Procedura: aggiungere opzioni di query a una query del servizio dati (WCF Data Services)

WCF Data Services consente di eseguire query su un servizio dati da un'applicazione client basata su Framework .NET utilizzando le classi del servizio dati client generate. Il modo più semplice per conseguire questo risultato consiste nel creare un 'espressione di query LINQ (Language Integrated Query) con le opzioni query desiderate. È inoltre possibile chiamare una serie di metodi di query LINQ per creare una query equivalente. È infine possibile utilizzare il metodo AddQueryOption per aggiungere opzioni query a una query. In ciascuno di questi casi l'URI generato dal client include il set di entità richiesto con le opzioni query selezionate applicate. Per ulteriori informazioni, vedere Esecuzione di query sul servizio dati (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 creare un'espressione di query LINQ che restituisce solo gli ordini con un costo di spedizione maggiore di 30 dollari e ordina i risultati in senso decrescente in base alla data di spedizione.

' Create the DataServiceContext using the service URI.
Dim context = New NorthwindEntities(svcUri)

' Define a query for orders with a Freight value greater than 30
' and that is ordered by the ship date, descending.
Dim selectedOrders = From o In context.Orders _
        Where (o.Freight > 30) _
        Order By o.ShippedDate Descending _
        Select o

Try
    ' Enumerate over the results of the query.
    For Each order As Order In selectedOrders
        Console.WriteLine("Order ID: {0} - Ship Date: {1} - Freight: {2}", _
                order.OrderID, order.ShippedDate, order.Freight)
    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 query for orders with a Freight value greater than 30
// and that is ordered by the ship date, descending.
var selectedOrders = from o in context.Orders
                     where o.Freight > 30
                     orderby o.ShippedDate descending 
                     select o;

try
{
    // Enumerate over the results of the query.
    foreach (Order order in selectedOrders)
    {
        Console.WriteLine("Order ID: {0} - Ship Date: {1} - Freight: {2}",
            order.OrderID, order.ShippedDate, order.Freight);
    }
}
catch (DataServiceQueryException ex)
{
    throw new ApplicationException(
        "An error occurred during query execution.", ex);
}

Nell'esempio seguente viene illustrato come creare una query LINQ equivalente alla query precedente tramite i metodi di query LINQ.

' Create the DataServiceContext using the service URI.
Dim context = New NorthwindEntities(svcUri)

' Define a query for orders with a Freight value greater than 30
' and that is ordered by the ship date, descending.
Dim selectedOrders = context.Orders _
                     .Where(Function(o) o.Freight.Value > 30) _
                     .OrderByDescending(Function(o) o.ShippedDate)

Try
    ' Enumerate over the results of the query.
    For Each order As Order In selectedOrders

        Console.WriteLine("Order ID: {0} - Ship Date: {1} - Freight: {2}", _
                order.OrderID, order.ShippedDate, order.Freight)
    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 query for orders with a Freight value greater than 30
// and that is ordered by the ship date, descending.
var selectedOrders = context.Orders
                    .Where(o => o.Freight > 30)
                    .OrderByDescending(o => o.ShippedDate);

try
{
    // Enumerate over the results of the query.
    foreach (Order currentOrder in selectedOrders)
    {
        Console.WriteLine("Order ID: {0} - Ship Date: {1} - Freight: {2}",
            currentOrder.OrderID, currentOrder.ShippedDate, 
            currentOrder.Freight);
    }
}
catch (DataServiceQueryException ex)
{
    throw new ApplicationException(
        "An error occurred during query execution.", ex);
}

Nell'esempio seguente viene illustrato come utilizzare il metodo AddQueryOption per creare un oggetto DataServiceQuery equivalente agli esempi precedenti.

' Create the DataServiceContext using the service URI.
Dim context = New NorthwindEntities(svcUri)

' Define a query for orders with a Freight value greater than 30
' and that is ordered by the ship date, descending.
Dim selectedOrders As DataServiceQuery(Of Order) = context.Orders _
.AddQueryOption("$filter", "Freight gt 30") _
.AddQueryOption("$orderby", "OrderID desc")

Try
    ' Enumerate over the results of the query.
    For Each order As Order In selectedOrders
        Console.WriteLine("Order ID: {0} - Ship Date: {1} - Freight: {2}", _
                order.OrderID, order.ShippedDate, order.Freight)
    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 query for orders with a Freight value greater than 30
// and that is ordered by the ship date, descending.
DataServiceQuery<Order> selectedOrders = context.Orders
    .AddQueryOption("$filter", "Freight gt 30")
    .AddQueryOption("$orderby", "OrderID desc");

try
{
    // Enumerate over the results of the query.
    foreach (Order order in selectedOrders)
    {
        Console.WriteLine("Order ID: {0} - Ship Date: {1} - Freight: {2}", 
            order.OrderID, order.ShippedDate, order.Freight);
    }
}
catch (DataServiceQueryException ex)
{
    throw new ApplicationException(
        "An error occurred during query execution.", ex);
}

Nell'esempio seguente viene illustrato come utilizzare l'opzione query $orderby per filtrare e ordinare gli oggetti Orders restituiti in base alla proprietà Freight.

' Create the DataServiceContext using the service URI.
Dim context = New NorthwindEntities(svcUri)

' Define a query for orders with a Freight value greater than 30
' that also orders the result by the Freight value, descending.
Dim selectedOrders As DataServiceQuery(Of Order) = _
context.Orders.AddQueryOption("$orderby", "Freight gt 30 desc")

Try
    ' Enumerate over the results of the query.
    For Each order As Order In selectedOrders
        Console.WriteLine("Order ID: {0} - Freight: {1}", _
                order.OrderID, order.Freight)
    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 query for orders with a Freight value greater than 30
// that also orders the result by the Freight value, descending.
DataServiceQuery<Order> selectedOrders = context.Orders
    .AddQueryOption("$orderby", "Freight gt 30 desc");

try
{
    // Enumerate over the results of the query.
    foreach (Order order in selectedOrders)
    {
        Console.WriteLine("Order ID: {0} - Freight: {1}",
            order.OrderID, order.Freight);
    }
}
catch (DataServiceQueryException ex)
{
    throw new ApplicationException(
        "An error occurred during query execution.", ex);
}

Vedere anche

Attività

Procedura: proiettare i risultati delle query (WCF Data Services)

Concetti

Esecuzione di query sul servizio dati (WCF Data Services)