1.待创建的表信息
from django.db import models # Create your models here. class Book(models.Model): name=models.CharField(max_length=20) price=models.IntegerField() pub_date=models.DateField() publish=models.ForeignKey("Publish") def __str__(self): return self.name class Publish(models.Model): name=models.CharField(max_length=32) city=models.CharField(max_length=32) def __str__(self): return self.name
2.运行makemigrations报错
Traceback (most recent call last): File "manage.py", line 15, in <module> execute_from_command_line(sys.argv) File "/root/Django_env/ORM_mutil/venv/lib/python3.6/site-packages/django/core/management/__init__.py", line 371, in execute_from_command_line utility.execute() File "/root/Django_env/ORM_mutil/venv/lib/python3.6/site-packages/django/core/management/__init__.py", line 347, in execute django.setup() File "/root/Django_env/ORM_mutil/venv/lib/python3.6/site-packages/django/__init__.py", line 24, in setup apps.populate(settings.INSTALLED_APPS) File "/root/Django_env/ORM_mutil/venv/lib/python3.6/site-packages/django/apps/registry.py", line 112, in populate app_config.import_models() File "/root/Django_env/ORM_mutil/venv/lib/python3.6/site-packages/django/apps/config.py", line 198, in import_models self.models_module = import_module(models_module_name) File "/root/.pyenv/versions/3.6.5/lib/python3.6/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 "/root/Django_env/ORM_mutil/app01/models.py", line 4, in <module> class Book(models.Model): File "/root/Django_env/ORM_mutil/app01/models.py", line 8, in Book publish=models.ForeignKey("Publish") TypeError: __init__() missing 1 required positional argument: 'on_delete' (venv) [root@localhost ORM_mutil]# python manage.py makemigrations Traceback (most recent call last): File "manage.py", line 15, in <module> execute_from_command_line(sys.argv) File "/root/Django_env/ORM_mutil/venv/lib/python3.6/site-packages/django/core/management/__init__.py", line 371, in execute_from_command_line utility.execute() File "/root/Django_env/ORM_mutil/venv/lib/python3.6/site-packages/django/core/management/__init__.py", line 347, in execute django.setup() File "/root/Django_env/ORM_mutil/venv/lib/python3.6/site-packages/django/__init__.py", line 24, in setup apps.populate(settings.INSTALLED_APPS) File "/root/Django_env/ORM_mutil/venv/lib/python3.6/site-packages/django/apps/registry.py", line 112, in populate app_config.import_models() File "/root/Django_env/ORM_mutil/venv/lib/python3.6/site-packages/django/apps/config.py", line 198, in import_models self.models_module = import_module(models_module_name) File "/root/.pyenv/versions/3.6.5/lib/python3.6/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 "/root/Django_env/ORM_mutil/app01/models.py", line 4, in <module> class Book(models.Model): File "/root/Django_env/ORM_mutil/app01/models.py", line 8, in Book publish=models.ForeignKey("Publish") TypeError: __init__() missing 1 required positional argument: 'on_delete'
3.报错原因
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。
4.解决办法
将第八行的代码改为:
publish=models.ForeignKey("Publish",on_delete=models.CASCADE,)
即在外键值的后面加上 on_delete=models.CASCADE