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