TypeError: __init__() missing 1 required positional argument: 'on_delete'
源代码:
from django.db import models # Create your models here. class Topic(models.Model): '''用户学习主题''' text=models.CharField(max_length=200) date_added=models.DateField(auto_now_add=True) def __str__(self): '''返回模型的字符串表示''' return self.text class Entry(models.Model): '''学到的有某个主题的具体知识''' #django 2.0后在django2.0后,定义外键和一对一关系的时候需要加on_delete选项,此参数为了避免两个表里的数据不一致问题,不然会报错 topic=models.ForeignKey(Topic) text=models.TextField() data_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]+"..."
错误:
(venv) D:\software\pythonWork\pythonWeb1>python manage.py makemigrations mysite Traceback (most recent call last): File "manage.py", line 15, in <module> execute_from_command_line(sys.argv) File "D:\software\pythonWork\pythonWeb1\venv\lib\site-packages\django\core\management\__init__.py", line 381, in execute_from_command_line utility.execute() File "D:\software\pythonWork\pythonWeb1\venv\lib\site-packages\django\core\management\__init__.py", line 357, in execute django.setup() File "D:\software\pythonWork\pythonWeb1\venv\lib\site-packages\django\__init__.py", line 24, in setup apps.populate(settings.INSTALLED_APPS) File "D:\software\pythonWork\pythonWeb1\venv\lib\site-packages\django\apps\registry.py", line 112, in populate app_config.import_models() File "D:\software\pythonWork\pythonWeb1\venv\lib\site-packages\django\apps\config.py", line 198, in import_models self.models_module = import_module(models_module_name) File "D:\software\pythonWork\pythonWeb1\venv\lib\importlib\__init__.py", line 126, in import_module return _bootstrap._gcd_import(name[level:], package, level) File "<frozen importlib._bootstrap>", line 986, in _gcd_import File "<frozen importlib._bootstrap>", line 969, in _find_and_load File "<frozen importlib._bootstrap>", line 958, in _find_and_load_unlocked File "<frozen importlib._bootstrap>", line 673, in _load_unlocked File "<frozen importlib._bootstrap_external>", line 665, in exec_module File "<frozen importlib._bootstrap>", line 222, in _call_with_frames_removed File "D:\software\pythonWork\pythonWeb1\mysite\models.py", line 13, in <module> class Entry(models.Model): File "D:\software\pythonWork\pythonWeb1\mysite\models.py", line 15, in Entry topic=models.ForeignKey(Topic) TypeError: __init__() missing 1 required positional argument: 'on_delete'
解决方法:
修改为如下:
topic=models.ForeignKey(Topic,on_delete=models.CASCADE)
问题原因:
- 在django2.0后,定义外键和一对一关系的时候需要加on_delete选项,此参数为了避免两个表里的数据不一致问题,不然会报错:
- TypeError: __init__() missing 1 required positional argument: 'on_delete'
- 举例说明:
- user=models.OneToOneField(User)
- owner=models.ForeignKey(UserProfile)
- 需要改成:
- user=models.OneToOneField(User,on_delete=models.CASCADE) --在老版本这个参数(models.CASCADE)是默认值
- owner=models.ForeignKey(UserProfile,on_delete=models.CASCADE) --在老版本这个参数(models.CASCADE)是默认值
- 参数说明:
- on_delete有CASCADE、PROTECT、SET_NULL、SET_DEFAULT、SET()五个可选择的值
- CASCADE:此值设置,是级联删除。
- PROTECT:此值设置,是会报完整性错误。
- SET_NULL:此值设置,会把外键设置为null,前提是允许为null。
- SET_DEFAULT:此值设置,会把设置为外键的默认值。
- SET():此值设置,会调用外面的值,可以是一个函数。
- 一般情况下使用CASCADE就可以了。