Procedura: eseguire query in un batch (WCF Data Services)
Tramite la libreria client di WCF Data Services è possibile eseguire più query sul servizio dati in un unico batch. Per ulteriori informazioni, vedere Invio in batch di operazioni (WCF Data Services).
Nell'esempio riportato in questo argomento vengono utilizzati il servizio dati Northwind di esempio e le classi del servizio dati client generate automaticamente. Questo servizio e le classi di dati client vengono creati al completamento della Guida rapida di WCF Data Services.
Esempio
Nell'esempio seguente viene illustrato come chiamare il metodo ExecuteBatch per eseguire una matrice di oggetti DataServiceRequest contenente query che restituiscono gli oggetti Customers e Products dal servizio dati Northwind. La raccolta di oggetti QueryOperationResponse inclusa nell'oggetto DataServiceResponse restituito viene enumerata, allo stesso modo della raccolta di oggetti inclusa in ogni oggetto QueryOperationResponse.
Dim customerId = "ALFKI"
' Create the DataServiceContext using the service URI.
Dim context = New NorthwindEntities(svcUri)
' Create the separate query URI's, one that returns
' a single customer and another that returns all Products.
Dim customerUri = New Uri(svcUri.AbsoluteUri & _
"/Customers('" & customerId & "')/?$expand=Orders")
Dim productsUri = New Uri(svcUri.AbsoluteUri & _
"/Products")
' Create the query requests.
Dim customerQuery = New DataServiceRequest(Of Customer)(customerUri)
Dim productsQuery = New DataServiceRequest(Of Product)(productsUri)
' Add the query requests to a batch request array.
Dim batchRequests = _
New DataServiceRequest() {customerQuery, productsQuery}
Dim batchResponse As DataServiceResponse
Try
' Execute the query batch and get the response.
batchResponse = context.ExecuteBatch(batchRequests)
If batchResponse.IsBatchResponse Then
' Parse the batchResponse.BatchHeaders.
End If
' Enumerate over the results of the query.
For Each response As QueryOperationResponse In batchResponse
' Handle an error response.
If response.StatusCode > 299 OrElse response.StatusCode < 200 Then
Console.WriteLine("An error occurred.")
Console.WriteLine(response.Error.Message)
Else
' Find the response for the Customers query.
If response.Query.ElementType Is GetType(Customer) Then
For Each customer As Customer In response
Console.WriteLine("Customer: {0}", customer.CompanyName)
For Each order As Order In customer.Orders
Console.WriteLine("Order ID: {0} - Freight: {1}", _
order.OrderID, order.Freight)
Next
Next
' Find the response for the Products query.
ElseIf response.Query.ElementType Is GetType(Product) Then
For Each product As Product In response
Console.WriteLine("Product: {0}", product.ProductName)
Next
End If
End If
Next
' This type of error is raised when the data service returns with
' a response code < 200 or >299 in the top level element.
Catch ex As DataServiceRequestException
' Get the response from the exception.
batchResponse = ex.Response
If (batchResponse.IsBatchResponse) Then
' Parse the batchResponse.BatchHeaders.
End If
For Each response As QueryOperationResponse In batchResponse
If response.Error IsNot Nothing Then
Console.WriteLine("An error occurred.")
Console.WriteLine(response.Error.Message)
End If
Next
End Try
string customerId = "ALFKI";
// Create the DataServiceContext using the service URI.
NorthwindEntities context = new NorthwindEntities(svcUri);
// Create the separate query URI's, one that returns
// a single customer and another that returns all Products.
Uri customerUri = new Uri(svcUri.AbsoluteUri +
"/Customers('" + customerId + "')/?$expand=Orders");
Uri productsUri = new Uri(svcUri.AbsoluteUri +
"/Products");
// Create the query requests.
DataServiceRequest<Customer> customerQuery =
new DataServiceRequest<Customer>(customerUri);
DataServiceRequest<Product> productsQuery =
new DataServiceRequest<Product>(productsUri);
// Add the query requests to a batch request array.
DataServiceRequest[] batchRequests =
new DataServiceRequest[]{customerQuery, productsQuery};
DataServiceResponse batchResponse;
try
{
// Execute the query batch and get the response.
batchResponse = context.ExecuteBatch(batchRequests);
if (batchResponse.IsBatchResponse)
{
// Parse the batchResponse.BatchHeaders.
}
// Enumerate over the results of the query.
foreach (QueryOperationResponse response in batchResponse)
{
// Handle an error response.
if (response.StatusCode > 299 || response.StatusCode < 200)
{
Console.WriteLine("An error occurred.");
Console.WriteLine(response.Error.Message);
}
else
{
// Find the response for the Customers query.
if (response.Query.ElementType == typeof(Customer))
{
foreach (Customer customer in response)
{
Console.WriteLine("Customer: {0}", customer.CompanyName);
foreach (Order order in customer.Orders)
{
Console.WriteLine("Order ID: {0} - Freight: {1}",
order.OrderID, order.Freight);
}
}
}
// Find the response for the Products query.
else if (response.Query.ElementType == typeof(Product))
{
foreach (Product product in response)
{
Console.WriteLine("Product: {0}", product.ProductName);
}
}
}
}
}
// This type of error is raised when the data service returns with
// a response code < 200 or >299 in the top level element.
catch (DataServiceRequestException e)
{
// Get the response from the exception.
batchResponse = e.Response;
if (batchResponse.IsBatchResponse)
{
// Parse the batchResponse.BatchHeaders.
}
foreach (QueryOperationResponse response in batchResponse)
{
if (response.Error != null)
{
Console.WriteLine("An error occurred.");
Console.WriteLine(response.Error.Message);
}
}
}