Question

我想迁移一些模型，但是具有外键功能的模型会引起一些问题。

我运行了以下代码，并导致了错误

python manage.py migrate

外键似乎是问题

class Webpage(models.Model):   
    topic =models.ForeignKey(Topic)
    name = models.CharField(max_length=264 , unique=True)
    url = models.URLField(unique=True)

    def __str__(self):
       return self.name

Traceback (most recent call last):
 File "C:\Users\helin\Anaconda3\envs\myenv\lib\sitepackages\django\utils\autoreload.py", line 225, in wrapper fn(*args, **kwargs)
 File "C:\Users\helin\Anaconda3\envs\myenv\lib\site-packages\django\core\management\commands\runserver.py", line 109, in inner_run
        autoreload.raise_last_exception()
 File "C:\Users\helin\Anaconda3\envs\myenv\lib\site-packages\django\utils\autoreload.py", line 248, in raise_last_exception
        raise _exception[1]
 File "C:\Users\helin\Anaconda3\envs\myenv\lib\site-packages\django\core\management\__init__.py", line 337, in execute autoreload.check_errors(django.setup)()
 File "C:\Users\helin\Anaconda3\envs\myenv\lib\sitepackages\django\utils\autoreload.py", line 225, in wrapper fn(*args, **kwargs)
 File "C:\Users\helin\Anaconda3\envs\myenv\lib\site-packages\django\__init__.py", line 24, in setup
        apps.populate(settings.INSTALLED_APPS)
 File "C:\Users\helin\Anaconda3\envs\myenv\lib\site-packages\django\apps\registry.py", line 112, in populate
        app_config.import_models()
 File "C:\Users\helin\Anaconda3\envs\myenv\lib\site-packages\django\apps\config.py", line 198, in import_models
        self.models_module = import_module(models_module_name)
 File "C:\Users\helin\Anaconda3\envs\myenv\lib\importlib\__init__.py", line 126, in import_module
        return _bootstrap._gcd_import(name[level:], package, level)
 File "<frozen importlib._bootstrap>", line 985, in _gcd_import
 File "<frozen importlib._bootstrap>", line 968, in _find_and_load
 File "<frozen importlib._bootstrap>", line 957, in _find_and_load_unlocked
 File "<frozen importlib._bootstrap>", line 673, in _load_unlocked
 File "<frozen importlib._bootstrap_external>", line 697, in exec_module
 File "<frozen importlib._bootstrap>", line 222, in _call_with_frames_removed
 File "C:\Users\helin\Downloads\my_django\first_project\first_app\models.py", line 12, in <module>
        class Webpage(models.Model):
 File "C:\Users\helin\Downloads\my_django\first_project\first_app\models.py", line 13, in Webpage
        topic =models.ForeignKey(Topic)
 TypeError: __init__() missing 1 required positional argument: 'on_delete'

Answer 1

是的，您缺少1个必需的位置参数：'on_delete'。

使用外键时，需要向其传递“ on_delete”参数。这样可以确保每当删除此外键为其主键的表/记录时，它将自动删除/保护用作外键的表的记录。

示例：

class Customer(models.Model):
    customer_id = <something>
class Account(models.Model):
    customer_id = models.ForeignKey(Customer, on_delete=models.CASCADE)

因此，当在与客户相关的表中删除具有customer_id = x的客户时，它将删除“帐户”表中的相应记录。

您可以阅读here

在models.py中添加外键时遇到错误

1 个答案: