删除时的Django无止境循环

Question

也许以下是django的一个bug：

我有三个模型，其中一个有一个自定义的__init__方法：

from django.db import models


class Foo(models.Model):
    my_foo = models.CharField(max_length=1000)


class Bar(models.Model):
    bar1 = models.CharField(max_length=1000, default="")
    bar2 = models.BooleanField(default=False)
    foo = models.ForeignKey(Foo, on_delete=models.CASCADE)

    def __init__(self, *args, **kwargs):
        super(Bar, self).__init__(*args, **kwargs)
        print("check")
        self._original_bar1 = self.bar1
        self._original_bar2 = self.bar2


class Baz(models.Model):
    bar = models.ForeignKey(Bar, on_delete=models.CASCADE)

创建一个Foo对象和一个对应的Bar对象（通过管理界面）可以很好地工作。 然而，当我删除Foo对象时，这将导致__init__方法的无休止循环

如果我把模型稍微重写一下

from django.db import models


class Foo(models.Model):
    my_foo = models.CharField(max_length=1000)


class AbstractBar2(models.Model):
    bar2 = models.BooleanField(default=False)

    def __init__(self, *args, **kwargs):
        super(AbstractBar2, self).__init__(*args, **kwargs)
        print("check")
        self._original_bar2 = self.bar2

    class Meta:
        abstract = True


class AbstractBar1(models.Model):
    bar1 = models.CharField(max_length=1000, default="")

    def __init__(self, *args, **kwargs):
        super(AbstractBar1, self).__init__(*args, **kwargs)
        print("check")
        self._original_bar1 = self.bar1

    class Meta:
        abstract = True


class Bar(AbstractBar1, AbstractBar2):
    foo = models.ForeignKey(Foo, on_delete=models.CASCADE)


class Baz(models.Model):
    bar = models.ForeignKey(Bar, on_delete=models.CASCADE)

这是错误的

Fatal Python error: _Py_CheckRecursiveCall: Cannot recover from stack overflow.
Python runtime state: initialized

Current thread 0x000035d0 (most recent call first):
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\fields\__init__.py", line 807 in get_prep_value
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\fields\__init__.py", line 1770 in get_prep_value
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\lookups.py", line 76 in get_prep_lookup
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\lookups.py", line 24 in __init__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\sql\query.py", line 1165 in build_lookup
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\sql\query.py", line 1319 in build_filter
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\sql\query.py", line 1377 in _add_q
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\sql\query.py", line 1358 in add_q
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 969 in _filter_or_exclude_inplace
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 962 in _filter_or_exclude
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 942 in filter
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\manager.py", line 85 in manager_method
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\base.py", line 623 in refresh_from_db
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query_utils.py", line 149 in __get__
  File "C:\Users\name\PycharmProjects\djangoTest\foobar\models.py", line 26 in __init__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\base.py", line 513 in from_db
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 71 in __iter__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 1308 in _fetch_all
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 269 in __len__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 425 in get
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\base.py", line 635 in refresh_from_db
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query_utils.py", line 149 in __get__
  File "C:\Users\name\PycharmProjects\djangoTest\foobar\models.py", line 14 in __init__
  File "C:\Users\name\PycharmProjects\djangoTest\foobar\models.py", line 24 in __init__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\base.py", line 513 in from_db
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 71 in __iter__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 1308 in _fetch_all
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 269 in __len__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 425 in get
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\base.py", line 635 in refresh_from_db
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query_utils.py", line 149 in __get__
  File "C:\Users\name\PycharmProjects\djangoTest\foobar\models.py", line 26 in __init__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\base.py", line 513 in from_db
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 71 in __iter__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 1308 in _fetch_all
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 269 in __len__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 425 in get
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\base.py", line 635 in refresh_from_db
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query_utils.py", line 149 in __get__
  File "C:\Users\name\PycharmProjects\djangoTest\foobar\models.py", line 14 in __init__
  File "C:\Users\name\PycharmProjects\djangoTest\foobar\models.py", line 24 in __init__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\base.py", line 513 in from_db
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 71 in __iter__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 1308 in _fetch_all
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 269 in __len__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 425 in get
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\base.py", line 635 in refresh_from_db
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query_utils.py", line 149 in __get__
  File "C:\Users\name\PycharmProjects\djangoTest\foobar\models.py", line 26 in __init__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\base.py", line 513 in from_db
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 71 in __iter__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 1308 in _fetch_all
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 269 in __len__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 425 in get
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\base.py", line 635 in refresh_from_db
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query_utils.py", line 149 in __get__
  File "C:\Users\name\PycharmProjects\djangoTest\foobar\models.py", line 14 in __init__
  File "C:\Users\name\PycharmProjects\djangoTest\foobar\models.py", line 24 in __init__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\base.py", line 513 in from_db
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 71 in __iter__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 1308 in _fetch_all
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 269 in __len__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 425 in get
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\base.py", line 635 in refresh_from_db
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query_utils.py", line 149 in __get__
  File "C:\Users\name\PycharmProjects\djangoTest\foobar\models.py", line 26 in __init__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\base.py", line 513 in from_db
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 71 in __iter__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 1308 in _fetch_all
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 269 in __len__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 425 in get
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\base.py", line 635 in refresh_from_db
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query_utils.py", line 149 in __get__
  File "C:\Users\name\PycharmProjects\djangoTest\foobar\models.py", line 14 in __init__
  File "C:\Users\name\PycharmProjects\djangoTest\foobar\models.py", line 24 in __init__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\base.py", line 513 in from_db
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 71 in __iter__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 1308 in _fetch_all
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 269 in __len__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 425 in get
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\base.py", line 635 in refresh_from_db
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query_utils.py", line 149 in __get__
  File "C:\Users\name\PycharmProjects\djangoTest\foobar\models.py", line 26 in __init__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\base.py", line 513 in from_db
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 71 in __iter__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 1308 in _fetch_all
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 269 in __len__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 425 in get
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\base.py", line 635 in refresh_from_db
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query_utils.py", line 149 in __get__
  File "C:\Users\name\PycharmProjects\djangoTest\foobar\models.py", line 14 in __init__
  File "C:\Users\name\PycharmProjects\djangoTest\foobar\models.py", line 24 in __init__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\base.py", line 513 in from_db
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 71 in __iter__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 1308 in _fetch_all
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 269 in __len__
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query.py", line 425 in get
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\base.py", line 635 in refresh_from_db
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\db\models\query_utils.py", line 149 in __get__
  File "C:\Users\name\PycharmProjects\djangoTest\foobar\models.py", line 26 in __init__
  ...

Thread 0x00000a60 (most recent call first):
  File "C:\Users\name\AppData\Local\Programs\Python\Python39\lib\selectors.py", line 315 in _select
  File "C:\Users\name\AppData\Local\Programs\Python\Python39\lib\selectors.py", line 324 in select
  File "C:\Users\name\AppData\Local\Programs\Python\Python39\lib\socketserver.py", line 232 in serve_forever
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\core\servers\basehttp.py", line 216 in run
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\core\management\commands\runserver.py", line 139 in inner_run
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\utils\autoreload.py", line 53 in wrapper
  File "C:\Users\name\AppData\Local\Programs\Python\Python39\lib\threading.py", line 888 in run
  File "C:\Users\name\AppData\Local\Programs\Python\Python39\lib\threading.py", line 950 in _bootstrap_inner
  File "C:\Users\name\AppData\Local\Programs\Python\Python39\lib\threading.py", line 908 in _bootstrap

Thread 0x00000c7c (most recent call first):
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\utils\autoreload.py", line 374 in tick
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\utils\autoreload.py", line 324 in run_loop
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\utils\autoreload.py", line 318 in run
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\utils\autoreload.py", line 603 in start_django
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\utils\autoreload.py", line 618 in run_with_reloader
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\core\management\commands\runserver.py", line 103 in run
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\core\management\commands\runserver.py", line 96 in handle
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\core\management\base.py", line 371 in execute
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\core\management\commands\runserver.py", line 61 in execute
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\core\management\base.py", line 330 in run_from_argv
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\core\management\__init__.py", line 395 in execute
  File "C:\Users\name\PycharmProjects\global39\djangoTest\lib\site-packages\django\core\management\__init__.py", line 401 in execute_from_command_line
  File "C:\Users\name\PycharmProjects\djangoTest\manage.py", line 18 in main
  File "C:\Users\name\PycharmProjects\djangoTest\manage.py", line 22 in <module>

Process finished with exit code -1

有什么想法吗

Answer 1

这种行为已经向Django问题跟踪程序（#31435，#31475，#32660）报告过几次

建议使用Model.from_db()进行自定义模型加载，并且还有some documentation可用的方法。 如果这是不可能的，则使用self.__dict__.get('attribute')作为替代方法，在overrite __init__方法中调用

这在处理https://stackoverflow.com/a/1793323/2159075中建议的多个属性时尤其重要