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<TElement> 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<TElement>。
显式调用 DataServiceQuery<TElement> 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("Customers", UriKind.Relative);
// 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);
}