Change Information of EF

Majors functions and properties of  ObjectContext class:

 

//
// Summary:
//     Gets the object state manager used by the object context to track object
//     changes.
//
// Returns:
//     The System.Data.Objects.ObjectStateManager used by this System.Data.Objects.ObjectContext.
public ObjectStateManager ObjectStateManager { get; }

//
// Summary:
//     Persists all updates to the data source and resets change tracking in the
//     object context.
//
// Returns:
//     The number of objects in an System.Data.EntityState.Added, System.Data.EntityState.Modified,
//     or System.Data.EntityState.Deleted state when System.Data.Objects.ObjectContext.SaveChanges()
//     was called.
//
// Exceptions:
//   System.Data.OptimisticConcurrencyException:
//     An optimistic concurrency violation has occurred in the data source.
[TargetedPatchingOptOut("Performance critical to inline this type of method across NGen image boundaries")]
public int SaveChanges();

Majors functions and properties of ObjectStateManager class:

// Summary:
//     Occurs when entities are added to or removed from the state manager.
public event CollectionChangeEventHandler ObjectStateManagerChanged;

//
// Summary:
//     Returns a collection of System.Data.Objects.ObjectStateEntry objects for
//     objects or relationships with the given state.
//
// Parameters:
//   state:
//     An System.Data.EntityState used to filter the returned System.Data.Objects.ObjectStateEntry
//     objects.
//
// Returns:
//     A collection of System.Data.Objects.ObjectStateEntry objects in the given
//     System.Data.EntityState.
//
// Exceptions:
//   System.ArgumentException:
//     When state is System.Data.EntityState.Detached.
public IEnumerable<ObjectStateEntry> GetObjectStateEntries(EntityState state);

//
// Summary:
//     Returns an System.Data.Objects.ObjectStateEntry for the object or relationship
//     entry with the specified key.
//
// Parameters:
//   key:
//     The System.Data.EntityKey.
//
// Returns:
//     The corresponding System.Data.Objects.ObjectStateEntry for the given System.Data.EntityKey.
//
// Exceptions:
//   System.ArgumentNullException:
//     When key is null.
//
//   System.ArgumentException:
//     When the specified key cannot be found in the state manager.
//
//   System.InvalidOperationException:
//     No entity with the specified System.Data.EntityKey exists in the System.Data.Objects.ObjectStateManager.
public ObjectStateEntry GetObjectStateEntry(EntityKey key);

First, a new racer is added with the AddObject() method of the ObjectSet<T> class. This method adds a new entity with the EntityState.
Added information. Next, a racer with the Lastname Alonso is queried. With this entity class, the Starts
property is incremented and thus the entity is marked with the information EntityState.Modified.

private static void ChangeInformation()
       {
           using (var data = new Formula1Entities())
           {
               var jaime = new Racer
               {
                   Firstname = "Jaime",
                   Lastname = "Alguersuari",
                   Country = "Spain",
                   Starts = 0
               };
               data.Racers.AddObject(jaime);
               Racer fernando = data.Racers.Where("it.Lastname='Alonso'").First();
               fernando.Starts++;
               DisplayState(EntityState.Added.ToString(),
                   data.ObjectStateManager.GetObjectStateEntries(EntityState.Added));
               DisplayState(EntityState.Modified.ToString(),
                     data.ObjectStateManager.GetObjectStateEntries(EntityState.Modified));
               ObjectStateEntry stateOfFernando =
                     data.ObjectStateManager.GetObjectStateEntry(fernando.EntityKey);
               Console.WriteLine("state of Fernando: {0}",
                     stateOfFernando.State.ToString());
               foreach (string modifiedProp in stateOfFernando.GetModifiedProperties())
               {
                   Console.WriteLine("modified: {0}", modifiedProp);
                   Console.WriteLine("original: {0}", stateOfFernando.OriginalValues[modifiedProp]);
                   Console.WriteLine("current: {0}", stateOfFernando.CurrentValues[modifiedProp]);
               }
               int changes = 0;
               try
               {
                   changes += data.SaveChanges();
               }
               catch (OptimisticConcurrencyException ex)
               {
                   data.Refresh(RefreshMode.ClientWins, ex.StateEntries);
                   changes += data.SaveChanges();
               }
               Console.WriteLine("{0} entities changed", changes);

           }
       }
       static void DisplayState(string state, IEnumerable<ObjectStateEntry> entries)
       {
           foreach (var entry in entries)
           {
               var r = entry.Entity as Racer;
               if (r != null)
               {
                   Console.WriteLine("{0}: {1}", state, r.Lastname);
               }
           }
       }