Programming Entity Framework - Cdn.oreilly.com

Because the class and property names align exactly with the entity and property names,
Entity Framework will be able to work out the mapping between the classes and the
entities, but you’re not done yet.
Since these classes cannot rely on the EntityObject to communicate back to an
ObjectContext, or even know that there is such a thing as an ObjectContext, the
context will need another way to manage these classes so that it can perform its job of
executing queries, returning objects, persisting changes to the database, and so forth.
Creating an ObjectContext Class to Deliver the POCOs
The Contact and Address classes have no knowledge at all about the Entity
Framework. This is a good thing as it is the desired effect. However, we need to let the
Entity Framework be aware of the classes.
Recall that the default code generator not only created the entity classes, but also created
a class that inherited from ObjectContext. We don’t have one of those yet. The next
step is to create your own class that inherits from ObjectContext and let it know
about your custom classes. Once you have done this, the ObjectContext will do its
job of querying, materializing, and managing the custom classes.
For the sake of this simple demo, I am having you put everything into a
single project. This is not the proper way to architect this type of
solution, but is a simpler way to be introduced to the basic concepts.
We’ll separate things out properly in the next example.
Create a new class called Entities and add the code in Example 13-3 which emulates
what you’ve seen in previous ObjectContext classes.
Example 13-3. An ObjectContext class that works with the Contact and Address classes
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.Objects;
namespace Chapter13SimplePOCO
{
class Entities : ObjectContext
{
private ObjectSet _contacts;
private ObjectSet _addresses;
public Entities()
: base("name=POCOEntities", "POCOEntities")
{
_contacts = CreateObjectSet();
_addresses = CreateObjectSet();
}
public ObjectSet Contacts
{
get
{
return _contacts;