Programming Entity Framework - Cdn.oreilly.com

loading on navigation properties even if you do not set up the class to enable change
tracking.
There is one more rule for enabling lazy loading on the navigation properties. Navigation
properties that point to collections must be an ICollection. The
ObjectContext will take care of the rest of the work for you.
Example 13-9 shows the Addresses navigation property of the Contact class as a
virtual property.
VB
C#
Example 13-9. Enabling POCO classes to use a proxy for lazy loading
Public Overridable Property Addresses() As ICollection(Of Address)
public virtual ICollection Addresses {get; set;}
Example 13-10 displays a method you can add to your console app to check three things
for you. First, it verifies that the context recognizes you have modified the contact using
the ObjectStateManager. Next, it will automatically load the Addresses. Finally,
it saves your changes to the POCO Contact back to the database.
Example 13-10. Verifying change tracking
private static void VerifyVirtualChangeTracking()
{
using (Entities context = new Entities())
{
var contact = context.Contacts.First();
contact.LastName = "Zappos";
contact.FirstName = "Zelly";
int modifiedEntities = context.ObjectStateManager.
GetObjectStateEntries(System.Data.EntityState.Modified).Count();
ICollection addresses = contact.Addresses;
//break to verify that modifiedEntities is 1 and that addresses is not null
context.SaveChanges();
}
}
You can put a breakpoint on the last line of code (context.SaveChanges(););
when it breaks, you can check in the debugger to see what’s in modifiedEntities
and addresses just before SaveChanges is called, as noted in the comment.
Exploring the Proxy Classes
When debugging code that uses these new classes, it is eye-opening to take a closer look
at the classes.
Figure 13-2 shows the Contact that you queried and edited in Example 13-10.