UR::Object::Ghost(3) Abstract class for representing deleted objects not yet committed


my $obj = Some::Class->get(1234);
$obj->delete(); # $obj is now a UR::DeletedRef
$ghost = Some::Class::Ghost->get(1234);
$ghost->some_method; # Works


Ghost objects are a bookkeeping entity for tracking objects which have been loaded from an external data source, deleted within the application, and not yet committed. This implies that they still exist in the external data source. When the Context is committed, the existence of Ghost objects triggers commands to the external data sources to also delete the object(s). When objects are brought into the Context by querying a data source, they are compared against any ghosts that may already exist, and matching objects are not re-loaded or returned to the user from a call to get(). If the user wants to get Ghost objects, they must call get() explicitly on the Ghost class.

Each class in the system also has an associated Ghost class, the name of which is formed by tacking '::Ghost' to the name of the regular class. Ghost classes do not have ghosts themselves.

Instances of Ghosts are not instantiated with create() directly, they are created as a concequence of deleting a regular object instance. A Ghost can be turned back into a ``live'' object by re-creating it, or rolling back the transaction it was deleted in.


Applications will not, and should not, normally interact with Ghosts. The whole Ghost system is scheduled for elimination as we refactor the Context and software transaction framework.