The Updating event is raised before changes to the properties of an object are persisted to the data source. The Updating event enables you to modify or verify changes to the object, supply a different object, or cancel the operation before the changes are persisted. You can access the modified object from the Entity property of the EntityDataSourceChangingEventArgs object. If supplying a different object, the user is responsible for setting the correct entity type in the Entity property.
When you handle the exception in the Updating event handler, set the ExceptionHandled property to true. This prevents the exception from being raised again. When you specify a value of false for the ExceptionHandled property, the EntityDataSource re-raises the exception.