mò qã¸Ec@sfdZdklZdklZdefd„ƒYZdefd„ƒYZdefd„ƒYZd S( sPPersistence Interfaces $Id: interfaces.py 40664 2005-12-09 16:19:03Z tim_one $ (s Interface(s Attributet IPersistentcBsktZdZedƒZedƒZedƒZedƒZd„Zd„Z d„Z d„Z d „Z RS( s2Python persistent interface A persistent object can be in one of several states: - Unsaved The object has been created but not saved in a data manager. In this state, the _p_changed attribute is non-None and false and the _p_jar attribute is None. - Saved The object has been saved and has not been changed since it was saved. In this state, the _p_changed attribute is non-None and false and the _p_jar attribute is set to a data manager. - Sticky This state is identical to the saved state except that the object cannot transition to the ghost state. This is a special state used by C methods of persistent objects to make sure that state is not unloaded in the middle of computation. In this state, the _p_changed attribute is non-None and false and the _p_jar attribute is set to a data manager. There is no Python API for detecting whether an object is in the sticky state. - Changed The object has been changed. In this state, the _p_changed attribute is true and the _p_jar attribute is set to a data manager. - Ghost the object is in memory but its state has not been loaded from the database (or its state has been unloaded). In this state, the object doesn't contain any application data. In this state, the _p_changed attribute is None, and the _p_jar attribute is set to the data manager from which the object was obtained. In all the above, _p_oid (the persistent object id) is set when _p_jar first gets set. The following state transitions are possible: - Unsaved -> Saved This transition occurs when an object is saved in the database. This usually happens when an unsaved object is added to (e.g. as an attribute or item of) a saved (or changed) object and the transaction is committed. - Saved -> Changed Sticky -> Changed Ghost -> Changed This transition occurs when someone sets an attribute or sets _p_changed to a true value on a saved, sticky or ghost object. When the transition occurs, the persistent object is required to call the register() method on its data manager, passing itself as the only argument. Prior to ZODB 3.6, setting _p_changed to a true value on a ghost object was ignored (the object remained a ghost, and getting its _p_changed attribute continued to return None). - Saved -> Sticky This transition occurs when C code marks the object as sticky to prevent its deactivation. - Saved -> Ghost This transition occurs when a saved object is deactivated or invalidated. See discussion below. - Sticky -> Saved This transition occurs when C code unmarks the object as sticky to allow its deactivation. - Changed -> Saved This transition occurs when a transaction is committed. After saving the state of a changed object during transaction commit, the data manager sets the object's _p_changed to a non-None false value. - Changed -> Ghost This transition occurs when a transaction is aborted. All changed objects are invalidated by the data manager by an abort. - Ghost -> Saved This transition occurs when an attribute or operation of a ghost is accessed and the object's state is loaded from the database. Note that there is a separate C API that is not included here. The C API requires a specific data layout and defines the sticky state. About Invalidation, Deactivation and the Sticky & Ghost States The sticky state is intended to be a short-lived state, to prevent an object's state from being discarded while we're in C routines. It is an error to invalidate an object in the sticky state. Deactivation is a request that an object discard its state (become a ghost). Deactivation is an optimization, and a request to deactivate may be ignored. There are two equivalent ways to request deactivation: - call _p_deactivate() - set _p_changed to None There are two ways to invalidate an object: call the _p_invalidate() method (preferred) or delete its _p_changed attribute. This cannot be ignored, and is used when semantics require invalidation. Normally, an invalidated object transitions to the ghost state. However, some objects cannot be ghosts. When these objects are invalidated, they immediately reload their state from their data manager, and are then in the saved state. s¬The data manager for the object. The data manager implements the IPersistentDataManager interface. If there is no data manager, then this is None. sNThe object id. It is up to the data manager to assign this. The special value None is reserved to indicate that an object id has not been assigned. Non-None object ids must be non-empty strings. The 8-byte string ''*8 (8 NUL bytes) is reserved to identify the database root object. sPThe persistent state of the object. This is one of: None -- The object is a ghost. false but not None -- The object is saved (or has never been saved). true -- The object has been modified since it was last saved. The object state may be changed by assigning or deleting this attribute; however, assigning None is ignored if the object is not in the saved state, and may be ignored even if the object is in the saved state. At and after ZODB 3.6, setting _p_changed to a true value for a ghost object activates the object; prior to 3.6, setting _p_changed to a true value on a ghost object was ignored. Note that an object can transition to the changed state only if it has a data manager. When such a state change occurs, the 'register' method of the data manager must be called, passing the persistent object. Deleting this attribute forces invalidation independent of existing state, although it is an error if the sticky state is current. sËThe object serial number. This member is used by the data manager to distiguish distinct revisions of a given persistent object. This is an 8-byte string (not Unicode). cCsdS(sŒGet the object data. The state should not include persistent attributes ("_p_name"). The result must be picklable. N((((t4/data/zmath/zope/lib/python/persistent/interfaces.pyt __getstate__ÖscCsdS(sSet the object data. N((tstate((Rt __setstate__ÝscCsdS(s]Activate the object. Change the object to the saved state if it is a ghost. N((((Rt _p_activateáscCsdS(s$Deactivate the object. Possibly change an object in the saved state to the ghost state. It may not be possible to make some persistent objects ghosts, and, for optimization reasons, the implementation may choose to keep an object in the saved state. N((((Rt _p_deactivateçscCsdS(s Invalidate the object. Invalidate the object. This causes any data to be thrown away, even if the object is in the changed state. The object is moved to the ghost state; further accesses will cause object data to be reloaded. N((((Rt _p_invalidateðs( t__name__t __module__t__doc__t Attributet_p_jart_p_oidt _p_changedt _p_serialRRRRR(((RRs †      tIPersistentNoReadConflictscBstZd„ZRS(NcCsdS(séHook for subclasses to prevent read conflict errors. A specific persistent object type can define this method and have it return true if the data manager should ignore read conflicts for this object. N((((Rt_p_independentús(RR R(((RRùstIPersistentDataManagercBs)tZdZd„Zd„Zd„ZRS(s®Provide services for managing persistent state. This interface is used by a persistent object to interact with its data manager in the context of a transaction. cCsdS(sñLoad the state for the given object. The object should be in the ghost state. The object's state will be set and the object will end up in the saved state. The object must provide the IPersistent interface. N((tobject((Rtsetstate scCsdS(sáReturn copy of 'obj' that was written by transaction 'tid'. The returned object does not have the typical metadata (_p_jar, _p_oid, _p_serial) set. I'm not sure how references to other peristent objects are handled. Parameters obj: a persistent object from this Connection. tid: id of a transaction that wrote an earlier revision. Raises KeyError if tid does not exist or if tid deleted a revision of obj. N((tobjttid((Rtoldstates cCsdS(sRegister an IPersistent with the current transaction. This method must be called when the object transitions to the changed state. A subclass could override this method to customize the default policy of one transaction manager for each thread. N((R((Rtregister#s(RR R RRR(((RRs  N(R tzope.interfacet InterfaceR RRR(RR RRR((Rt?s   ã