Cómo: Cambiar las relaciones entre entidades POCO (Entity Framework)
Cuando la creación de objetos proxy está deshabilitada o cuando una entidad POCO se crea sin su objeto proxy, debe llamar al método DetectChanges sobre el ObjectContext para sincronizar los cambios con el ObjectStateManager. Además de detectar cambios en propiedades escalares, este método detecta cambios en relaciones, incluidos los de agregar, eliminar o cambiar un objeto relacionado. Para obtener más información, vea Realizar el seguimiento de los cambios en entidades POCO (Entity Framework). El método SaveChanges llama a DetectChanges, de modo que no tenga que llamar explícitamente a DetectChanges si no necesita una sincronización inmediata de las relaciones.
El ejemplo de este tema utiliza las clases de datos POCO personalizadas que se definen en Cómo: Definir entidades POCO (Entity Framework) y un modelo de datos basado en AdventureWorks que se define en Cómo: Personalizar archivos de asignación y modelado para trabajar con objetos personalizados (Entity Framework).
Ejemplo
En este ejemplo se cambia el contacto actual para un pedido a un contacto diferente. El método SaveChanges llama al método DetectChanges antes de guardar los cambios en el origen de datos.
Using context As New POCOAdventureWorksEntities()
' Disable proxy object creation.
context.ContextOptions.ProxyCreationEnabled = False
Try
' Define the order and new address IDs.
Dim orderId As Integer = 43659
Dim differentContactID As Integer = 5
Dim order As Order = context.Orders.Include("Contact").Where(Function(o) o.SalesOrderID = orderId).First()
' Get contact to change to.
Dim differentContact As Contact = context.Contacts.First(Function(c) c.ContactID = differentContactID)
' The current contact.
Console.WriteLine("Original Contact Name: {0}", order.Contact.FirstName)
' The Entity Framework takes care of setting the other end of the relationship
' when you call DetectChanges or SaveChanges (which calls DetectChanges).
' However, there are scenarios when you are not working with ObjectContext
' and will want to fix both ends of the relationship yourself
' (for example, when working with disconnected objects).
' Change the current ContactID to the new ContactID.
order.ContactID = differentContact.ContactID
' Because the change tracking is not enabled
' The state manager will not be updated untill DetectChanges is called.
' If context.ContextOptions.ProxyCreationEnabled was set to true (which is the default)
' The changes would be synchronized righ away.
Console.WriteLine("The contact was updated, but DetectChanges was not yet called. ")
Console.WriteLine("Contact Name: {0}", order.Contact.FirstName)
context.DetectChanges()
Console.WriteLine("After DetectChanges was called. Contact Name: {0}", order.Contact.FirstName)
' Call save the changes, which calls DetectChanges.
context.SaveChanges()
Catch ex As UpdateException
Console.WriteLine(ex.ToString())
Catch ex As InvalidOperationException
Console.WriteLine(ex.ToString())
End Try
End Using
using (POCOAdventureWorksEntities context =
new POCOAdventureWorksEntities())
{
// Disable proxy object creation.
context.ContextOptions.ProxyCreationEnabled = false;
try
{
// Define the order and new address IDs.
int orderId = 43659;
int differentContactID = 5;
Order order =
context.Orders.Include("Contact")
.Where(o => o.SalesOrderID == orderId).First();
// Get contact to change to.
Contact differentContact = context.Contacts.
First(c => c.ContactID == differentContactID);
// The current contact.
Console.WriteLine("Original Contact Name: {0}", order.Contact.FirstName);
// The Entity Framework takes care of setting the other end of the relationship
// when you call DetectChanges or SaveChanges (which calls DetectChanges).
// However, there are scenarios when you are not working with ObjectContext
// and will want to fix both ends of the relationship yourself
// (for example, when working with disconnected objects).
// Change the current ContactID to the new ContactID.
order.ContactID = differentContact.ContactID;
// Because the change tracking is not enabled
// The state manager will not be updated untill DetectChanges is called.
// If context.ContextOptions.ProxyCreationEnabled was set to true (which is the default)
// The changes would be synchronized righ away.
Console.WriteLine("The contact was updated, but DetectChanges was not yet called. ");
Console.WriteLine("Contact Name: {0}", order.Contact.FirstName);
context.DetectChanges();
Console.WriteLine("After DetectChanges was called. Contact Name: {0}",
order.Contact.FirstName);
// Call save the changes, which calls DetectChanges.
context.SaveChanges();
}
catch (UpdateException ex)
{
Console.WriteLine(ex.ToString());
}
catch (InvalidOperationException ex)
{
Console.WriteLine(ex.ToString());
}
}