如何：执行数据服务查询（WCF 数据服务）
通过 WCF 数据服务 可以使用生成的客户端数据服务类，从基于 .NET Framework 的客户端应用程序查询数据服务。 可以使用下列方法之一执行查询：
针对从 Add Data Service Reference 工具所生成的 DataServiceContext 获取的命名 DataServiceQuery 执行 LINQ 查询。
隐式枚举从 Add Data Service Reference 工具所生成的 DataServiceContext 获取的命名 DataServiceQuery。
显式调用 DataServiceQuery 的 Execute 方法，或显式调用用于异步执行的 BeginExecute 方法。
有关更多信息，请参见查询数据服务（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
下面的示例演示如何定义和执行针对 Northwind 数据服务返回所有 Customers 的 LINQ 查询。
' Create the DataServiceContext using the service URI.
Dim context = New NorthwindEntities(svcUri)
Try
' Define a LINQ query that returns all customers.
Dim allCustomers = From cust In context.Customers _
Select cust
' Enumerate over the query obtained from the context.
For Each customer As Customer In allCustomers
Console.WriteLine("Customer Name: {0}", customer.CompanyName)
Next
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);
try
{
// Define a LINQ query that returns all customers.
var allCustomers = from cust in context.Customers
select cust;
// Enumerate over the query obtained from the context.
foreach (Customer customer in allCustomers)
{
Console.WriteLine("Customer Name: {0}", customer.CompanyName);
}
}
catch (DataServiceQueryException ex)
{
throw new ApplicationException(
"An error occurred during query execution.", ex);
}
下面的示例演示如何使用“Add Data Service Reference”工具所生成的上下文来隐式执行针对 Northwind 数据服务返回所有 Customers 的查询。 该上下文自动确定请求的 Customers 实体集的 URI。 在发生枚举时隐式执行该查询。
' Create the DataServiceContext using the service URI.
Dim context = New NorthwindEntities(svcUri)
' Define a new query for Customers.
Dim query As DataServiceQuery(Of Customer) = context.Customers
Try
' Enumerate over the query result, which is executed implicitly.
For Each customer As Customer In query
Console.WriteLine("Customer Name: {0}", customer.CompanyName)
Next
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);
// Define a new query for Customers.
DataServiceQuery<Customer> query = context.Customers;
try
{
// Enumerate over the query result, which is executed implicitly.
foreach (Customer customer in query)
{
Console.WriteLine("Customer Name: {0}", customer.CompanyName);
}
}
catch (DataServiceQueryException ex)
{
throw new ApplicationException(
"An error occurred during query execution.", ex);
}
下面的示例演示如何使用 DataServiceContext 显式执行针对 Northwind 数据服务返回所有 Customers 的查询。
' Define a request URI that returns Customers.
Dim customersUri = New Uri(svcUri, "Northwind.svc/Customers")
' Create the DataServiceContext using the service URI.
Dim context = New DataServiceContext(svcUri)
Try
' Enumerate over the query result.
For Each customer As Customer In context.Execute(Of Customer)(customersUri)
Console.WriteLine("Customer Name: {0}", customer.CompanyName)
Next
Catch ex As DataServiceQueryException
Throw New ApplicationException( _
"An error occurred during query execution.", ex)
End Try
// Define a request URI that returns Customers.
Uri customersUri = new Uri(svcUri, "Northwind.svc/Customers");
// Create the DataServiceContext using the service URI.
DataServiceContext context = new DataServiceContext(svcUri);
try
{
// Enumerate over the query result.
foreach (Customer customer in context.Execute<Customer>(customersUri))
{
Console.WriteLine("Customer Name: {0}", customer.CompanyName);
}
}
catch (DataServiceQueryException ex)
{
throw new ApplicationException(
"An error occurred during query execution.", ex);
}