# -*- coding: utf-8 -*- """ PolymorphicModel Meta Class """ from __future__ import absolute_import import inspect import os import sys from django.db import models from django.db.models.base import ModelBase from django.db.models.manager import ManagerDescriptor from .managers import PolymorphicManager from .query import PolymorphicQuerySet # PolymorphicQuerySet Q objects (and filter()) support these additional key words. # These are forbidden as field names (a descriptive exception is raised) POLYMORPHIC_SPECIAL_Q_KWORDS = ['instance_of', 'not_instance_of'] DUMPDATA_COMMAND = os.path.join('django', 'core', 'management', 'commands', 'dumpdata.py') ################################################################################### # PolymorphicModel meta class class PolymorphicModelBase(ModelBase): """ Manager inheritance is a pretty complex topic which may need more thought regarding how this should be handled for polymorphic models. In any case, we probably should propagate 'objects' and 'base_objects' from PolymorphicModel to every subclass. We also want to somehow inherit/propagate _default_manager as well, as it needs to be polymorphic. The current implementation below is an experiment to solve this problem with a very simplistic approach: We unconditionally inherit/propagate any and all managers (using _copy_to_model), as long as they are defined on polymorphic models (the others are left alone). Like Django ModelBase, we special-case _default_manager: if there are any user-defined managers, it is set to the first of these. We also require that _default_manager as well as any user defined polymorphic managers produce querysets that are derived from PolymorphicQuerySet. """ def __new__(self, model_name, bases, attrs): # print; print '###', model_name, '- bases:', bases # Workaround compatibility issue with six.with_metaclass() and custom Django model metaclasses: if not attrs and model_name == 'NewBase': return super(PolymorphicModelBase, self).__new__(self, model_name, bases, attrs) # create new model new_class = self.call_superclass_new_method(model_name, bases, attrs) # check if the model fields are all allowed self.validate_model_fields(new_class) # validate resulting default manager if not new_class._meta.abstract and not new_class._meta.swapped: self.validate_model_manager(new_class.objects, model_name, "objects") # for __init__ function of this class (monkeypatching inheritance accessors) new_class.polymorphic_super_sub_accessors_replaced = False # determine the name of the primary key field and store it into the class variable # polymorphic_primary_key_name (it is needed by query.py) for f in new_class._meta.fields: if f.primary_key and type(f) != models.OneToOneField: new_class.polymorphic_primary_key_name = f.name break return new_class @classmethod def get_first_user_defined_manager(mcs, new_class): # See if there is a manager attribute directly stored at this inheritance level. mgr_list = [] for key, val in new_class.__dict__.items(): if isinstance(val, ManagerDescriptor): val = val.manager if not isinstance(val, PolymorphicManager): continue mgr_list.append((val.creation_counter, key, val)) # if there are user defined managers, use first one as _default_manager if mgr_list: _, manager_name, manager = sorted(mgr_list)[0] # sys.stderr.write( '\n# first user defined manager for model "{model}":\n# "{mgrname}": {mgr}\n# manager model: {mgrmodel}\n\n' # .format( model=self.__name__, mgrname=manager_name, mgr=manager, mgrmodel=manager.model ) ) return manager return None @classmethod def call_superclass_new_method(self, model_name, bases, attrs): """call __new__ method of super class and return the newly created class. Also work around a limitation in Django's ModelBase.""" # There seems to be a general limitation in Django's app_label handling # regarding abstract models (in ModelBase). See issue 1 on github - TODO: propose patch for Django # We run into this problem if polymorphic.py is located in a top-level directory # which is directly in the python path. To work around this we temporarily set # app_label here for PolymorphicModel. meta = attrs.get('Meta', None) do_app_label_workaround = (meta and attrs['__module__'] == 'polymorphic' and model_name == 'PolymorphicModel' and getattr(meta, 'app_label', None) is None) if do_app_label_workaround: meta.app_label = 'poly_dummy_app_label' new_class = super(PolymorphicModelBase, self).__new__(self, model_name, bases, attrs) if do_app_label_workaround: del(meta.app_label) return new_class @classmethod def validate_model_fields(self, new_class): "check if all fields names are allowed (i.e. not in POLYMORPHIC_SPECIAL_Q_KWORDS)" for f in new_class._meta.fields: if f.name in POLYMORPHIC_SPECIAL_Q_KWORDS: e = 'PolymorphicModel: "%s" - field name "%s" is not allowed in polymorphic models' raise AssertionError(e % (new_class.__name__, f.name)) @classmethod def validate_model_manager(self, manager, model_name, manager_name): """check if the manager is derived from PolymorphicManager and its querysets from PolymorphicQuerySet - throw AssertionError if not""" if not issubclass(type(manager), PolymorphicManager): e = 'PolymorphicModel: "' + model_name + '.' + manager_name + '" manager is of type "' + type(manager).__name__ e += '", but must be a subclass of PolymorphicManager' raise AssertionError(e) if not getattr(manager, 'queryset_class', None) or not issubclass(manager.queryset_class, PolymorphicQuerySet): e = 'PolymorphicModel: "' + model_name + '.' + manager_name + '" (PolymorphicManager) has been instantiated with a queryset class which is' e += ' not a subclass of PolymorphicQuerySet (which is required)' raise AssertionError(e) return manager # hack: a small patch to Django would be a better solution. # Django's management command 'dumpdata' relies on non-polymorphic # behaviour of the _default_manager. Therefore, we catch any access to _default_manager # here and return the non-polymorphic default manager instead if we are called from 'dumpdata.py' # Otherwise, the base objects will be upcasted to polymorphic models, and be outputted as such. # (non-polymorphic default manager is 'base_objects' for polymorphic models). # This way we don't need to patch django.core.management.commands.dumpdata # for all supported Django versions. if len(sys.argv) > 1 and sys.argv[1] == 'dumpdata': # manage.py dumpdata is running def __getattribute__(self, name): if name == '_default_manager': frm = inspect.stack()[1] # frm[1] is caller file name, frm[3] is caller function name if DUMPDATA_COMMAND in frm[1]: return self.base_objects # caller_mod_name = inspect.getmodule(frm[0]).__name__ # does not work with python 2.4 # if caller_mod_name == 'django.core.management.commands.dumpdata': return super(PolymorphicModelBase, self).__getattribute__(name) # TODO: investigate Django how this can be avoided