模型在数据迁移期间不可用

Question

我在我的应用中添加了一个Target模型，该模型通过一对一字段标记Revision对象（从django-reversion）。标签取决于版本集中的对象，如果这些对象中的任何一个需要标签，则应该为整个版本设置标签。我试图使用django-south数据迁移遍历数据库中所有的Revision对象，检查关联的version_set中的每个对象，并在必要时设置标记。

class Migration(DataMigration): 

    def forwards(self, orm): 
     for revision in orm["reversion.Revision"].objects.all(): 
      try: 
       revision.target # the revision is already tagged 
      except: # revision.target raises different sorts of DoesNotExist errors, 
        # and I can't work out how to catch all of them 
       for version in revision.version_set.all(): 
        try: 
         tag = version.object.get_tag() # all models in my app that 
         orm.Target.objects.create( # specify tags have this method 
           revision=revision, 
           tag=tag) 
         break 
        except AttributeError: # the version set doesn't contain any 
         pass    # models that specify a tag 

的给出了一个错误：

[... lots of stuff cut ...], line 21, in forwards 
    for version in revision.version_set.all(): 
AttributeError: 'Revision' object has no attribute 'version_set' 

我怎样才能在不同的应用程序一个datamigration期间获得访问Revision对象version_set？

编辑感谢丹尼尔我进一步。在下面的代码我尝试通过访问所有车型迁移自己的orm：

def forwards(self, orm): 
    my_models = { # models with a .get_tag() method 
      "modela": orm.ModelA, 
      "modelb": orm.ModelB, 
      } 
    for revision in orm["reversion.Revision"].objects.all(): 
     for version in orm["reversion.Version"].objects.filter(revision=revision): 
      try: 
       model = my_models[version.content_type.model] 
       instance = model.objects.get(id=version.object_id) 
       tag = instance.get_tag() 
       orm.RevisionTargetLanguage.objects.create(
         revision=revision, 
         tag=tag) 
       break 
      except KeyError: # not one of the models with a .get_tag() method 
       pass 

这种失败在与例外DoesNotExist: ModelB matching query does not exist行instance = model.objects.get(id=version.object_id_int)。

Answer 1

你可以尝试

orm['reversion.Version'].objects.filter(revision=revision)