Vorgehensweise: Filtern auf DataContext-Ebene (LINQ to SQL)

Sie können EntitySets auf DataContext-Ebene filtern. Solche Filter gelten für alle Abfragen, die mit dieser DataContext-Instanz erstellt wurden.

Beispiel

Im folgenden Beispiel wird DataLoadOptions.AssociateWith(LambdaExpression) verwendet, um die vorab geladenen Reihenfolgen für Kunden nach ShippedDate zu filtern.

Dim db As New Northwnd("c:\northwnd.mdf")
' Preload Orders for Customer.
' One directive per relationship to be preloaded.
Dim ds As DataLoadOptions = New DataLoadOptions()
ds.LoadWith(Of Customer)(Function(cust) cust.Orders)
ds.AssociateWith(Of Customer)( _
    Function(cust) _
        From ord In cust.Orders _
        Where ord.ShippedDate <> DateTime.Today)

db.LoadOptions = ds

Dim custQuery = From cust In db.Customers _
                Where cust.City = "London" _
                Select cust

For Each custObj In custQuery
    Console.WriteLine("Customer ID: " & custObj.CustomerID)

    For Each ord In custObj.Orders
        Console.WriteLine(vbTab & "Order ID: " & ord.OrderID)

        For Each detail In ord.OrderDetails
            Console.WriteLine(vbTab & vbTab & _
                "Product ID: " & detail.ProductID)
        Next
    Next
Next

Northwnd db = new Northwnd(@"northwnd.mdf");
// Preload Orders for Customer.
// One directive per relationship to be preloaded.
DataLoadOptions ds = new DataLoadOptions();
ds.LoadWith<Customer>(c => c.Orders);
ds.AssociateWith<Customer>
    (c => c.Orders.Where(p => p.ShippedDate != DateTime.Today));
db.LoadOptions = ds;

var custQuery =
    from cust in db.Customers
    where cust.City == "London"
    select cust;

foreach (Customer custObj in custQuery)
{
    Console.WriteLine("Customer ID: {0}", custObj.CustomerID);
    foreach (Order ord in custObj.Orders)
    {
        Console.WriteLine("\tOrder ID: {0}", ord.OrderID);
        foreach (OrderDetail detail in ord.OrderDetails)
        {
            Console.WriteLine("\t\tProduct ID: {0}", detail.ProductID);
        }
    }
}

Siehe auch

Weitere Ressourcen

Abfragekonzepte in LINQ to SQL