text: # -*- coding: utf-8 -*-
  """
  Seamless Polymorphic Inheritance for Django Models
  ==================================================
  
  Please see README.rst and DOCS.rst for further information.
  
  Or on the Web:
  http://bserve.webhop.org/wiki/django_polymorphic
  http://github.com/bconstantin/django_polymorphic
  http://bitbucket.org/bconstantin/django_polymorphic
  
  Copyright:
  This code and affiliated files are (C) by Bert Constantin and individual contributors.
  Please see LICENSE and AUTHORS for more information. 
  """
  
  from pprint import pprint
  import sys
  from compatibility_tools import defaultdict
  
  from django.db import models
  from django.contrib.contenttypes.models import ContentType
  from django import VERSION as django_VERSION
  
  from base import PolymorphicModelBase
  from manager import PolymorphicManager
  from query import PolymorphicQuerySet
  from showfields import ShowFieldType
  from query_translate import translate_polymorphic_Q_object
  
   
  ###################################################################################
  ### PolymorphicModel
  
  class PolymorphicModel(models.Model):
      """
      Abstract base class that provides polymorphic behaviour
      for any model directly or indirectly derived from it.
      
      For usage instructions & examples please see documentation.
      
      PolymorphicModel declares one field for internal use (polymorphic_ctype)
      and provides a polymorphic manager as the default manager
      (and as 'objects').
      
      PolymorphicModel overrides the save() and __init__ methods.
      
      If your derived class overrides any of these methods as well, then you need
      to take care that you correctly call the method of the superclass, like:
      
          super(YourClass,self).save(*args,**kwargs)
      """
      __metaclass__ = PolymorphicModelBase
  
      # for PolymorphicModelBase, so it can tell which models are polymorphic and which are not (duck typing)
      polymorphic_model_marker = True
  
      # for PolymorphicQuery, True => an overloaded __repr__ with nicer multi-line output is used by PolymorphicQuery
      polymorphic_query_multiline_output = False
  
      class Meta:
          abstract = True
  
      # avoid ContentType related field accessor clash (an error emitted by model validation)
      # we really should use both app_label and model name, but this is only possible since Django 1.2 
      if django_VERSION[0] <= 1 and django_VERSION[1] <= 1:
          p_related_name_template = 'polymorphic_%(class)s_set'
      else:
          p_related_name_template = 'polymorphic_%(app_label)s.%(class)s_set'
      polymorphic_ctype = models.ForeignKey(ContentType, null=True, editable=False,
                                  related_name=p_related_name_template)
      
      # some applications want to know the name of the fields that are added to its models
      polymorphic_internal_model_fields = [ 'polymorphic_ctype' ]
  
      objects = PolymorphicManager()
      base_objects = models.Manager()
  
      @classmethod
      def translate_polymorphic_Q_object(self_class,q):
          return translate_polymorphic_Q_object(self_class,q)
  
      def pre_save_polymorphic(self):
          """Normally not needed.
          This function may be called manually in special use-cases. When the object
          is saved for the first time, we store its real class in polymorphic_ctype.
          When the object later is retrieved by PolymorphicQuerySet, it uses this
          field to figure out the real class of this object
          (used by PolymorphicQuerySet._get_real_instances)
          """
          if not self.polymorphic_ctype:
              self.polymorphic_ctype = ContentType.objects.get_for_model(self)
  
      def save(self, *args, **kwargs):
          """Overridden model save function which supports the polymorphism
          functionality (through pre_save_polymorphic)."""
          self.pre_save_polymorphic()
          return super(PolymorphicModel, self).save(*args, **kwargs)
  
      def get_real_instance_class(self):
          """Normally not needed.
          If a non-polymorphic manager (like base_objects) has been used to
          retrieve objects, then the real class/type of these objects may be
          determined using this method.""" 
          # the following line would be the easiest way to do this, but it produces sql queries
          #return self.polymorphic_ctype.model_class()
          # so we use the following version, which uses the CopntentType manager cache
          return ContentType.objects.get_for_id(self.polymorphic_ctype_id).model_class()
      
      def get_real_instance(self):
          """Normally not needed.
          If a non-polymorphic manager (like base_objects) has been used to
          retrieve objects, then the complete object with it's real class/type
          and all fields may be retrieved with this method.
          Each method call executes one db query (if necessary).""" 
          real_model = self.get_real_instance_class()
          if real_model == self.__class__: return self
          return real_model.objects.get(pk=self.pk)
  
  
      def __init__(self, * args, ** kwargs):
          """Replace Django's inheritance accessor member functions for our model
          (self.__class__) with our own versions.
          We monkey patch them until a patch can be added to Django
          (which would probably be very small and make all of this obsolete).
  
          If we have inheritance of the form ModelA -> ModelB ->ModelC then
          Django creates accessors like this:
          - ModelA: modelb
          - ModelB: modela_ptr, modelb, modelc
          - ModelC: modela_ptr, modelb, modelb_ptr, modelc
  
          These accessors allow Django (and everyone else) to travel up and down
          the inheritance tree for the db object at hand.
  
          The original Django accessors use our polymorphic manager.
          But they should not. So we replace them with our own accessors that use
          our appropriate base_objects manager.
          """
          super(PolymorphicModel, self).__init__(*args, ** kwargs)
  
          if self.__class__.polymorphic_super_sub_accessors_replaced: return
          self.__class__.polymorphic_super_sub_accessors_replaced = True
  
          def create_accessor_function_for_model(model, accessor_name):
              def accessor_function(self):
                  attr = model.base_objects.get(pk=self.pk)
                  return attr
              return accessor_function
  
          subclasses_and_superclasses_accessors = self._get_inheritance_relation_fields_and_models()
  
          from django.db.models.fields.related import SingleRelatedObjectDescriptor, ReverseSingleRelatedObjectDescriptor
          for name,model in subclasses_and_superclasses_accessors.iteritems():
              orig_accessor = getattr(self.__class__, name, None)
              if type(orig_accessor) in [SingleRelatedObjectDescriptor,ReverseSingleRelatedObjectDescriptor]:
                  #print >>sys.stderr, '---------- replacing',name, orig_accessor
                  setattr(self.__class__, name, property(create_accessor_function_for_model(model, name)) )
  
      def _get_inheritance_relation_fields_and_models(self):
          """helper function for __init__:
          determine names of all Django inheritance accessor member functions for type(self)"""
  
          def add_model(model, as_ptr, result):
              name = model.__name__.lower()
              if as_ptr: name+='_ptr'
              result[name] = model
  
          def add_model_if_regular(model, as_ptr, result):
              if ( issubclass(model, models.Model) and model != models.Model
                  and model != self.__class__
                  and model != PolymorphicModel ):
                  add_model(model,as_ptr,result)
  
          def add_all_super_models(model, result):
              add_model_if_regular(model, True, result)
              for b in model.__bases__:
                  add_all_super_models(b, result)
  
          def add_all_sub_models(model, result):
              for b in model.__subclasses__():
                  add_model_if_regular(b, False, result)
  
          result = {}
          add_all_super_models(self.__class__,result)
          add_all_sub_models(self.__class__,result)
          return result
  
          