Implementing Business Logic - ASP.NET Dynamic Data - page 274

Instead, change the ObjectContext class in your project so that it notifies the entity
objects before they are saved and allows the entity objects to execute property interaction
rules before the validation is performed. For example, the Unleashed.EntityFramework
assembly in the sample solution accompanying this topic defines an interface called
ISavableObject (for consistency with the built-in IValidatableObject interface), that
entity classes can implement when they require property interaction logic.
interface ISavableObject
{
void BeforeSave(ObjectStateEntry stateEntry);
}
In the Order entity class, you can now implement this interface and have the BeforeSave
method get the original value of the OrderStatus property from the ObjectStateEntry ,
compare it to the current value in the OrderStatus property itself, and set the
SubmittedDate property with the system date and time.
partial class Order : ISavableObject
{
public void BeforeSave(ObjectStateEntry stateEntry)
{
byte? oldStatus = (byte)DataModel.OrderStatus.Draft;
if (stateEntry.State == EntityState.Modified)
oldStatus = stateEntry.OriginalValues.Get(() => this.OrderStatus);
if (this.OrderStatus == (byte)DataModel.OrderStatus.Submitted &&
oldStatus == (byte)DataModel.OrderStatus.Draft)
{
this.SubmittedDate = DateTime.Now;
}
}
}
The UnleashedObjectContext class calls the BeforeSave method of each entity object that
implements the ISavableObject interface.
partial class UnleashedObjectContext
{
private void BeforeSaveChanges(ObjectStateEntry stateEntry)
{
var savable = stateEntry.Entity as ISavableObject;
if (savable != null)
savable.BeforeSave(stateEntry);
if (stateEntry.State != EntityState.Deleted)
this.Validate(stateEntry);
}
}