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("\tCustomer 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
C#
// Create the DataServiceContext using the service URI.
NorthwindEntities context = new NorthwindEntities(svcUri);
DataServiceQueryContinuation<Customer> token = null;
;
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);
}
下面的示例返回每个 Customers 实体的相关 Orders 实体，并使用 do¡while 循环从数据服务中加载 Customers 实体页以及使用嵌套的 while 循环从数据服务中加载相关的 Orders 实体的页。
VB
' Create the DataServiceContext using the service URI.
Dim context = New NorthwindEntities(svcUri)
Dim nextLink As DataServiceQueryContinuation(Of Customer) = Nothing
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("\tCustomer Name: {0}", c.CompanyName)
Console.WriteLine()
' 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("\t\tOrderID: {0} - Freight: ${1}", _
o.OrderID, o.Freight)
Next
' Load the next page of Orders.
Dim ordersResponse = _
context.LoadProperty(c, "Orders", nextOrdersLink)
nextOrdersLink = ordersResponse.GetContinuation()
End While
Next
' Get the next link, and continue while there is a next link.
nextLink = response.GetContinuation()
Loop While nextLink IsNot Nothing
Catch ex As DataServiceQueryException
Throw New ApplicationException( _
"An error occurred during query execution.", ex)
End Try
C#
// Create the DataServiceContext using the service URI.
NorthwindEntities context = new NorthwindEntities(svcUri);
DataServiceQueryContinuation<Customer> nextLink = null;
;
;
try
{
// Execute the query for all customers and related orders,
// and get the response object.
var response =
context.Customers.AddQueryOption("$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);
}