Django 1.7 makemigrations - ValueError：无法序列化类

Question

我在从 Django 1.6.11 升级到 1.7 时遇到了一个有趣的问题。这似乎是基于我目前如何分割文件。目前，由于方法数量庞大，模型方法与模型存储在单独的文件中。

例如拆分如下：

help
|_ modelmethods
|  |_ __init__.py
|  |_ thread_methods.py
|_ __init__.py
|_ models.py

帮助应用文件夹中的__init__.py 如下所示：

""" __init__.py for help app."""

from help.modelmethods.thread_methods import *

thread_methods.py 看起来像这样：

"""Methods for the Thread model."""

from help.models import Thread

class ThreadMethods:

    """Adds methods on to the Thread model."""

    def do_the_thing(self):
        pass

Thread.__bases__ += (ThreadMethods,)

我看到的错误如下：

Migrations for 'help':
  0001_initial.py:
    - Create model Thread
Traceback (most recent call last):
  File "manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/Users/user/.virtualenvs/stuff/lib/python2.7/site-packages/django/core/management/__init__.py", line 385, in execute_from_command_line
    utility.execute()
  File "/Users/user/.virtualenvs/stuff/lib/python2.7/site-packages/django/core/management/__init__.py", line 377, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/Users/user/.virtualenvs/stuff/lib/python2.7/site-packages/django/core/management/base.py", line 288, in run_from_argv
    self.execute(*args, **options.__dict__)
  File "/Users/user/.virtualenvs/stuff/lib/python2.7/site-packages/django/core/management/base.py", line 338, in execute
    output = self.handle(*args, **options)
  File "/Users/user/.virtualenvs/stuff/lib/python2.7/site-packages/django/core/management/commands/makemigrations.py", line 124, in handle
    self.write_migration_files(changes)
  File "/Users/user/.virtualenvs/stuff/lib/python2.7/site-packages/django/core/management/commands/makemigrations.py", line 152, in write_migration_files
    migration_string = writer.as_string()
  File "/Users/user/.virtualenvs/stuff/lib/python2.7/site-packages/django/db/migrations/writer.py", line 129, in as_string
    operation_string, operation_imports = OperationWriter(operation).serialize()
  File "/Users/user/.virtualenvs/stuff/lib/python2.7/site-packages/django/db/migrations/writer.py", line 86, in serialize
    arg_string, arg_imports = MigrationWriter.serialize(arg_value)
  File "/Users/user/.virtualenvs/stuff/lib/python2.7/site-packages/django/db/migrations/writer.py", line 245, in serialize
    item_string, item_imports = cls.serialize(item)
  File "/Users/user/.virtualenvs/stuff/lib/python2.7/site-packages/django/db/migrations/writer.py", line 380, in serialize
    raise ValueError("Cannot serialize: %r\nThere are some values Django cannot serialize into migration files.\nFor more, see https://docs.djangoproject.com/en/dev/topics/migrations/#migration-serializing" % value)
ValueError: Cannot serialize: <class help.modelmethods.thread_methods.ThreadMethods at 0x1105c3870>
There are some values Django cannot serialize into migration files.
For more, see https://docs.djangoproject.com/en/dev/topics/migrations/#migration-serializing

我意识到它正在尝试序列化该类并使其窒息。有没有好的方法来解决这个问题并保持分离？或者，唯一可比较的方法是将models.py 文件分解为具有正确__init__.py 设置的模型文件夹，并且每个文件专用于一个模型，该模型还包含所有相关方法（以及确保没有循环导入介绍）。

Answer 1

由于自定义验证器，我无法迁移。我的问题是我没有正确阅读the manual，上面写着：

如果在验证器模型字段中使用基于类的验证器 选项，您应该确保它可以被迁移序列化 通过添加deconstruct() 和__eq__() 方法来构建框架。

哪个指向migrations-docs，它解释了为什么需要deconstruct() 和__eq__() 以及如何编写它们。

也应该适用于其他类，而不仅仅是验证器。

Answer 2

这可能由于多种原因而发生，在我的情况下，我将 default=User.pk 设置为 user 导致了问题。我的 django 版本是1.9

class Blog(models.Model):
    title = models.CharField(max_length=200)
    content = HTMLField()
    pub_date = models.DateTimeField('date published', auto_now_add=True)
    last_updated = models.DateTimeField('date published',default=timezone.now)
    user = models.ForeignKey(User, default=User.pk)#wrong
    user = models.ForeignKey(User, default=1)#correct, use any default value
    featured = models.ImageField(upload_to = 'featured', blank=True)

Answer 3

您需要从 object 类派生您的方法模型，还可以尝试从 ThreadMethods 派生 Thread 而不是将其添加到 __bases__。

class ThreadMethods(object):
    # ....