django-south 与 django-audit-log

Question

我正在尝试对现有应用程序进行 django-south 迁移 以添加 django-audit-log 到它（跟踪用户发起的模块更改），但我遇到了重大错误。具体来说，action_user_id 字段是 LastUserField（它存储指定正在跟踪的更改的用户）。

如果我从一个空白模型开始，我可以通过以下方式添加一个audit_log：

from audit_log.models.managers import AuditLog
...
class SomeModel(models.Model)
    ...
    audit_log = AuditLog()

应用这个简单的更改并在 django-south 中进行模式迁移显然会给我一个错误：

 ! Cannot freeze field 'myapp.mymodelauditlogentry.action_user'
 ! (this field has class audit_log.models.fields.LastUserField)

 ! South cannot introspect some fields; this is probably because they are custom
 ! fields. If they worked in 0.6 or below, this is because we have removed the
 ! models parser (it often broke things).
 ! To fix this, read http://south.aeracode.org/wiki/MyFieldsDontWork

我阅读了 MyFieldsDontWork wiki （以及自定义字段/内省部分），但并不是 100% 清楚我需要做什么才能让这些字段发挥作用。

我尝试添加：

from south.modelsinspector import add_introspection_rules
add_introspection_rules([], ["^audit_log\.models\.fields\.LastUserField"])

到我的 models.py 中，这允许 ./manage.py schemamigration 创建迁移脚本，并且先前的错误消失。但是，当我尝试迁移（应用迁移）时，出现以下错误：

Running migrations for myapp:
 - Migrating forwards to 0004_auto__add_mymodelauditlogentry.
 > my_app:0004_auto__add_mymodelauditlogentry
Traceback (most recent call last):
  File "./manage.py", line 11, in <module>
    execute_manager(settings)
      File "/usr/local/lib/python2.6/dist-packages/Django-1.2.3-py2.6.egg/django/core/management/__init__.py", line 438, in execute_manager
    utility.execute()
  File "/usr/local/lib/python2.6/dist-packages/Django-1.2.3-py2.6.egg/django/core/management/__init__.py", line 379, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/usr/local/lib/python2.6/dist-packages/Django-1.2.3-py2.6.egg/django/core/management/base.py", line 191, in run_from_argv
    self.execute(*args, **options.__dict__)
  File "/usr/local/lib/python2.6/dist-packages/Django-1.2.3-py2.6.egg/django/core/management/base.py", line 220, in execute
    output = self.handle(*args, **options)
  File "/usr/local/lib/python2.6/dist-packages/South-0.7.3-py2.6.egg/south/management/commands/migrate.py", line 105, in handle
    ignore_ghosts = ignore_ghosts,
  File "/usr/local/lib/python2.6/dist-packages/South-0.7.3-py2.6.egg/south/migration/__init__.py", line 191, in migrate_app
    success = migrator.migrate_many(target, workplan, database)
  File "/usr/local/lib/python2.6/dist-packages/South-0.7.3-py2.6.egg/south/migration/migrators.py", line 221, in migrate_many
    result = migrator.__class__.migrate_many(migrator, target, migrations, database)
  File "/usr/local/lib/python2.6/dist-packages/South-0.7.3-py2.6.egg/south/migration/migrators.py", line 292, in migrate_many
    result = self.migrate(migration, database)
  File "/usr/local/lib/python2.6/dist-packages/South-0.7.3-py2.6.egg/south/migration/migrators.py", line 125, in migrate
    result = self.run(migration)
  File "/usr/local/lib/python2.6/dist-packages/South-0.7.3-py2.6.egg/south/migration/migrators.py", line 93, in run
    south.db.db.current_orm = self.orm(migration)
  File "/usr/local/lib/python2.6/dist-packages/South-0.7.3-py2.6.egg/south/migration/migrators.py", line 246, in orm
    return migration.orm()
  File "/usr/local/lib/python2.6/dist-packages/South-0.7.3-py2.6.egg/south/utils.py", line 62, in method
    value = function(self)
  File "/usr/local/lib/python2.6/dist-packages/South-0.7.3-py2.6.egg/south/migration/base.py", line 422, in orm
    return FakeORM(self.migration_class(), self.app_label())
  File "/usr/local/lib/python2.6/dist-packages/South-0.7.3-py2.6.egg/south/orm.py", line 46, in FakeORM
    _orm_cache[args] = _FakeORM(*args)  
  File "/usr/local/lib/python2.6/dist-packages/South-0.7.3-py2.6.egg/south/orm.py", line 125, in __init__
    self.models[name] = self.make_model(app_label, model_name, data)
  File "/usr/local/lib/python2.6/dist-packages/South-0.7.3-py2.6.egg/south/orm.py", line 318, in make_model
    field = self.eval_in_context(code, app, extra_imports)
  File "/usr/local/lib/python2.6/dist-packages/South-0.7.3-py2.6.egg/south/orm.py", line 236, in eval_in_context
    return eval(code, globals(), fake_locals)
  File "<string>", line 1, in <module>
  File "/usr/local/lib/python2.6/dist-packages/django_audit_log-0.2.1-py2.6.egg/audit_log/models/fields.py", line 12, in __init__
    super(LastUserField, self).__init__(User, null = True, **kwargs)
TypeError: __init__() got multiple values for keyword argument 'null'

编辑（中午 12/20）：如果我将这些行添加到 models.py 中，我可以应用 schemamigration，

from south.modelsinspector import add_introspection_rules, add_ignored_fields
add_ignored_fields(["^audit_log\.models\.fields\.LastUserField"])

除非audit_log 中间件不起作用，因为 myapp_mymodelauditlogentry 中没有通过“id”引用“auth_user”的 action_user_id 整数字段。然后我手动应用 SQL（sqlite 语法；通过在新创建的数据库上使用 sqliteman 获得。）

ALTER TABLE "myapp_mymodelauditlogentry" ADD "action_user_id" integer REFERENCES "auth_user" ("id");

并且它起作用了。如果有人解释我应该如何在 django-south 的上下文中通过迁移/内省来做到这一点，而不需要使用原始数据库依赖的 SQL，我仍然会给予赏金，并表示感激。

另外，我为 action_user_id 创建了索引。我注意到模型的正常创建会导致一个名为的索引

CREATE INDEX "myapp_mymodelauditlogentry_26679921" ON "myapp_mymodelauditlogentry" ("action_user_id")

，我发现哈希值 26679921 是根据 '%x' % (abs(hash(('action_user_id',))) 的字段名称创建的% 4294967296L,) 并且不基于任何其他内容（因此应始终为 _26679921，除非数据库要求截断长名称）。我不确定索引的名称是否重要；但想要安全。

Answer 1

最后是答案（和解释）。

向南迁移时，不仅会存储模型中的字段名称，还会存储传递给它的类型和参数。这样做的结果是 South 必须了解字段给出了哪些参数以及应该存储哪些参数。

因此，当您创建如下规则时：

add_introspection_rules([], ["^audit_log\.models\.fields\.LastUserField"])

Than South 将创建一个具有如下列的表：

(
  'action_user',
  self.gf('audit_log.models.fields.LastUserField')(
    related_name='_somemodel_audit_log_entry',
    null=True,
    to=orm['auth.User'],
  )
),

如您所见，其中包含一个 lated_name 参数、一个 null 参数和一个 to 参数。现在让我们看一下字段定义：

class LastUserField(models.ForeignKey):                                      
    """                                                                      
    A field that keeps the last user that saved an instance                  
    of a model. None will be the value for AnonymousUser.                    
    """                                                                      

    def __init__(self, **kwargs):                                            
        models.ForeignKey.__init__(self, User, null=True, **kwargs)          
        #print kwargs                                                        
        #super(LastUserField, self).__init__(User, null = True, **kwargs)    

    def contribute_to_class(self, cls, name):                                
        super(LastUserField, self).contribute_to_class(cls, name)            
        registry = registration.FieldRegistry(self.__class__)                
        registry.add_field(cls, self)                                        

我们在这里看到了什么？ ForeignKey 的第一个参数是 user（第一个参数是 to 属性）。第二个参数（也是硬编码的）是 null 参数。结果，在应用迁移时，South 和您的字段都会尝试设置这些参数。

然后你会得到错误：

TypeError: __init__() got multiple values for keyword argument 'null'

我们如何解决这个问题？

好吧，我们可以告诉 South，我们将这些参数作为默认值传递，以便它可以安全地忽略它们。

因此，我们创建了一组这样的规则：

rules = [(                                          
    (fields.LastUserField,),                        
    [],                                             
    {                                               
        'to': ['rel.to', {'default': User}],        
        'null': ['null', {'default': True}],        
    },                                              
)]   
add_introspection_rules(                           
    rules,                                         
    ['^audit_log\.models\.fields\.LastUserField'], 
)       

因此，South 现在了解如何存储参数以及哪些参数需要被忽略。所以新的字段定义将是这样的：

(
  'action_user',
  self.gf('audit_log.models.fields.LastUserField')(
    related_name='_somemodel_audit_log_entry'
  )
),

正如我们所看到的，lated_name 仍然在这里，但是 to 和 null 参数已经消失了。所以现在我们可以安全地应用迁移而不会发生冲突。

Answer 2

尽管使用了 @WoLpH 的答案中的步骤，我仍然无法创建迁移。我必须修改audit_log/models/fields.py 文件。我的 LastUserField 字段如下所示：

class LastUserField(models.ForeignKey):
    """ 
    A field that keeps the last user that saved an instance
    of a model. None will be the value for AnonymousUser.
    """

    def __init__(self, **kwargs):
        kwargs.pop('null', None)
        kwargs.pop('to', None)
        super(LastUserField, self).__init__(User, null = True, **kwargs)

    def contribute_to_class(self, cls, name):
        super(LastUserField, self).contribute_to_class(cls, name)
        registry = registration.FieldRegistry(self.__class__)
        registry.add_field(cls, self)

在我不得不采取此操作之前，以下内容已添加到我的 models.py 文件中（该文件不起作用）：

rules = [((fields.LastUserField,),
    [],    
    {   
        'to': ['rel.to', {'default': User}],
        'null': ['null', {'default': True}],
    },)]

# Add the rules for the `LastUserField`
add_introspection_rules(rules, ['^audit_log\.models\.fields\.LastUserField'])

关于我可以采取哪些措施来避免这种黑客行为的任何建议？