尽管存在对象，但“NoneType”对象没有属性“seventh_five”

Question

我正在创建一个用户可以创建项目的网站。每个项目有 10 个宏观问题。每个宏观问题都有子问题。

我正在尝试检索宏观问题的答案。

projects_id包含我数据库中的所有项目。

  projects = Project.objects.all()

  projects_id = []

  for project in projects:

    projects_id.append(project.id)

所以我做了一个for循环：

  for project_id in projects_id:

    seventh_question_project = Seventhquestion.objects.all().filter(project=project_id).first()

    answer_seventh_five = seventh_question_project.seventh_five

        if answer_seventh_five == "No":

           unaudited_projects.append(answer_seventh_five)

        else:

           audited_projects.append(answer_seventh_five)

如果我使用控制台，我可以检索answer_seventh_five：

但是，如果加载页面，我会得到：

“NoneType”对象没有属性“seventh_five”

由于存在，我无法解释answer_seventh_five（因为我通过控制台检索它来测试它）

可能原因是我正在过滤而不是使用get.

我试过：

seventh_question_project = Seventhquestion.objects.get(project=project_id)

但我得到：

第七题匹配查询不存在。

但是： seventh_question_project = Seventhquestion.objects.all()有效

Answer 1

不要通过ID。这不是 Django ORM 的用途。只需循环浏览项目本身：for project in Project.objects.all():&nbsp; &nbsp; seventh_question_project = Seventhquestion.objects.all().filter(project=project).first()&nbsp; # <-- not project_id!&nbsp; &nbsp; # or better:&nbsp; &nbsp; # seventh_question_project = project.seventhquestion_set.first()&nbsp;&nbsp;&nbsp; &nbsp; if seventh_question_project:&nbsp; &nbsp; &nbsp; &nbsp; # you should always check, because you need to write fool-proof code&nbsp; &nbsp; &nbsp; &nbsp; answer_seventh_five = seventh_question_project.seventh_five&nbsp; &nbsp; &nbsp; &nbsp; ...但是通过关系，您可以更轻松地获取相关对象。因此，假设模型上的project字段是 a ，则相反的关系是：OneToOneFieldSeventhquestionseventhquestionfor project in Project.objects.all():&nbsp; &nbsp; if hasattr(project, "seventhquestion"):&nbsp; &nbsp; &nbsp; &nbsp; # still need to check, you never know&nbsp; &nbsp; &nbsp; &nbsp; answer_seventh_five = project.seventhquestion.seventh_five&nbsp; &nbsp; &nbsp; &nbsp; ...

Answer 2

这个怎么样？seventh_question_project = Seventhquestion.objects.filter(project=project_id).first()answer_seventh_five = seventh_question_project.seventh_five