Cómo: Filtrar en el nivel de contexto de datos (LINQ to SQL)
Actualización: November 2007
Puede filtrar EntitySets en el nivel de DataContext. Tales filtros se aplican a todas las consultas realizadas con esa instancia de DataContext.
Ejemplo
En el ejemplo siguiente, se usa DataLoadOptions.AssociateWith(LambdaExpression) para filtrar los pedidos de clientes previamente cargados por ShippedDate.
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);
}
}
}