""" This is the *abstract* django models for many of the database objects in Evennia. A django abstract (obs, not the same as a Python metaclass!) is a model which is not actually created in the database, but which only exists for other models to inherit from, to avoid code duplication. Any model can import and inherit from these classes. Attributes are database objects stored on other objects. The implementing class needs to supply a ForeignKey field attr_object pointing to the kind of object being mapped. TypedObjects are objects 'decorated' with a typeclass - that is, the typeclass (which is a normal Python class implementing some special tricks with its get/set attribute methods, allows for the creation of all sorts of different objects all with the same database object underneath. Usually attributes are used to permanently store things not hard-coded as field on the database object. The admin should usually not have to deal directly with the database object layer. This module also contains the Managers for the respective models; inherit from these to create custom managers. """ try: import cPickle as pickle except ImportError: import pickle import traceback from django.db import models from django.utils.encoding import smart_str from src.utils.idmapper.models import SharedMemoryModel from src.typeclasses import managers from src.utils import logger from src.utils.utils import is_iter # used by Attribute to efficiently identify stored object types. # Note that these have to be updated if directory structure changes. PARENTS = { "typeclass":"src.typeclasses.typeclass.TypeClass", "object":"src.objects.models.ObjectDB", "player":"src.players.models.PlayerDB", "script":"src.scripts.models.ScriptDB", "msg":"src.comms.models.Msg", "channel":"src.comms.models.Channel", "help":"src.help.models.HelpEntry"} # cached typeclasses for all typed models TYPECLASS_CACHE = {} def reset(): "Clean out the typeclass cache" global TYPECLASS_CACHE TYPECLASS_CACHE = {} #------------------------------------------------------------ # # Attributes # #------------------------------------------------------------ class Attribute(SharedMemoryModel): """ Abstract django model. Attributes are things that are specific to different types of objects. For example, a drink container needs to store its fill level, whereas an exit needs to store its open/closed/locked/unlocked state. These are done via attributes, rather than making different classes for each object type and storing them directly. The added benefit is that we can add/remove attributes on the fly as we like. The Attribute class defines the following properties: key - primary identifier mode - which type of data is stored in attribute permissions - perm strings obj - which object the attribute is defined on date_created - when the attribute was created value - the data stored in the attribute """ # # Attribute Database Model setup # # # These databse fields are all set using their corresponding properties, # named same as the field, but withtout the db_* prefix. db_key = models.CharField(max_length=255) # access through the value property db_value = models.TextField(blank=True, null=True) # tells us what type of data is stored in the attribute db_mode = models.CharField(max_length=20, null=True, blank=True) # permissions to do things to this attribute db_permissions = models.CharField(max_length=255, blank=True) # references the object the attribute is linked to (this is set # by each child class to this abstact class) db_obj = None # models.ForeignKey("RefencedObject") # time stamp db_date_created = models.DateTimeField(editable=False, auto_now_add=True) # Database manager objects = managers.AttributeManager() class Meta: "Define Django meta options" abstract = True verbose_name = "Evennia Attribute" verbose_name_plural = "Evennia Attributes" # Wrapper properties to easily set database fields. These are # @property decorators that allows to access these fields using # normal python operations (without having to remember to save() # etc). So e.g. a property 'attr' has a get/set/del decorator # defined that allows the user to do self.attr = value, # value = self.attr and del self.attr respectively (where self # is the object in question). # key property (wraps db_key) #@property def key_get(self): "Getter. Allows for value = self.key" return self.db_key #@key.setter def key_set(self, value): "Setter. Allows for self.key = value" self.db_key = value self.save() #@key.deleter def key_del(self): "Deleter. Allows for del self.key" raise Exception("Cannot delete attribute key!") key = property(key_get, key_set, key_del) # mode property (wraps db_mode) #@property def mode_get(self): "Getter. Allows for value = self.mode" return self.db_mode #@mode.setter def mode_set(self, value): "Setter. Allows for self.mode = value" self.db_mode = value self.save() #@mode.deleter def mode_del(self): "Deleter. Allows for del self.mode" self.db_mode = None self.save() mode = property(mode_get, mode_set, mode_del) # permissions property #@property def permissions_get(self): "Getter. Allows for value = self.permissions. Returns a list of permissions." if self.db_permissions: return [perm.strip() for perm in self.db_permissions.split(',')] return [] #@permissions.setter def permissions_set(self, value): "Setter. Allows for self.permissions = value. Stores as a comma-separated string." if is_iter(value): value = ",".join([str(val).strip().lower() for val in value]) self.db_permissions = value self.save() #@permissions.deleter def permissions_del(self): "Deleter. Allows for del self.permissions" self.db_permissions = "" self.save() permissions = property(permissions_get, permissions_set, permissions_del) # obj property (wraps db_obj) #@property def obj_get(self): "Getter. Allows for value = self.obj" return self.db_obj #@obj.setter def obj_set(self, value): "Setter. Allows for self.obj = value" self.db_obj = value self.save() #@obj.deleter def obj_del(self): "Deleter. Allows for del self.obj" self.db_obj = None self.save() obj = property(obj_get, obj_set, obj_del) # date_created property (wraps db_date_created) #@property def date_created_get(self): "Getter. Allows for value = self.date_created" return self.db_date_created #@date_created.setter def date_created_set(self, value): "Setter. Allows for self.date_created = value" raise Exception("Cannot edit date_created!") #@date_created.deleter def date_created_del(self): "Deleter. Allows for del self.date_created" raise Exception("Cannot delete date_created!") date_created = property(date_created_get, date_created_set, date_created_del) # value property (wraps db_value) #@property def value_get(self): """ Getter. Allows for value = self.value. """ db_value = self.db_value db_mode = self.db_mode try: if not db_mode: # it's a string, just return plain db_value below pass elif db_mode == 'pickle': db_value = pickle.loads(str(db_value)) elif db_mode == 'object': from src.objects.models import ObjectDB db_value = ObjectDB.objects.dbref_search(db_value) elif db_mode == 'script': from src.scripts.models import ScriptDB db_value = ScriptDB.objects.dbref_search(db_value) elif db_mode == 'player': from src.players.models import PlayerDB db_value = PlayerDB.objects.get(id=int(db_value)) elif db_mode == 'msg': from src.comms.models import Msg db_value = Msg.objects.objects.get(id=int(db_value)) elif db_mode == 'channel': from src.comms.models import Channel db_value = Channel.objects.get(id=int(db_value)) elif db_mode == 'help': from src.help.models import HelpEntry db_value = HelpEntry.objects.get(id=int(db_value)) except Exception: logger.log_trace() #TODO: Remove when stable? db_value = None return db_value #@value.setter def value_set(self, new_value): "Setter. Allows for self.value = value" new_value, mode = self._convert_value(new_value) if mode == "pickle": new_value = pickle.dumps(new_value) #,pickle.HIGHEST_PROTOCOL) self.db_value = new_value self.db_mode = mode self.save() #@value.deleter def value_del(self): "Deleter. Allows for del attr.value. This removes the entire attribute." self.delete() value = property(value_get, value_set, value_del) # # # Attribute methods # # def __str__(self): return smart_str("%s(%s)" % (self.key, self.id)) def __unicode__(self): return u"%s(%s)" % (self.key, self.id) def _convert_value(self, in_value): """ We have to be careful as to what we store. Some things, such as django model instances, cannot be directly stored/pickled in an attribute, so we have to be clever about it. Types of objects and how they are handled: * str - stored directly in field * django model object - store its dbref in field * any other python structure - pickle in field """ def has_parent(basepath, obj): "Checks if basepath is somewhere in objs parent tree." try: return any(cls for cls in obj.__class__.mro() if basepath == "%s.%s" % (cls.__module__, cls.__name__)) except (TypeError, AttributeError): # this can occur if we tried to store a class object, not an # instance. Not sure if one should defend against this. return False if isinstance(in_value, basestring): # (basestring matches both str and unicode) # strings we just store directly. return in_value, None if is_iter(in_value): # an iterable. This is normally something to pickle, # but we have to be careful so as to not find # django model instances nested in the iterable. pass #TODO! if not has_parent('django.db.models.base.Model', in_value) \ and not has_parent(PARENTS['typeclass'], in_value): # non-django models that are not strings we pickle #print "type identified: to_pickle" #print "found a non-django parent." return in_value, 'pickle' # this is a db model. Try to determine what type of db object it is. db_type = [parent for parent, path in PARENTS.items() if has_parent(path, in_value)] if db_type and db_type[0] == 'typeclass': # the typeclass alone can't help us, we have to know the db object. db_type = [parent for parent, path in PARENTS.items() if has_parent(path, in_value.dbobj)] if not db_type: # no match; maybe it's a non-model from inside django(?). return in_value, "pickle" # it's a db model. Return its dbref as a string instead. #print "type identified: %s" % db_type[0] return str(in_value.id), db_type[0] #------------------------------------------------------------ # # Typed Objects # #------------------------------------------------------------ class TypedObject(SharedMemoryModel): """ Abstract Django model. This is the basis for a typed object. It also contains all the mechanics for managing connected attributes. The TypedObject has the following properties: key - main name name - alias for key typeclass_path - the path to the decorating typeclass typeclass - auto-linked typeclass date_created - time stamp of object creation permissions - perm strings dbref - #id of object db - persistent attribute storage ndb - non-persistent attribute storage """ # # TypedObject Database Model setup # # # These databse fields are all set using their corresponding properties, # named same as the field, but withtou the db_* prefix. # Main identifier of the object, for searching. Can also # be referenced as 'name'. db_key = models.CharField(max_length=255) # This is the python path to the type class this object is tied to # (the type class is what defines what kind of Object this is) db_typeclass_path = models.CharField(max_length=255, null=True) # Creation date db_date_created = models.DateTimeField(editable=False, auto_now_add=True) # Permissions (access these through the 'permissions' property) db_permissions = models.CharField(max_length=512, blank=True) # Database manager objects = managers.TypedObjectManager() class Meta: """ Django setup info. """ abstract = True verbose_name = "Evennia Database Object" verbose_name_plural = "Evennia Database Objects" ordering = ['-db_date_created', 'id', 'db_typeclass_path', 'db_key'] # Wrapper properties to easily set database fields. These are # @property decorators that allows to access these fields using # normal python operations (without having to remember to save() # etc). So e.g. a property 'attr' has a get/set/del decorator # defined that allows the user to do self.attr = value, # value = self.attr and del self.attr respectively (where self # is the object in question). # key property (wraps db_key) #@property def key_get(self): "Getter. Allows for value = self.key" return self.db_key #@key.setter def key_set(self, value): "Setter. Allows for self.key = value" self.db_key = value self.save() #@key.deleter def key_del(self): "Deleter. Allows for del self.key" raise Exception("Cannot delete objectdb key!") key = property(key_get, key_set, key_del) # name property (wraps db_key too - alias to self.key) #@property def name_get(self): "Getter. Allows for value = self.name" return self.db_key #@name.setter def name_set(self, value): "Setter. Allows for self.name = value" self.db_key = value self.save() #@name.deleter def name_del(self): "Deleter. Allows for del self.name" raise Exception("Cannot delete name!") name = property(name_get, name_set, name_del) # typeclass_path property #@property def typeclass_path_get(self): "Getter. Allows for value = self.typeclass_path" return self.db_typeclass_path #@typeclass_path.setter def typeclass_path_set(self, value): "Setter. Allows for self.typeclass_path = value" self.db_typeclass_path = value self.save() #@typeclass_path.deleter def typeclass_path_del(self): "Deleter. Allows for del self.typeclass_path" self.db_typeclass_path = None self.save() typeclass_path = property(typeclass_path_get, typeclass_path_set, typeclass_path_del) # date_created property #@property def date_created_get(self): "Getter. Allows for value = self.date_created" return self.db_date_created #@date_created.setter def date_created_set(self, value): "Setter. Allows for self.date_created = value" raise Exception("Cannot change date_created!") #@date_created.deleter def date_created_del(self): "Deleter. Allows for del self.date_created" raise Exception("Cannot delete date_created!") date_created = property(date_created_get, date_created_set, date_created_del) # permissions property #@property def permissions_get(self): "Getter. Allows for value = self.name. Returns a list of permissions." if self.db_permissions: return [perm.strip() for perm in self.db_permissions.split(',')] return [] #@permissions.setter def permissions_set(self, value): "Setter. Allows for self.name = value. Stores as a comma-separated string." if is_iter(value): value = ",".join([str(val).strip() for val in value]) self.db_permissions = value self.save() #@permissions.deleter def permissions_del(self): "Deleter. Allows for del self.name" self.db_permissions = "" self.save() permissions = property(permissions_get, permissions_set, permissions_del) # # # TypedObject main class methods and properties # # # Each subclass should set this property to their respective # attribute model (ObjAttribute, PlayerAttribute etc). attribute_model_path = "src.typeclasses.models" attribute_model_name = "Attribute" def __eq__(self, other): return other and hasattr(other, 'id') and self.id == other.id def __str__(self): return smart_str("%s" % self.key) def __unicode__(self): return u"%s" % self.key def __getattribute__(self, propname): """ Will predominantly look for an attribute on this object, but if not found we will check if it might exist on the typeclass instead. Since the typeclass refers back to the databaseobject as well, we have to be very careful to avoid loops. """ try: return object.__getattribute__(self, propname) except AttributeError: # check if the attribute exists on the typeclass instead # (we make sure to not incur a loop by not triggering the # typeclass' __getattribute__, since that one would # try to look back to this very database object.) typeclass = object.__getattribute__(self, 'typeclass') #typeclass = object.__getattribute__(self, 'typeclass') #print " '%s' not on db --> Checking typeclass %s instead." % (propname, typeclass) if typeclass: return object.__getattribute__(typeclass(self), propname) raise #@property def dbref_get(self): """ Returns the object's dbref id on the form #NN. Alternetively, use obj.id directly to get dbref without any #. """ return "#%s" % str(self.id) dbref = property(dbref_get) # typeclass property #@property def typeclass_get(self): """ Getter. Allows for value = self.typeclass. The typeclass is a class object found at self.typeclass_path; it allows for extending the ObjectDB for all different types of objects that the game needs. This property handles loading and initialization of the typeclass on the fly. """ def errmsg(message): """ Helper function to display error. We cannot use self.msg() here since we cannot be sure it's actually available when error occurs; so we have to go to the sessionhandler and echo to all connections. """ from src.server.sessionhandler import SESSIONS for session in SESSIONS: session.msg(message) path = self.db_typeclass_path errstring = "" if not path: # this means we should get the default obj # without giving errors. defpath = self.default_typeclass_path typeclass = self._path_import(defpath) else: typeclass = TYPECLASS_CACHE.get(path, None) if typeclass: # we've imported this before. We're done. return typeclass # not in cache. Import anew. typeclass = self._path_import(path) if not callable(typeclass): # given path failed to import, fallback to default. errstring = " %s" % typeclass # this is an error message if hasattr(typeclass, '__file__'): errstring += "\nThis seems to be just the path to a module. You need" errstring += " to specify the actual typeclass name inside the module too." errstring += "\n Typeclass '%s' failed to load." % path defpath = self.default_typeclass_path errstring += " Using Default class '%s'." % defpath self.db_typeclass_path = defpath self.save() logger.log_errmsg(errstring) typeclass = self._path_import(defpath) errmsg(errstring) if not callable(typeclass): # if typeclass still doesn't exist, we're in trouble. # fall back to hardcoded core class. errstring = " %s\n%s" % (typeclass, errstring) errstring += " Default class '%s' failed to load." % defpath defpath = "src.objects.objects.Object" errstring += "\n Using Evennia's default class '%s'." % defpath self.db_typeclass_path = defpath self.save() logger.log_errmsg(errstring) typeclass = self._path_import(defpath) errmsg(errstring) else: TYPECLASS_CACHE[path] = typeclass return typeclass #@typeclass.deleter def typeclass_del(self): "Deleter. Allows for del self.typeclass (don't allow deletion)" raise Exception("The typeclass property should never be deleted!") typeclass = property(typeclass_get, fdel=typeclass_del) def _path_import(self, path): """ Import a class from a python path of the form src.objects.object.Object """ errstring = "" if not path: # this needs not be bad, it just means # we should use defaults. return None try: modpath, class_name = path.rsplit('.', 1) module = __import__(modpath, fromlist=[class_name]) return module.__dict__[class_name] except ImportError: trc = traceback.format_exc() errstring = "\n%s\nError importing '%s'." % (trc, path) except KeyError: errstring = "No class '%s' was found in module '%s'." errstring = errstring % (class_name, modpath) except Exception: trc = traceback.format_exc() errstring = "\n%s\nImporting '%s' failed." % (trc, path) # return the error. return errstring def is_typeclass(self, other_typeclass, exact=False): """ Returns true if this object has this type OR has a typeclass which is an subclass of the given typeclass. other_typeclass - can be a class object or the python path to such an object. exact - returns true only if the object's type is exactly this typeclass, ignoring parents. """ if callable(other_typeclass): # this is an actual class object. Get the path to it. cls = other_typeclass.__class__ other_typeclass = "%s.%s" % (cls.__module__, cls.__name__) if not other_typeclass: return False if self.db_typeclass_path == other_typeclass: return True if not exact: # check the parent chain. return any([cls for cls in self.typeclass.mro() if other_typeclass == "%s.%s" % (cls.__module__, cls.__name__)]) return False # # Object manipulation methods # # def swap_typeclass(self, new_typeclass, clean_attributes=False): """ This performs an in-situ swap of the typeclass. This means that in-game, this object will suddenly be something else. Player will not be affected. To 'move' a player to a different object entirely (while retaining this object's type), use self.player.swap_object(). Note that this might be an error prone operation if the old/new typeclass was heavily customized - your code might expect one and not the other, so be careful to bug test your code if using this feature! Often its easiest to create a new object and just swap the player over to that one instead. new_typeclass (path/classobj) - type to switch to clean_attributes (bool/list) - will delete all attributes stored on this object (but not any of the database fields such as name or location). You can't get attributes back, but this is often the safest bet to make sure nothing in the new typeclass clashes with the old one. If you supply a list, only those named attributes will be cleared. """ if callable(new_typeclass): # this is an actual class object - build the path cls = new_typeclass.__class__ new_typeclass = "%s.%s" % (cls.__module__, cls.__name__) # Try to set the new path self.db_typeclass_path = new_typeclass.strip() self.save() # this will automatically use a default class if # there is an error with the given typeclass. new_typeclass = self.typeclass(self) if clean_attributes: # Clean out old attributes if is_iter(clean_attributes): for attr in clean_attributes: self.attr(attr, delete=True) for nattr in clean_attributes: if hasattr(self.ndb, nattr): self.nattr(nattr, delete=True) else: #print "deleting attrs ..." self.get_all_attributes() for attr in self.get_all_attributes(): attr.delete() for nattr in self.ndb.all(): del nattr # run hook for this new typeclass new_typeclass.at_object_creation() # # Attribute handler methods # # # Fully persistent attributes. You usually access these # through the obj.db.attrname method. If FULL_PERSISTENCE # is set, you will access these by just obj.attrname instead. # # Helper methods for persistent attributes def has_attribute(self, attribute_name): """ See if we have an attribute set on the object. attribute_name: (str) The attribute's name. """ exec("from %s import %s" % (self.attribute_model_path, self.attribute_model_name)) model = eval("%s" % self.attribute_model_name) attr = model.objects.attr_namesearch(attribute_name, self) return attr.count() > 0 def set_attribute(self, attribute_name, new_value=None): """ Sets an attribute on an object. Creates the attribute if need be. attribute_name: (str) The attribute's name. new_value: (python obj) The value to set the attribute to. If this is not a str, the object will be stored as a pickle. """ attrib_obj = None if self.has_attribute(attribute_name): exec("from %s import %s" % (self.attribute_model_path, self.attribute_model_name)) model = eval("%s" % self.attribute_model_name) #print "attr: model:", self.attribute_model_name attrib_obj = \ model.objects.filter( db_obj=self).filter( db_key__iexact=attribute_name)[0] if attrib_obj: # Save over the existing attribute's value. #print "attr:overwrite: %s.%s = %s" % (attrib_obj.db_obj.key, attribute_name, new_value) attrib_obj.value = new_value else: # Create a new attribute exec("from %s import %s" % (self.attribute_model_path, self.attribute_model_name)) new_attrib = eval("%s()" % self.attribute_model_name) new_attrib.db_key = attribute_name new_attrib.db_obj = self new_attrib.value = new_value #print "attr:new: %s.%s = %s" % (new_attrib.db_obj.key, attribute_name, new_value) def get_attribute(self, attribute_name, default=None): """ Returns the value of an attribute on an object. You may need to type cast the returned value from this function since the attribute can be of any type. attribute_name: (str) The attribute's name. default: What to return if no attribute is found """ if self.has_attribute(attribute_name): try: exec("from %s import %s" % (self.attribute_model_path, self.attribute_model_name)) model = eval("%s" % self.attribute_model_name) attrib = model.objects.filter( db_obj=self).filter( db_key=attribute_name)[0] except Exception: # safety, if something goes wrong (like unsynced db), catch it. logger.log_trace() return default return attrib.value else: return default def del_attribute(self, attribute_name): """ Removes an attribute entirely. attribute_name: (str) The attribute's name. """ exec("from %s import %s" % (self.attribute_model_path, self.attribute_model_name)) model = eval("%s" % self.attribute_model_name) #print "delete attr", model, attribute_name attrs = \ model.objects.attr_namesearch(attribute_name, self) #print "found attrs:", attrs if attrs: attrs[0].delete() def get_all_attributes(self): """ Returns all attributes defined on the object. """ attr_set_all = eval("self.%s_set.all()" % (self.attribute_model_name.lower())) return [attr for attr in attr_set_all] def attr(self, attribute_name=None, value=None, delete=False): """ This is a convenient wrapper for get_attribute, set_attribute, del_attribute and get_all_attributes. If value is None, attr will act like a getter, otherwise as a setter. set delete=True to delete the named attribute. Note that you cannot set the attribute value to None using this method should you want that, use set_attribute for that. """ if attribute_name == None: # act as a list method return self.get_all_attributes() elif delete == True: self.del_attribute(attribute_name) elif value == None: # act as a getter. return self.get_attribute(attribute_name) else: # act as a setter self.set_attribute(attribute_name, value) #@property def db_get(self): """ A second convenience wrapper for the the attribute methods. It allows for the syntax obj.db.attrname = value and value = obj.db.attrname and del obj.db.attrname and all_attr = obj.db.all() (if there is no attribute named 'all', in which case that will be returned instead). """ try: return self._db_holder except AttributeError: class DbHolder(object): "Holder for allowing property access of attributes" def __init__(self, obj): object.__setattr__(self, 'obj', obj) def __getattribute__(self, attrname): obj = object.__getattribute__(self, 'obj') if attrname == 'all': # we allow for overwriting the all() method # with an attribute named 'all'. attr = obj.get_attribute("all") if attr: return attr return object.__getattribute__(self, 'all') return obj.get_attribute(attrname) def __setattr__(self, attrname, value): obj = object.__getattribute__(self, 'obj') obj.set_attribute(attrname, value) def __delattr__(self, attrname): obj = object.__getattribute__(self, 'obj') obj.del_attribute(attrname) def all(self): obj = object.__getattribute__(self, 'obj') return obj.get_all_attributes() self._db_holder = DbHolder(self) return self._db_holder #@db.setter def db_set(self, value): "Stop accidentally replacing the db object" string = "Cannot assign directly to db object! " string = "Use db.attr=value instead." raise Exception(string) #@db.deleter def db_del(self): "Stop accidental deletion." raise Exception("Cannot delete the db object!") db = property(db_get, db_set, db_del) # # NON-PERSISTENT store. If you run FULL_PERSISTENT but still # want to save something and be sure it's cleared on a server # reboot, you should use this explicitly. Otherwise there is # little point in using the non-persistent methods. # def nattr(self, attribute_name=None, value=None, delete=False): """ This is the equivalence of self.attr but for non-persistent stores. """ if attribute_name == None: # act as a list method if callable(self.ndb.all): return self.ndb.all() else: return [val for val in self.ndb.__dict__.keys() if not val.startswith['_']] elif delete == True: if hasattr(self.ndb, attribute_name): object.__delattr__(self.db, attribute_name) elif value == None: # act as a getter. if hasattr(self.ndb, attribute_name): object.__getattribute__(self.ndb, attribute_name) else: return None else: # act as a setter object.__setattr__(self.db, attribute_name, value) #@property def ndb_get(self): """ A non-persistent store (ndb: NonDataBase). Everything stored to this is guaranteed to be cleared when a server is shutdown. Works also if FULL_PERSISTENCE is active. Syntax is as for the _get_db_holder() method and property, e.g. obj.ndb.attr = value etc. """ try: return self._ndb_holder except AttributeError: class NdbHolder(object): "Holder for storing non-persistent attributes." def all(self): return [val for val in self.__dict__.keys() if not val.startswith['_']] pass self._ndb_holder = NdbHolder() return self._ndb_holder #@ndb.setter def ndb_set(self, value): "Stop accidentally replacing the db object" string = "Cannot assign directly to ndb object! " string = "Use ndb.attr=value instead." raise Exception(string) #@ndb.deleter def ndb_del(self): "Stop accidental deletion." raise Exception("Cannot delete the ndb object!") ndb = property(ndb_get, ndb_set, ndb_del)