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# -*- coding: utf-8 -*-
""" PolymorphicModel Meta Class
Please see README.rst or DOCS.rst or http://bserve.webhop.org/wiki/django_polymorphic
"""
import sys
import inspect
from django.db import models
from django.db.models.base import ModelBase
from manager 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']
###################################################################################
### 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 = self.call_superclass_new_method(model_name, bases, attrs)
# check if the model fields are all allowed
self.validate_model_fields(new_class)
# 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(model_name, 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')
# 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
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 (they are of no use),
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 ['_base_manager']: continue # let Django handle _base_manager
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 (on the bases) have no significance, they are just copies
#print >>sys.stderr,'##',self.__name__, key
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, model_name, attrs):
mgr_list = []
for key, val in attrs.items():
if not isinstance(val, models.Manager): 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=model_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)
model_module_name = attrs['__module__']
do_app_label_workaround = (meta
and model_module_name == '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
def validate_model_fields(self):
"check if all fields names are allowed (i.e. not in POLYMORPHIC_SPECIAL_Q_KWORDS)"
for f in self._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 % (self.__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'
# (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.
# TODO: investigate Django how this can be avoided
_dumpdata_command_running = False
if len(sys.argv)>1: _dumpdata_command_running = ( sys.argv[1] == 'dumpdata' )
def __getattribute__(self, name):
if name=='_default_manager':
if self._dumpdata_command_running:
frm = inspect.stack()[1] # frm[1] is caller file name, frm[3] is caller function name
if 'django/core/management/commands/dumpdata.py' 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)
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