# -*- coding: utf-8 -*- """ Fully Polymorphic Django Models =============================== Please see the examples and documentation here: http://bserve.webhop.org/wiki/django_polymorphic or in the included README.rst and DOCS.rst files. Copyright: This code and affiliated files are (C) by Bert Constantin and individual contributors. Please see LICENSE and AUTHORS for more information. """ from django.db import models from django.db.models.base import ModelBase from django.db.models.query import QuerySet from collections import defaultdict from pprint import pprint from django.contrib.contenttypes.models import ContentType import sys # chunk-size: maximum number of objects requested per db-request # by the polymorphic queryset.iterator() implementation Polymorphic_QuerySet_objects_per_request = 100 ################################################################################### ### PolymorphicManager class PolymorphicManager(models.Manager): """ Manager for PolymorphicModel Usually not explicitly needed, except if a custom manager or a custom queryset class is to be used. """ use_for_related_fields = True def __init__(self, queryset_class=None, *args, **kwrags): if not queryset_class: self.queryset_class = PolymorphicQuerySet else: self.queryset_class = queryset_class super(PolymorphicManager, self).__init__(*args, **kwrags) def get_query_set(self): return self.queryset_class(self.model) # Proxy all unknown method calls to the queryset, so that its members are # directly accessible as PolymorphicModel.objects.* # The advantage is that not yet known member functions of derived querysets will be proxied as well. # We exclude any special functions (__) from this automatic proxying. def __getattr__(self, name): if name.startswith('__'): return super(PolymorphicManager, self).__getattr__(self, name) return getattr(self.get_query_set(), name) def __unicode__(self): return self.__class__.__name__ + ' (PolymorphicManager) using ' + self.queryset_class.__name__ ################################################################################### ### PolymorphicQuerySet class PolymorphicQuerySet(QuerySet): """ QuerySet for PolymorphicModel Contains the core functionality for PolymorphicModel Usually not explicitly needed, except if a custom queryset class is to be used. """ def instance_of(self, *args): return self.filter(instance_of=args) def not_instance_of(self, *args): return self.filter(not_instance_of=args) def _filter_or_exclude(self, negate, *args, **kwargs): _translate_polymorphic_filter_specs_in_args(self.model, args) additional_args = _translate_polymorphic_filter_specs_in_kwargs(self.model, kwargs) return super(PolymorphicQuerySet, self)._filter_or_exclude(negate, *(list(args) + additional_args), **kwargs) def _get_real_instances(self, base_result_objects): """ Polymorphic object loader Does the same as: return [ o.get_real_instance() for o in base_result_objects ] The list base_result_objects contains the objects from the executed base class query. The class of all of them is self.model (our base model). Some, many or all of these objects were not created and stored as class self.model, but as a class derived from self.model. We want to fetch these objects from the db so we can return them just as they were saved. We identify these objects by looking at o.polymorphic_ctype, which specifies the real class of these objects (the class at the time they were saved). First, we sort the result objects in base_result_objects for their subclass (from o.polymorphic_ctype), and then we execute one db query per subclass of objects. Finally we re-sort the resulting objects into the correct order and return them as a list. """ ordered_id_list = [] # list of ids of result-objects in correct order results = {} # polymorphic dict of result-objects, keyed with their id (no order) # dict contains one entry per unique model type occurring in result, # in the format idlist_per_model[modelclass]=[list-of-object-ids] idlist_per_model = defaultdict(list) # - sort base_result_object ids into idlist_per_model lists, depending on their real class; # - also record the correct result order in "ordered_id_list" # - store objects that already have the correct class into "results" self_model_content_type_id = ContentType.objects.get_for_model(self.model).pk for base_object in base_result_objects: ordered_id_list.append(base_object.id) # this object is not a derived object and already the real instance => store it right away if (base_object.polymorphic_ctype_id == self_model_content_type_id): results[base_object.id] = base_object # this object is derived and its real instance needs to be retrieved # => store it's id into the bin for this model type else: idlist_per_model[base_object.get_real_instance_class()].append(base_object.id) # for each model in "idlist_per_model" request its objects (the full model) # from the db and store them in results[] for modelclass, idlist in idlist_per_model.items(): qs = modelclass.base_objects.filter(id__in=idlist) # copy select related configuration to new qs # TODO: this does not seem to copy the complete sel_rel-config (field names etc.) self.dup_select_related(qs) # TODO: defer(), only() and annotate(): support for these would be around here for o in qs: results[o.id] = o # re-create correct order and return result list resultlist = [ results[ordered_id] for ordered_id in ordered_id_list if ordered_id in results ] return resultlist def iterator(self): """ This function does the same as: base_result_objects=list(super(PolymorphicQuerySet, self).iterator()) real_results=self._get_get_real_instances(base_result_objects) for o in real_results: yield o but it requests the objects in chunks from the database, with Polymorphic_QuerySet_objects_per_request per chunk """ base_iter = super(PolymorphicQuerySet, self).iterator() while True: base_result_objects = [] reached_end = False for i in range(Polymorphic_QuerySet_objects_per_request): try: base_result_objects.append(base_iter.next()) except StopIteration: reached_end = True break real_results = self._get_real_instances(base_result_objects) for o in real_results: yield o if reached_end: raise StopIteration # these queryset functions are not yet supported def defer(self, *args, **kwargs): raise NotImplementedError def only(self, *args, **kwargs): raise NotImplementedError def aggregate(self, *args, **kwargs): raise NotImplementedError def annotate(self, *args, **kwargs): raise NotImplementedError def __repr__(self): result = [ repr(o) for o in self.all() ] return '[ ' + ',\n '.join(result) + ' ]' ################################################################################### ### PolymorphicQuerySet support functions # These functions implement the additional filter- and Q-object functionality. # They form a kind of small framework for easily adding more # functionality to filters and Q objects. # Probably a more general queryset enhancement class could be made out them. def _translate_polymorphic_filter_specs_in_kwargs(queryset_model, kwargs): """ Translate the keyword argument list for PolymorphicQuerySet.filter() Any kwargs with special polymorphic functionality are replaced in the kwargs dict with their vanilla django equivalents. For some kwargs a direct replacement is not possible, as a Q object is needed instead to implement the required functionality. In these cases the kwarg is deleted from the kwargs dict and a Q object is added to the return list. Modifies: kwargs dict Returns: a list of non-keyword-arguments (Q objects) to be added to the filter() query. """ additional_args = [] for field_path, val in kwargs.items(): # normal filter expression => ignore new_expr = _translate_polymorphic_filter_spec(queryset_model, field_path, val) if type(new_expr) == tuple: # replace kwargs element del(kwargs[field_path]) kwargs[new_expr[0]] = new_expr[1] elif isinstance(new_expr, models.Q): del(kwargs[field_path]) additional_args.append(new_expr) return additional_args def _translate_polymorphic_filter_specs_in_args(queryset_model, args): """ Translate the non-keyword argument list for PolymorphicQuerySet.filter() In the args list, we replace all kwargs to Q-objects that contain special polymorphic functionality with their vanilla django equivalents. We traverse the Q object tree for this (which is simple). Modifies: args list """ def tree_node_correct_field_specs(node): " process all children of this Q node " for i in range(len(node.children)): child = node.children[i] if type(child) == tuple: # this Q object child is a tuple => a kwarg like Q( instance_of=ModelB ) key, val = child new_expr = _translate_polymorphic_filter_spec(queryset_model, key, val) if new_expr: node.children[i] = new_expr else: # this Q object child is another Q object, recursively process this as well tree_node_correct_field_specs(child) for q in args: if isinstance(q, models.Q): tree_node_correct_field_specs(q) def _translate_polymorphic_filter_spec(queryset_model, field_path, field_val): """ Translate a keyword argument (field_path=field_val), as used for PolymorphicQuerySet.filter()-like functions (and Q objects). A kwarg with special polymorphic functionality is translated into its vanilla django equivalent, which is returned, either as tuple (field_path, field_val) or as Q object. Returns: kwarg tuple or Q object or None (if no change is required) """ # handle instance_of expressions or alternatively, # if this is a normal Django filter expression, return None if field_path == 'instance_of': return _create_model_filter_Q(field_val) elif field_path == 'not_instance_of': return _create_model_filter_Q(field_val, not_instance_of=True) elif not '___' in field_path: return None #no change # filter expression contains '___' (i.e. filter for polymorphic field) # => get the model class specified in the filter expression newpath = _translate_polymorphic_field_path(queryset_model, field_path) return (newpath, field_val) def _translate_polymorphic_field_path(queryset_model, field_path): """ Translate a field path from keyword argument, as used for PolymorphicQuerySet.filter()-like functions (and Q objects). E.g.: ModelC___field3 is translated into modela__modelb__modelc__field3 Returns: translated path """ classname, sep, pure_field_path = field_path.partition('___') assert sep == '___' if '__' in classname: # the user has app label prepended to class name via __ => use Django's get_model function appname, sep, classname = classname.partition('__') model = models.get_model(appname, classname) assert model, 'PolymorphicModel: model %s (in app %s) not found!' % (model.__name__, appname) if not issubclass(model, queryset_model): e = 'PolymorphicModel: queryset filter error: "' + model.__name__ + '" is not derived from "' + queryset_model.__name__ + '"' raise AssertionError(e) else: # the user has only given us the class name via __ # => select the model from the sub models of the queryset base model # function to collect all sub-models, this should be optimized (cached) def add_all_sub_models(model, result): if issubclass(model, models.Model) and model != models.Model: # model name is occurring twice in submodel inheritance tree => Error if model.__name__ in result and model != result[model.__name__]: e = 'PolymorphicModel: model name alone is ambiguous: %s.%s and %s.%s!\n' e += 'In this case, please use the syntax: applabel__ModelName___field' assert model, e % ( model._meta.app_label, model.__name__, result[model.__name__]._meta.app_label, result[model.__name__].__name__) result[model.__name__] = model for b in model.__subclasses__(): add_all_sub_models(b, result) submodels = {} add_all_sub_models(queryset_model, submodels) model = submodels.get(classname, None) assert model, 'PolymorphicModel: model %s not found (not a subclass of %s)!' % (model.__name__, queryset_model.__name__) # create new field path for expressions, e.g. for baseclass=ModelA, myclass=ModelC # 'modelb__modelc" is returned def _create_base_path(baseclass, myclass): bases = myclass.__bases__ for b in bases: if b == baseclass: return myclass.__name__.lower() path = _create_base_path(baseclass, b) if path: return path + '__' + myclass.__name__.lower() return '' basepath = _create_base_path(queryset_model, model) newpath = basepath + '__' if basepath else '' newpath += pure_field_path return newpath def _create_model_filter_Q(modellist, not_instance_of=False): """ Helper function for instance_of / not_instance_of Creates and returns a Q object that filters for the models in modellist, including all subclasses of these models (as we want to do the same as pythons isinstance() ). . We recursively collect all __subclasses__(), create a Q filter for each, and or-combine these Q objects. This could be done much more efficiently however (regarding the resulting sql), should an optimization be needed. """ if not modellist: return None from django.db.models import Q if type(modellist) != list and type(modellist) != tuple: if issubclass(modellist, PolymorphicModel): modellist = [modellist] else: assert False, 'PolymorphicModel: instance_of expects a list of models or a single model' def q_class_with_subclasses(model): q = Q(polymorphic_ctype=ContentType.objects.get_for_model(model)) for subclass in model.__subclasses__(): q = q | q_class_with_subclasses(subclass) return q qlist = [ q_class_with_subclasses(m) for m in modellist ] q_ored = reduce(lambda a, b: a | b, qlist) if not_instance_of: q_ored = ~q_ored return q_ored ################################################################################### ### 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 # create new model new_class = super(PolymorphicModelBase, self).__new__(self, model_name, bases, attrs) # create list of all managers to be inherited from the base classes inherited_managers = new_class.get_inherited_managers(attrs) # add the managers to the new model for source_name, mgr_name, manager in inherited_managers: #print '** add inherited manager from model %s, manager %s, %s' % (source_name, mgr_name, manager.__class__.__name__) new_manager = manager._copy_to_model(new_class) new_class.add_to_class(mgr_name, new_manager) # get first user defined manager; if there is one, make it the _default_manager user_manager = self.get_first_user_defined_manager(attrs) if user_manager: def_mgr = user_manager._copy_to_model(new_class) #print '## add default manager', type(def_mgr) new_class.add_to_class('_default_manager', def_mgr) new_class._default_manager._inherited = False # the default mgr was defined by the user, not inherited # validate resulting default manager self.validate_model_manager(new_class._default_manager, model_name, '_default_manager') return new_class def get_inherited_managers(self, attrs): """ Return list of all managers to be inherited/propagated from the base classes; use correct mro, only use managers with _inherited==False, skip managers that are overwritten by the user with same-named class attributes (in attrs) """ add_managers = []; add_managers_keys = set() for base in self.__mro__[1:]: if not issubclass(base, models.Model): continue if not getattr(base, 'polymorphic_model_marker', None): continue # leave managers of non-polym. models alone for key, manager in base.__dict__.items(): if type(manager) == models.manager.ManagerDescriptor: manager = manager.manager if not isinstance(manager, models.Manager): continue if key in attrs: continue if key in add_managers_keys: continue # manager with that name already added, skip if manager._inherited: continue # inherited managers have no significance, they are just copies if isinstance(manager, PolymorphicManager): # validate any inherited polymorphic managers self.validate_model_manager(manager, self.__name__, key) add_managers.append((base.__name__, key, manager)) add_managers_keys.add(key) return add_managers @classmethod def get_first_user_defined_manager(self, attrs): mgr_list = [] for key, val in attrs.items(): if not isinstance(val, models.Manager): continue mgr_list.append((val.creation_counter, val)) # if there are user defined managers, use first one as _default_manager if mgr_list: # _, manager = sorted(mgr_list)[0] return manager return None @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 ################################################################################### ### 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() method. If your derived class overrides save() as well, then you need to take care that you correctly call the save() method of the superclass, like: super(YourClass,self).save(*args,**kwargs) """ __metaclass__ = PolymorphicModelBase polymorphic_model_marker = True # for PolymorphicModelBase class Meta: abstract = True polymorphic_ctype = models.ForeignKey(ContentType, null=True, editable=False) # 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() 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(id=self.id) # Hack: # For base model back reference fields (like basemodel_ptr), # Django definitely must =not= use our polymorphic manager/queryset. # For now, we catch objects attribute access here and handle back reference fields manually. # This problem is triggered by delete(), like here: # django.db.models.base._collect_sub_objects: parent_obj = getattr(self, link.name) # TODO: investigate Django how this can be avoided def __getattribute__(self, name): if name != '__class__': #if name.endswith('_ptr_cache'): # unclear if this should be handled as well if name.endswith('_ptr'): name = name[:-4] model = self.__class__.sub_and_superclass_dict.get(name, None) if model: id = super(PolymorphicModel, self).__getattribute__('id') attr = model.base_objects.get(id=id) return attr return super(PolymorphicModel, self).__getattribute__(name) # support for __getattribute__ hack: create sub_and_superclass_dict, # containing all model attribute names we need to intercept # (do this once here instead of in __getattribute__ every time) def __init__(self, *args, **kwargs): if not getattr(self.__class__, 'sub_and_superclass_dict', None): def add_all_base_models(model, result): if issubclass(model, models.Model) and model != models.Model: result[model.__name__.lower()] = model for b in model.__bases__: add_all_base_models(b, result) def add_all_sub_models(model, result): if issubclass(model, models.Model) and model != models.Model: result[model.__name__.lower()] = model for b in model.__subclasses__(): add_all_sub_models(b, result) result = {} add_all_base_models(self.__class__, result) add_all_sub_models(self.__class__, result) self.__class__.sub_and_superclass_dict = result super(PolymorphicModel, self).__init__(*args, **kwargs) def __repr__(self): out = self.__class__.__name__ + ': id %d, ' % (self.id or - 1); last = self._meta.fields[-1] for f in self._meta.fields: if f.name in [ 'id' ] + self.polymorphic_internal_model_fields or 'ptr' in f.name: continue out += f.name + ' (' + type(f).__name__ + ')' if f != last: out += ', ' return '<' + out + '>' class ShowFields(object): """ mixin that shows the object's class, it's fields and field contents """ def __repr__(self): out = 'id %d, ' % (self.id); last = self._meta.fields[-1] for f in self._meta.fields: if f.name in [ 'id' ] + self.polymorphic_internal_model_fields or 'ptr' in f.name: continue out += f.name if isinstance(f, (models.ForeignKey)): o = getattr(self, f.name) out += ': "' + ('None' if o == None else o.__class__.__name__) + '"' else: out += ': "' + getattr(self, f.name) + '"' if f != last: out += ', ' return '<' + (self.__class__.__name__ + ': ') + out + '>' class ShowFieldsAndTypes(object): """ like ShowFields, but also show field types """ def __repr__(self): out = 'id %d, ' % (self.id); last = self._meta.fields[-1] for f in self._meta.fields: if f.name in [ 'id' ] + self.polymorphic_internal_model_fields or 'ptr' in f.name: continue out += f.name + ' (' + type(f).__name__ + ')' if isinstance(f, (models.ForeignKey)): o = getattr(self, f.name) out += ': "' + ('None' if o == None else o.__class__.__name__) + '"' else: out += ': "' + getattr(self, f.name) + '"' if f != last: out += ', ' return '<' + self.__class__.__name__ + ': ' + out + '>'