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"""
Classes allowing "generic" relations through ContentType and object-id fields.
"""
from django import oldforms
from django.core.exceptions import ObjectDoesNotExist
from django.db import backend
from django.db.models import signals
from django.db.models.fields.related import RelatedField, Field, ManyToManyRel
from django.db.models.loading import get_model
from django.dispatch import dispatcher
from django.utils.functional import curry
class GenericForeignKey(object):
"""
Provides a generic relation to any object through content-type/object-id
fields.
"""
def __init__(self, ct_field="content_type", fk_field="object_id"):
self.ct_field = ct_field
self.fk_field = fk_field
def contribute_to_class(self, cls, name):
# Make sure the fields exist (these raise FieldDoesNotExist,
# which is a fine error to raise here)
self.name = name
self.model = cls
self.cache_attr = "_%s_cache" % name
# For some reason I don't totally understand, using weakrefs here doesn't work.
dispatcher.connect(self.instance_pre_init, signal=signals.pre_init, sender=cls, weak=False)
# Connect myself as the descriptor for this field
setattr(cls, name, self)
def instance_pre_init(self, signal, sender, args, kwargs):
# Handle initalizing an object with the generic FK instaed of
# content-type/object-id fields.
if kwargs.has_key(self.name):
value = kwargs.pop(self.name)
kwargs[self.ct_field] = self.get_content_type(value)
kwargs[self.fk_field] = value._get_pk_val()
def get_content_type(self, obj):
# Convenience function using get_model avoids a circular import when using this model
ContentType = get_model("contenttypes", "contenttype")
return ContentType.objects.get_for_model(obj)
def __get__(self, instance, instance_type=None):
if instance is None:
raise AttributeError, "%s must be accessed via instance" % self.name
try:
return getattr(instance, self.cache_attr)
except AttributeError:
rel_obj = None
ct = getattr(instance, self.ct_field)
if ct:
try:
rel_obj = ct.get_object_for_this_type(pk=getattr(instance, self.fk_field))
except ObjectDoesNotExist:
pass
setattr(instance, self.cache_attr, rel_obj)
return rel_obj
def __set__(self, instance, value):
if instance is None:
raise AttributeError, "%s must be accessed via instance" % self.related.opts.object_name
ct = None
fk = None
if value is not None:
ct = self.get_content_type(value)
fk = value._get_pk_val()
setattr(instance, self.ct_field, ct)
setattr(instance, self.fk_field, fk)
setattr(instance, self.cache_attr, value)
class GenericRelation(RelatedField, Field):
"""Provides an accessor to generic related objects (i.e. comments)"""
def __init__(self, to, **kwargs):
kwargs['verbose_name'] = kwargs.get('verbose_name', None)
kwargs['rel'] = GenericRel(to,
related_name=kwargs.pop('related_name', None),
limit_choices_to=kwargs.pop('limit_choices_to', None),
symmetrical=kwargs.pop('symmetrical', True))
# Override content-type/object-id field names on the related class
self.object_id_field_name = kwargs.pop("object_id_field", "object_id")
self.content_type_field_name = kwargs.pop("content_type_field", "content_type")
kwargs['blank'] = True
kwargs['editable'] = False
kwargs['serialize'] = False
Field.__init__(self, **kwargs)
def get_manipulator_field_objs(self):
choices = self.get_choices_default()
return [curry(oldforms.SelectMultipleField, size=min(max(len(choices), 5), 15), choices=choices)]
def get_choices_default(self):
return Field.get_choices(self, include_blank=False)
def flatten_data(self, follow, obj = None):
new_data = {}
if obj:
instance_ids = [instance._get_pk_val() for instance in getattr(obj, self.name).all()]
new_data[self.name] = instance_ids
return new_data
def m2m_db_table(self):
return self.rel.to._meta.db_table
def m2m_column_name(self):
return self.object_id_field_name
def m2m_reverse_name(self):
return self.object_id_field_name
def contribute_to_class(self, cls, name):
super(GenericRelation, self).contribute_to_class(cls, name)
# Save a reference to which model this class is on for future use
self.model = cls
# Add the descriptor for the m2m relation
setattr(cls, self.name, ReverseGenericRelatedObjectsDescriptor(self))
def contribute_to_related_class(self, cls, related):
pass
def set_attributes_from_rel(self):
pass
def get_internal_type(self):
return "ManyToManyField"
class ReverseGenericRelatedObjectsDescriptor(object):
"""
This class provides the functionality that makes the related-object
managers available as attributes on a model class, for fields that have
multiple "remote" values and have a GenericRelation defined in their model
(rather than having another model pointed *at* them). In the example
"article.publications", the publications attribute is a
ReverseGenericRelatedObjectsDescriptor instance.
"""
def __init__(self, field):
self.field = field
def __get__(self, instance, instance_type=None):
if instance is None:
raise AttributeError, "Manager must be accessed via instance"
# This import is done here to avoid circular import importing this module
from django.contrib.contenttypes.models import ContentType
# Dynamically create a class that subclasses the related model's
# default manager.
rel_model = self.field.rel.to
superclass = rel_model._default_manager.__class__
RelatedManager = create_generic_related_manager(superclass)
manager = RelatedManager(
model = rel_model,
instance = instance,
symmetrical = (self.field.rel.symmetrical and instance.__class__ == rel_model),
join_table = backend.quote_name(self.field.m2m_db_table()),
source_col_name = backend.quote_name(self.field.m2m_column_name()),
target_col_name = backend.quote_name(self.field.m2m_reverse_name()),
content_type = ContentType.objects.get_for_model(self.field.model),
content_type_field_name = self.field.content_type_field_name,
object_id_field_name = self.field.object_id_field_name
)
return manager
def __set__(self, instance, value):
if instance is None:
raise AttributeError, "Manager must be accessed via instance"
manager = self.__get__(instance)
manager.clear()
for obj in value:
manager.add(obj)
def create_generic_related_manager(superclass):
"""
Factory function for a manager that subclasses 'superclass' (which is a
Manager) and adds behavior for generic related objects.
"""
class GenericRelatedObjectManager(superclass):
def __init__(self, model=None, core_filters=None, instance=None, symmetrical=None,
join_table=None, source_col_name=None, target_col_name=None, content_type=None,
content_type_field_name=None, object_id_field_name=None):
super(GenericRelatedObjectManager, self).__init__()
self.core_filters = core_filters or {}
self.model = model
self.content_type = content_type
self.symmetrical = symmetrical
self.instance = instance
self.join_table = join_table
self.join_table = model._meta.db_table
self.source_col_name = source_col_name
self.target_col_name = target_col_name
self.content_type_field_name = content_type_field_name
self.object_id_field_name = object_id_field_name
self.pk_val = self.instance._get_pk_val()
def get_query_set(self):
query = {
'%s__pk' % self.content_type_field_name : self.content_type.id,
'%s__exact' % self.object_id_field_name : self.pk_val,
}
return superclass.get_query_set(self).filter(**query)
def add(self, *objs):
for obj in objs:
setattr(obj, self.content_type_field_name, self.content_type)
setattr(obj, self.object_id_field_name, self.pk_val)
obj.save()
add.alters_data = True
def remove(self, *objs):
for obj in objs:
obj.delete()
remove.alters_data = True
def clear(self):
for obj in self.all():
obj.delete()
clear.alters_data = True
def create(self, **kwargs):
kwargs[self.content_type_field_name] = self.content_type
kwargs[self.object_id_field_name] = self.pk_val
obj = self.model(**kwargs)
obj.save()
return obj
create.alters_data = True
return GenericRelatedObjectManager
class GenericRel(ManyToManyRel):
def __init__(self, to, related_name=None, limit_choices_to=None, symmetrical=True):
self.to = to
self.num_in_admin = 0
self.related_name = related_name
self.filter_interface = None
self.limit_choices_to = limit_choices_to or {}
self.edit_inline = False
self.raw_id_admin = False
self.symmetrical = symmetrical
self.multiple = True
assert not (self.raw_id_admin and self.filter_interface), \
"Generic relations may not use both raw_id_admin and filter_interface"
|
