Entity Framework - ASP.NET Dynamic Data - page 60

Entity Lifecycle
As you already know, in addition to its formidable querying capabilities, the Entity
Framework also helps you implement typical data access scenarios, such as creating a new
entity, finding an existing entity, and modifying or deleting it. To do this, the
ObjectContext keeps track of all entities throughout their lifecycles—from creation to
modification to deletion.
Tracking Changes
When a new entity instance is added to an ObjectContext , the context records its state as
Added . The following code shows how to examine entity state changes:
Product p = new Product() { ProductName = “Mukuzani” };
context.Products.AddObject(p);
Console.WriteLine(context.ObjectStateManager.GetObjectStateEntry(p).State);
context.SaveChanges();
Console.WriteLine(context.ObjectStateManager.GetObjectStateEntry(p).State);
The ObjectStateManager property of the ObjectContext class returns the actual object,
keeping track of all new entities that have been added to the context or existing entities
retrieved from the database. In this code, we use its GetObjectStateEntry method to
retrieve an ObjectStateEntry object that represents the newly added Product entity:
[Flags]
public enum EntityState
{
Detached = 1,
Unchanged = 2,
Added = 4,
Deleted = 8,
Modified = 16
}
The State property of the ObjectStateEntry returns an EntityState enumeration value,
which for newly created objects has the value Added until we call the SaveChanges method
of the ObjectContext , at which point the new entity is submitted to the database and the
entity state becomes Unchanged .
In the next example, when an existing Product entity is retrieved from the database, its
state is initially Unchanged . Then, as soon as the Category property is assigned, it becomes
Modified . After the SaveChanges method is called and the changes are submitted to the
database, the entity state becomes Unchanged again: