evennia/src/typeclasses/models.py

"""
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 dhango 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 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 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, value):
        "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.
        """
        return [attr for attr in self.objattribute_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)