HOW TO：執行資料服務查詢 (WCF Data Services)
WCF Data Services 可讓您使用所產生的用戶端資料服務類別，從以 .NET Framework 為基礎的用戶端應用程式查詢資料服務。 您可以使用下列其中一種方法執行查詢：
針對您從 Add Data Service Reference 工具所產生之 DataServiceContext 取得的具名 DataServiceQuery 執行 LINQ 查詢。
以隱含的方式列舉您從 Add Data Service Reference 工具所產生之 DataServiceContext 取得的具名 DataServiceQuery。
透過在 DataServiceQuery 呼叫 Execute 方法或 BeginExecute 方法，明確地進行非同步執行。
如需詳細資訊，請參閱查詢資料服務 (WCF Data Services)。
本主題的範例使用 Northwind 範例資料服務，以及自動產生的用戶端資料服務類別。 此服務和用戶端資料類別會在您完成 WCF Data Services 快速入門時建立。
範例
下列範例示範如何定義與執行針對 Northwind 資料服務傳回所有 Customers 的 LINQ 查詢。
' 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);
}
下列範例示範如何使用 Add Data Service Reference 工具所產生的內容，隱含地執行會針對 Northwind 資料服務傳回所有 Customers 的查詢。 內容會自動判斷所要求之 Customers 實體集的 URI。 發生列舉時會隱含執行查詢。
' 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);
}
下列範例示範如何使用 DataServiceContext 明確地執行針對 Northwind 資料服務傳回所有 Customers 的查詢。
' 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);
}