638 lines
28 KiB
Python
638 lines
28 KiB
Python
# -*- coding: utf-8 -*-
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"""
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Fully Polymorphic Django Models
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===============================
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Please see the examples and documentation here:
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http://bserve.webhop.org/wiki/django_polymorphic
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or in the included README.rst and DOCS.rst files.
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Copyright:
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This code and affiliated files are (C) by
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Bert Constantin and the individual contributors.
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Please see LICENSE and AUTHORS for more information.
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"""
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from django.db import models
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from django.db.models.base import ModelBase
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from django.db.models.query import QuerySet
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from collections import defaultdict
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from pprint import pprint
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from django.contrib.contenttypes.models import ContentType
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# chunk-size: maximum number of objects requested per db-request
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# by the polymorphic queryset.iterator() implementation
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Polymorphic_QuerySet_objects_per_request = 100
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###################################################################################
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### PolymorphicManager
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class PolymorphicManager(models.Manager):
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"""
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Manager for PolymorphicModel
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Usually not explicitly needed, except if a custom manager or
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a custom queryset class is to be used.
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"""
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use_for_related_fields = True
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def __init__(self, queryset_class=None, *args, **kwrags):
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if not queryset_class: self.queryset_class = PolymorphicQuerySet
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else: self.queryset_class = queryset_class
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super(PolymorphicManager, self).__init__(*args, **kwrags)
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def get_query_set(self):
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return self.queryset_class(self.model)
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# Proxy all unknown method calls to the queryset, so that its members are
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# directly accessible from PolymorphicModel.objects.
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# The advantage is that not yet known member functions of derived querysets will be proxied as well.
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# We exclude any special functions (__) from this automatic proxying.
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def __getattr__(self, name):
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if name.startswith('__'): return super(PolymorphicManager, self).__getattr__(self, name)
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return getattr(self.get_query_set(), name)
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def __unicode__(self):
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return self.__class__.__name__ + ' (PolymorphicManager) using ' + self.queryset_class.__name__
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###################################################################################
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### PolymorphicQuerySet
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class PolymorphicQuerySet(QuerySet):
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"""
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QuerySet for PolymorphicModel
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Contains the core functionality for PolymorphicModel
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Usually not explicitly needed, except if a custom queryset class
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is to be used.
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"""
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def instance_of(self, *args):
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return self.filter(instance_of=args)
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def not_instance_of(self, *args):
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return self.filter(not_instance_of=args)
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def _filter_or_exclude(self, negate, *args, **kwargs):
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_translate_polymorphic_filter_specs_in_args(self.model, args)
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additional_args = _translate_polymorphic_filter_specs_in_kwargs(self.model, kwargs)
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return super(PolymorphicQuerySet, self)._filter_or_exclude(negate, *(list(args) + additional_args), **kwargs)
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def _get_real_instances(self, base_result_objects):
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"""
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Polymorphic object loader
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Does the same as:
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return [ o.get_real_instance() for o in base_result_objects ]
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The list base_result_objects contains the objects from the executed
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base class query. The class of all of them is self.model (our base model).
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Some, many or all of these objects were not created and stored as
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class self.model, but as a class derived from self.model. We want to fetch
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these objects from the db so we can return them just as they were saved.
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We identify these objects by looking at o.polymorphic_ctype, which specifies
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the real class of these objects (the class at the time they were saved).
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First, we sort the result objects in base_result_objects for their
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subclass (from o.polymorphic_ctype), and then we execute one db query per
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subclass of objects. Finally we re-sort the resulting objects into the
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correct order and return them as a list.
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"""
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ordered_id_list = [] # list of ids of result-objects in correct order
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results = {} # polymorphic dict of result-objects, keyed with their id (no order)
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# dict contains one entry for the different model types occurring in result,
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# in the format idlist_per_model['applabel.modelname']=[list-of-ids-for-this-model]
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idlist_per_model = defaultdict(list)
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# - sort base_result_object ids into idlist_per_model lists, depending on their real class;
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# - also record the correct result order in "ordered_id_list"
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# - store objects that already have the correct class into "results"
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self_model_content_type_id = ContentType.objects.get_for_model(self.model).pk
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for base_object in base_result_objects:
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ordered_id_list.append(base_object.id)
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# this object is not a derived object and already the real instance => store it right away
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if (base_object.polymorphic_ctype_id == self_model_content_type_id):
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results[base_object.id] = base_object
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# this object is derived and its real instance needs to be retrieved
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# => store it's id into the bin for this model type
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else:
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idlist_per_model[base_object.get_real_instance_class()].append(base_object.id)
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# for each model in "idlist_per_model" request its objects (the full model)
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# from the db and store them in results[]
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for modelclass, idlist in idlist_per_model.items():
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qs = modelclass.base_objects.filter(id__in=idlist)
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# copy select related configuration to new qs
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# TODO: this does not seem to copy the complete sel_rel-config (field names etc.)
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self.dup_select_related(qs)
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# TODO: defer(), only() and annotate(): support for these would be around here
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for o in qs: results[o.id] = o
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# re-create correct order and return result list
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resultlist = [ results[ordered_id] for ordered_id in ordered_id_list if ordered_id in results ]
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return resultlist
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def iterator(self):
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"""
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This function does the same as:
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base_result_objects=list(super(PolymorphicQuerySet, self).iterator())
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real_results=self._get_get_real_instances(base_result_objects)
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for o in real_results: yield o
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but it requests the objects in chunks from the database,
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with Polymorphic_QuerySet_objects_per_request per chunk
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"""
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base_iter = super(PolymorphicQuerySet, self).iterator()
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while True:
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base_result_objects = []
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reached_end = False
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for i in range(Polymorphic_QuerySet_objects_per_request):
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try: base_result_objects.append(base_iter.next())
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except StopIteration:
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reached_end = True
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break
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real_results = self._get_real_instances(base_result_objects)
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for o in real_results:
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yield o
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if reached_end: raise StopIteration
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# these queryset functions are not yet supported
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def defer(self, *args, **kwargs): raise NotImplementedError
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def only(self, *args, **kwargs): raise NotImplementedError
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def aggregate(self, *args, **kwargs): raise NotImplementedError
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def annotate(self, *args, **kwargs): raise NotImplementedError
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def __repr__(self):
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result = [ repr(o) for o in self.all() ]
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return '[ ' + ',\n '.join(result) + ' ]'
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###################################################################################
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### PolymorphicQuerySet support functions
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# These functions implement the additional filter- and Q-object functionality.
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# They form a kind of small framework for easily adding more
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# functionality to filters and Q objects.
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# Probably a more general queryset enhancement class could be made out them.
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def _translate_polymorphic_filter_specs_in_kwargs(queryset_model, kwargs):
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"""
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Translate the keyword argument list for PolymorphicQuerySet.filter()
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Any kwargs with special polymorphic functionality are replaced in the kwargs
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dict with their vanilla django equivalents.
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For some kwargs a direct replacement is not possible, as a Q object is needed
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instead to implement the required functionality. In these cases the kwarg is
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deleted from the kwargs dict and a Q object is added to the return list.
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Modifies: kwargs dict
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Returns: a list of non-keyword-arguments (Q objects) to be added to the filter() query.
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"""
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additional_args = []
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for field_path, val in kwargs.items():
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# normal filter expression => ignore
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new_expr = _translate_polymorphic_filter_spec(queryset_model, field_path, val)
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if type(new_expr) == tuple:
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# replace kwargs element
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del(kwargs[field_path])
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kwargs[new_expr[0]] = new_expr[1]
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elif isinstance(new_expr, models.Q):
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del(kwargs[field_path])
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additional_args.append(new_expr)
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return additional_args
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def _translate_polymorphic_filter_specs_in_args(queryset_model, args):
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"""
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Translate the non-keyword argument list for PolymorphicQuerySet.filter()
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In the args list, we replace all kwargs to Q-objects that contain special
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polymorphic functionality with their vanilla django equivalents.
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We traverse the Q object tree for this (which is simple).
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Modifies: args list
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"""
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def tree_node_correct_field_specs(node):
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" process all children of this Q node "
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for i in range(len(node.children)):
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child = node.children[i]
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if type(child) == tuple:
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# this Q object child is a tuple => a kwarg like Q( instance_of=ModelB )
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key, val = child
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new_expr = _translate_polymorphic_filter_spec(queryset_model, key, val)
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if new_expr:
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node.children[i] = new_expr
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else:
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# this Q object child is another Q object, recursively process this as well
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tree_node_correct_field_specs(child)
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for q in args:
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if isinstance(q, models.Q):
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tree_node_correct_field_specs(q)
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def _translate_polymorphic_filter_spec(queryset_model, field_path, field_val):
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"""
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Translate a keyword argument (field_path=field_val), as used for
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PolymorphicQuerySet.filter()-like functions (and Q objects).
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A kwarg with special polymorphic functionality is translated into
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its vanilla django equivalent, which is returned, either as tuple
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(field_path, field_val) or as Q object.
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Returns: kwarg tuple or Q object or None (if no change is required)
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"""
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# handle instance_of expressions or alternatively,
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# if this is a normal Django filter expression, return None
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if field_path == 'instance_of':
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return _create_model_filter_Q(field_val)
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elif field_path == 'not_instance_of':
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return _create_model_filter_Q(field_val, not_instance_of=True)
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elif not '___' in field_path:
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return None #no change
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# filter expression contains '___' (i.e. filter for polymorphic field)
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# => get the model class specified in the filter expression
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newpath = _translate_polymorphic_field_path(queryset_model, field_path)
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return (newpath, field_val)
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def _translate_polymorphic_field_path(queryset_model, field_path):
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"""
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Translate a field path from keyword argument, as used for
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PolymorphicQuerySet.filter()-like functions (and Q objects).
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E.g.: ModelC___field3 is translated into modela__modelb__modelc__field3
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Returns: translated path
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"""
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classname, sep, pure_field_path = field_path.partition('___')
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assert sep == '___'
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if '__' in classname:
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# the user has app label prepended to class name via __ => use Django's get_model function
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appname, sep, classname = classname.partition('__')
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model = models.get_model(appname, classname)
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assert model, 'PolymorphicModel: model %s (in app %s) not found!' % (model.__name__, appname)
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if not issubclass(model, queryset_model):
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e = 'PolymorphicModel: queryset filter error: "' + model.__name__ + '" is not derived from "' + queryset_model.__name__ + '"'
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raise AssertionError(e)
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else:
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# the user has only given us the class name via __
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# => select the model from the sub models of the queryset base model
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# function to collect all sub-models, this should be optimized (cached)
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def add_all_sub_models(model, result):
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if issubclass(model, models.Model) and model != models.Model:
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# model name is occurring twice in submodel inheritance tree => Error
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if model.__name__ in result and model != result[model.__name__]:
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assert model, 'PolymorphicModel: model name is ambiguous: %s.%s, %s.%s!' % (
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model._meta.app_label, model.__name__,
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result[model.__name__]._meta.app_label, result[model.__name__].__name__)
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result[model.__name__] = model
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for b in model.__subclasses__():
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add_all_sub_models(b, result)
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submodels = {}
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add_all_sub_models(queryset_model, submodels)
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model = submodels.get(classname, None)
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assert model, 'PolymorphicModel: model %s not found (not a subclass of %s)!' % (model.__name__, queryset_model.__name__)
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# create new field path for expressions, e.g. for baseclass=ModelA, myclass=ModelC
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# 'modelb__modelc" is returned
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def _create_base_path(baseclass, myclass):
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bases = myclass.__bases__
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for b in bases:
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if b == baseclass:
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return myclass.__name__.lower()
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path = _create_base_path(baseclass, b)
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if path: return path + '__' + myclass.__name__.lower()
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return ''
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basepath = _create_base_path(queryset_model, model)
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newpath = basepath + '__' if basepath else ''
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newpath += pure_field_path
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return newpath
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def _create_model_filter_Q(modellist, not_instance_of=False):
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"""
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Helper function for instance_of / not_instance_of
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Creates and returns a Q object that filters for the models in modellist,
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including all subclasses of these models (as we want to do the same
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as pythons isinstance() ).
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.
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We recursively collect all __subclasses__(), create a Q filter for each,
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and or-combine these Q objects. This could be done much more
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efficiently however (regarding the resulting sql), should an optimization
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be needed.
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"""
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if not modellist: return None
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from django.db.models import Q
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if type(modellist) != list and type(modellist) != tuple:
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if issubclass(modellist, PolymorphicModel):
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modellist = [modellist]
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else:
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assert False, 'PolymorphicModel: instance_of expects a list of models or a single model'
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def q_class_with_subclasses(model):
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q = Q(polymorphic_ctype=ContentType.objects.get_for_model(model))
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for subclass in model.__subclasses__():
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q = q | q_class_with_subclasses(subclass)
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return q
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qlist = [ q_class_with_subclasses(m) for m in modellist ]
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q_ored = reduce(lambda a, b: a | b, qlist)
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if not_instance_of: q_ored = ~q_ored
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return q_ored
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###################################################################################
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### PolymorphicModel meta class
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class PolymorphicModelBase(ModelBase):
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"""
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Manager inheritance is a pretty complex topic which may need
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more thought regarding how this should be handled for polymorphic
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models.
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In any case, we probably should propagate 'objects' and 'base_objects'
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from PolymorphicModel to every subclass. We also want to somehow
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inherit/propagate _default_manager as well, as it needs to be polymorphic.
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The current implementation below is an experiment to solve this
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problem with a very simplistic approach: We unconditionally
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inherit/propagate any and all managers (using _copy_to_model),
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as long as they are defined on polymorphic models
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(the others are left alone).
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Like Django ModelBase, we special-case _default_manager:
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if there are any user-defined managers, it is set to the first of these.
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We also require that _default_manager as well as any user defined
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polymorphic managers produce querysets that are derived from
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PolymorphicQuerySet.
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"""
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def __new__(self, model_name, bases, attrs):
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#print; print '###', model_name, '- bases:', bases
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# create new model
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new_class = super(PolymorphicModelBase, self).__new__(self, model_name, bases, attrs)
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# create list of all managers to be inherited from the base classes
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inherited_managers = new_class.get_inherited_managers(attrs)
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# add the managers to the new model
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for source_name, mgr_name, manager in inherited_managers:
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#print '** add inherited manager from model %s, manager %s, %s' % (source_name, mgr_name, manager.__class__.__name__)
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new_manager = manager._copy_to_model(new_class)
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new_class.add_to_class(mgr_name, new_manager)
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# get first user defined manager; if there is one, make it the _default_manager
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user_manager = self.get_first_user_defined_manager(attrs)
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if user_manager:
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def_mgr = user_manager._copy_to_model(new_class)
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#print '## add default manager', type(def_mgr)
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new_class.add_to_class('_default_manager', def_mgr)
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new_class._default_manager._inherited = False # the default mgr was defined by the user, not inherited
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# validate resulting default manager
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self.validate_model_manager(new_class._default_manager, model_name, '_default_manager')
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return new_class
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def get_inherited_managers(self, attrs):
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"""
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Return list of all managers to be inherited/propagated from the base classes;
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use correct mro, only use managers with _inherited==False,
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skip managers that are overwritten by the user with same-named class attributes (in attrs)
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"""
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add_managers = []; add_managers_keys = set()
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for base in self.__mro__[1:]:
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if not issubclass(base, models.Model): continue
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if not getattr(base, 'polymorphic_model_marker', None): continue # leave managers of non-polym. models alone
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for key, manager in base.__dict__.items():
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if type(manager) == models.manager.ManagerDescriptor: manager = manager.manager
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if not isinstance(manager, models.Manager): continue
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if key in attrs: continue
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if key in add_managers_keys: continue # manager with that name already added, skip
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if manager._inherited: continue # inherited managers have no significance, they are just copies
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if isinstance(manager, PolymorphicManager): # validate any inherited polymorphic managers
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self.validate_model_manager(manager, self.__name__, key)
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add_managers.append((base.__name__, key, manager))
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add_managers_keys.add(key)
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return add_managers
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@classmethod
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def get_first_user_defined_manager(self, attrs):
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mgr_list = []
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for key, val in attrs.items():
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if not isinstance(val, models.Manager): continue
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mgr_list.append((val.creation_counter, val))
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# if there are user defined managers, use first one as _default_manager
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if mgr_list: #
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_, manager = sorted(mgr_list)[0]
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return manager
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return None
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@classmethod
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def validate_model_manager(self, manager, model_name, manager_name):
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"""check if the manager is derived from PolymorphicManager
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and its querysets from PolymorphicQuerySet - throw AssertionError if not"""
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if not issubclass(type(manager), PolymorphicManager):
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e = 'PolymorphicModel: "' + model_name + '.' + manager_name + '" manager is of type "' + type(manager).__name__
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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__ + ': ').ljust(17) + 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 + '>'
|
|
|