Optional Storage Manager Reference in Entities

When a reference to the loading storage is needed in entities, e.g. usage of different tenants or to store its internal state in a tailored fashion, this can be done by this little trick.

If an entity type contains one or more transient fields with field type compatible to Persister, the updating processing during loading will set the Persister instance (e.g. an EmbeddedStorageManager instance) used to load the entity instance to those fields.

The fields must be transient to exclude them from the persistent form of the entity.
Checking for transient fields is only the default implementation. The checking logic can be customized via PersistenceFoundation#setFieldEvaluatorPersistable.

A more precise check for Persister fields can be customized via PersistenceFoundation#setFieldEvaluatorPersister.
Note, however, that the check for compatibility with the Persister type is done in any case to avoid inconsistencies/crashes.

If no applicable field is found, nothing happens and no additional meta data is kept in memory. This feature is completely optional.

class MyEntity
	String name ;
	int    value;

	transient Persister persister;

Upon loading an instance of class MyEntity, a reference to the Persister used to load it is set to its field persister.