问题：在执行python manage.py makemigrations learning_logs时，系统会报错，提示：TypeError: __init__() missing 1 required positional argument: 'on_delete'

(ll_env) c:\WorkSpace\SimpleTest\learning_log>python manage.py makemigrations learning_logs

Traceback (most recent call last):

  File "manage.py", line 15, in <module>

    execute_from_command_line(sys.argv)

  File "c:\WorkSpace\SimpleTest\learning_log\ll_env\lib\site-packages\django\core\management\__init__.py", line 371, in execute_from_command_line

    utility.execute()

  File "c:\WorkSpace\SimpleTest\learning_log\ll_env\lib\site-packages\django\core\management\__init__.py", line 347, in execute

    django.setup()

  File "c:\WorkSpace\SimpleTest\learning_log\ll_env\lib\site-packages\django\__init__.py", line 24, in setup

    apps.populate(settings.INSTALLED_APPS)

  File "c:\WorkSpace\SimpleTest\learning_log\ll_env\lib\site-packages\django\apps\registry.py", line 112, in populate

    app_config.import_models()

  File "c:\WorkSpace\SimpleTest\learning_log\ll_env\lib\site-packages\django\apps\config.py", line 198, in import_models

    self.models_module = import_module(models_module_name)

  File "C:\python36\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 "c:\WorkSpace\SimpleTest\learning_log\learning_logs\models.py", line 13, in <module>

    class Entry(models.Model):

  File "c:\WorkSpace\SimpleTest\learning_log\learning_logs\models.py", line 15, in Entry

    topic = models.ForeignKey(Topic)

TypeError: __init__() missing 1 required positional argument: 'on_delete'

 

 

 

 

 

 

 

 

 

 

 

 

 

 

代码如下：

from django.db import models

# Create your models here.

class Topic(models.Model):

    """用户学习的主题"""

    text = models.CharField(max_length=200)

    date_added = models.DateTimeField(auto_now_add=True)

   

    def __str__(self):

        """返回模型的字符串表示"""

        return self.text

class Entry(models.Model):

    """学到的有关某个主题的具体知识"""

    topic = models.ForeignKey(Topic)

    text = models.TextField()

    date_added = models.DateTimeField(auto_now_add=True)

   

    class Meta:

        verbose_name_plural = 'entries'

   

    def __str__(self):

        """返回模型的字符串表示"""

       

        return self.text[:50] + "..."

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

解决办法：修改指定外键的方式

from django.db import models

# Create your models here.

class Topic(models.Model):

    """用户学习的主题"""

    text = models.CharField(max_length=200)

    date_added = models.DateTimeField(auto_now_add=True)

   

    def __str__(self):

        """返回模型的字符串表示"""

        return self.text

class Entry(models.Model):

    """学到的有关某个主题的具体知识"""

    topic = models.ForeignKey(Topic, on_delete=models.CASCADE)

    text = models.TextField()

    date_added = models.DateTimeField(auto_now_add=True)

   

    class Meta:

        verbose_name_plural = 'entries'

   

    def __str__(self):

        """返回模型的字符串表示"""

       

        return self.text[:50] + "..."