为什么我看到TypeError：__ init __（）缺少1个必需的位置参数：＆＃39; on_delete＆＃39;即使我使用on_delete错误？

Question

我在django做一个课程，这是models.py代码：

from django.db import models
from django.contrib.auth.models import User

# Create your models here

class Game(models.Model):
    first_player = models.ForeignKey(User, related_name = "games_first_player")
    second_player = models.ForeignKey(User, related_name = "games_second_player")
    start_time = models.DateTimeField(auto_now_add=True)
    last_date = models.DateTimeField(auto_now=True)

class Move(models.Model):
    x = models.IntegerField()
    y = models.IntegerField()
    comment = models.CharField(max_length=300, blank=True)
    by_first_player = models.BooleanField()
    game = models.ForeignKey(Game, on_delete=models.CASCADE )

即使我使用on_delete关键字参数，我在运行makemigrations时看到以下错误消息：

(dev) D:\django\projects\tictactoe>python manage.py makemigrations
Traceback (most recent call last):   File "manage.py", line 15, in
<module>
    execute_from_command_line(sys.argv)   File "D:\django\projects\dev\lib\site-packages\django\core\management\__init__.py",
line 371, in execute_from_command_line
    utility.execute()   File "D:\django\projects\dev\lib\site-packages\django\core\management\__init__.py",
line 347, in execute
    django.setup()   File "D:\django\projects\dev\lib\site-packages\django\__init__.py", line
24, in setup
    apps.populate(settings.INSTALLED_APPS)   File "D:\django\projects\dev\lib\site-packages\django\apps\registry.py",
line 112, in populate
    app_config.import_models()   File "D:\django\projects\dev\lib\site-packages\django\apps\config.py", line
198, in import_models
    self.models_module = import_module(models_module_name)   File "D:\django\projects\dev\lib\importlib\__init__.py", line 126, in
import_module
    return _bootstrap._gcd_import(name[level:], package, level)   File "<frozen importlib._bootstrap>", line 994, in _gcd_import   File
"<frozen importlib._bootstrap>", line 971, in _find_and_load   File
"<frozen importlib._bootstrap>", line 955, in _find_and_load_unlocked 
File "<frozen importlib._bootstrap>", line 665, in _load_unlocked  
File "<frozen importlib._bootstrap_external>", line 678, in
exec_module   File "<frozen importlib._bootstrap>", line 219, in
_call_with_frames_removed   File "D:\django\projects\tictactoe\gameplay\models.py", line 6, in <module>
    class Game(models.Model):   File "D:\django\projects\tictactoe\gameplay\models.py", line 7, in Game
    first_player = models.ForeignKey(User, related_name = "games_first_player") TypeError: __init__() missing 1 required
positional argument: 'on_delete'

Answer 1

每次使用models.ForeignKey时，都应传递参数on_delete=models.CASCADE