以前，当我想递归地克隆对象时，我遇到了问题。
我知道克隆对象的简单方法是这样的：
obj = Foo.objects.get(pk=<some_existing_pk>)
obj.pk = None
obj.save()
但是，我想做得更深入。例如，我有一个models.py
class Post(TimeStampedModel):
author = models.ForeignKey(User, related_name='posts',
on_delete=models.CASCADE)
title = models.CharField(_('Title'), max_length=200)
content = models.TextField(_('Content'))
...
class Comment(TimeStampedModel):
author = models.ForeignKey(User, related_name='comments',
on_delete=models.CASCADE)
post = models.ForeignKey(Post, on_delete=models.CASCADE)
comment = models.TextField(_('Comment'))
...
class CommentAttribute(TimeStampedModel):
comment = models.OneToOneField(Comment, related_name='comment_attribute',
on_delete=models.CASCADE)
is_bookmark = models.BooleanField(default=False)
...
class PostComment(TimeStampedModel):
post = models.ForeignKey(Post, related_name='post_comments',
on_delete=models.CASCADE)
comments = models.ManyToManyField(Comment)
...
当我从以下位置克隆父对象时Post，孩子的对象就像Comment, CommentAttribute and PostComment也将通过以下新克隆来克隆Post对象。
子模型是动态地。因此，我想通过创建对象克隆器之类的工具来使其变得简单。
下面的代码片段是我所做的；
from django.db.utils import IntegrityError
class ObjectCloner(object):
"""
[1]. The simple way with global configuration:
>>> cloner = ObjectCloner()
>>> cloner.set_objects = [obj1, obj2] # or can be queryset
>>> cloner.include_childs = True
>>> cloner.max_clones = 1
>>> cloner.execute()
[2]. Clone the objects with custom configuration per-each objects.
>>> cloner = ObjectCloner()
>>> cloner.set_objects = [
{
'object': obj1,
'include_childs': True,
'max_clones': 2
},
{
'object': obj2,
'include_childs': False,
'max_clones': 1
}
]
>>> cloner.execute()
"""
set_objects = [] # list/queryset of objects to clone.
include_childs = True # include all their childs or not.
max_clones = 1 # maximum clone per-objects.
def clone_object(self, object):
"""
function to clone the object.
:param `object` is an object to clone, e.g: <Post: object(1)>
:return new object.
"""
try:
object.pk = None
object.save()
return object
except IntegrityError:
return None
def clone_childs(self, object):
"""
function to clone all childs of current `object`.
:param `object` is a cloned parent object, e.g: <Post: object(1)>
:return
"""
# bypass the none object.
if object is None:
return
# find the related objects contains with this current object.
# e.g: (<ManyToOneRel: app.comment>,)
related_objects = object._meta.related_objects
if len(related_objects) > 0:
for relation in related_objects:
# find the related field name in the child object, e.g: 'post'
remote_field_name = relation.remote_field.name
# find all childs who have the same parent.
# e.g: childs = Comment.objects.filter(post=object)
childs = relation.related_model.objects.all()
for old_child in childs:
new_child = self.clone_object(old_child)
if new_child is not None:
# FIXME: When the child field as M2M field, we gote this error.
# "TypeError: Direct assignment to the forward side of a many-to-many set is prohibited. Use comments.set() instead."
# how can I clone that M2M values?
setattr(new_child, remote_field_name, object)
new_child.save()
self.clone_childs(new_child)
return
def execute(self):
include_childs = self.include_childs
max_clones = self.max_clones
new_objects = []
for old_object in self.set_objects:
# custom per-each objects by using dict {}.
if isinstance(old_object, dict):
include_childs = old_object.get('include_childs', True)
max_clones = old_object.get('max_clones', 1)
old_object = old_object.get('object') # assigned as object or None.
for _ in range(max_clones):
new_object = self.clone_object(old_object)
if new_object is not None:
if include_childs:
self.clone_childs(new_object)
new_objects.append(new_object)
return new_objects
但是，问题是当子字段作为 M2M 字段时，我们收到此错误。
>>> cloner.set_objects = [post]
>>> cloner.execute()
Traceback (most recent call last):
File "<console>", line 1, in <module>
File "/home/agus/envs/env-django-cloner/django-object-cloner/object_cloner_demo/app/utils.py", line 114, in execute
self.clone_childs(new_object)
File "/home/agus/envs/env-django-cloner/django-object-cloner/object_cloner_demo/app/utils.py", line 79, in clone_childs
self.clone_childs(new_child)
File "/home/agus/envs/env-django-cloner/django-object-cloner/object_cloner_demo/app/utils.py", line 76, in clone_childs
setattr(new_child, remote_field_name, object)
File "/home/agus/envs/env-django-cloner/lib/python3.7/site-packages/django/db/models/fields/related_descriptors.py", line 546, in __set__
% self._get_set_deprecation_msg_params(),
TypeError: Direct assignment to the forward side of a many-to-many set is prohibited. Use comments.set() instead.
>>>
错误来自setattr(...), and “改用comments.set()”，但我仍然困惑如何更新该 m2m 值？
new_child = self.clone_object(old_child)
if new_child is not None:
setattr(new_child, remote_field_name, object)
new_child.save()
我也尝试过下面的这段代码，但仍然有一个错误。克隆的 m2m 对象很多且未填充到 m2m 值中。
if new_child is not None:
# check the object_type
object_type = getattr(new_child, remote_field_name)
if hasattr(object_type, 'pk'):
# this mean is `object_type` as real object.
# so, we can directly use the `setattr(...)`
# to update the old relation value with new relation value.
setattr(new_child, remote_field_name, object)
elif hasattr(object_type, '_queryset_class'):
# this mean is `object_type` as m2m queryset (ManyRelatedManager).
# django.db.models.fields.related_descriptors.\
# create_forward_many_to_many_manager.<locals>.ManyRelatedManager
# check the old m2m values, and assign into new object.
# FIXME: IN THIS CASE STILL GOT AN ERROR
old_m2m_values = getattr(old_child, remote_field_name).all()
object_type.add(*old_m2m_values)
new_child.save()
