Occurs before changes to an object are persisted to the data source.
Assembly: System.Web.Entity (in System.Web.Entity.dll)
The event is raised before changes to the properties of an object are persisted to the data source. The 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.
Handle the event if you must modify the ObjectStateEntry for the object to set different original values for concurrency control. For more information, see Saving Changes and Managing Concurrency (Entity Framework).
If an error occurs when instantiating an object or modifying properties, the event is raised and the Exception property of the EntityDataSourceChangingEventArgs object is set to the returned Exception.
When you handle the exception in the 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.