Getting TypeError: __init__() missing 1 required positional argument: 'on_delete' when trying to add parent table after child table with entries
I have two classes in my sqlite database, a parent table named Categorie
and the child table called Article
. I created first the child table class and addes entries. So first I had this:
class Article(models.Model):
titre=models.CharField(max_length=100)
auteur=models.CharField(max_length=42)
contenu=models.TextField(null=True)
date=models.DateTimeField(
auto_now_add=True,
auto_now=False,
verbose_name="Date de parution"
)
def __str__(self):
return self.titre
And after I have added parent table, and now my models.py
looks like this:
from django.db import models
# Create your models here.
class Categorie(models.Model):
nom = models.CharField(max_length=30)
def __str__(self):
return self.nom
class Article(models.Model):
titre=models.CharField(max_length=100)
auteur=models.CharField(max_length=42)
contenu=models.TextField(null=True)
date=models.DateTimeField(
auto_now_add=True,
auto_now=False,
verbose_name="Date de parution"
)
categorie = models.ForeignKey('Categorie')
def __str__(self):
return self.titre
So when I run python manage.py makemigrations <my_app_name>
, I get this error:
Traceback (most recent call last):
File "manage.py", line 15, in <module>
execute_from_command_line(sys.argv)
File "C:\Users\lislis\AppData\Local\Programs\Python\Python35-32\lib\site-packages\django-2.0-py3.5.egg\django\core\management\__init__.py", line 354, in execute_from_command_line
utility.execute()
File "C:\Users\lislis\AppData\Local\Programs\Python\Python35-32\lib\site-packages\django-2.0-py3.5.egg\django\core\management\__init__.py", line 330, in execute
django.setup()
File "C:\Users\lislis\AppData\Local\Programs\Python\Python35-32\lib\site-packages\django-2.0-py3.5.egg\django\__init__.py", line 24, in setup
apps.populate(settings.INSTALLED_APPS)
File "C:\Users\lislis\AppData\Local\Programs\Python\Python35-32\lib\site-packages\django-2.0-py3.5.egg\django\apps\registry.py", line 112, in populate
app_config.import_models()
File "C:\Users\lislis\AppData\Local\Programs\Python\Python35-32\lib\site-packages\django-2.0-py3.5.egg\django\apps\config.py", line 198, in import_models
self.models_module = import_module(models_module_name)
File "C:\Users\lislis\AppData\Local\Programs\Python\Python35-32\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 "C:\Users\lislis\Django\mon_site\blog\models.py", line 6, in <module>
class Article(models.Model):
File "C:\Users\lislis\Django\mon_site\blog\models.py", line 16, in Article
categorie = models.ForeignKey('Categorie')
TypeError: __init__() missing 1 required positional argument: 'on_delete'
I've seen some similar issues in stackoverflow, but it seems to not be the same problem: __init__() missing 1 required positional argument: 'quantity'
You can change the property categorie
of the class Article
like this:
categorie = models.ForeignKey(
'Categorie',
on_delete=models.CASCADE,
)
and the error should disappear.
Eventually you might need another option for on_delete
, check the documentation for more details:
https://docs.djangoproject.com/en/1.11/ref/models/fields/#django.db.models.ForeignKey
EDIT:
As you stated in your comment, that you don't have any special requirements for on_delete
, you could use the option DO_NOTHING
:
# ...
on_delete=models.DO_NOTHING,
# ...
Since Django 2.x, on_delete
is required.
Django Documentation
Deprecated since version 1.9: on_delete will become a required argument in Django 2.0. In older versions it defaults to CASCADE.
Since Django 2.0 the ForeignKey field requires two positional arguments:
- the model to map to
- the on_delete argument
categorie = models.ForeignKey('Categorie', on_delete=models.PROTECT)
Here are some methods can used in on_delete
- CASCADE
Cascade deletes. Django emulates the behavior of the SQL constraint ON DELETE CASCADE and also deletes the object containing the ForeignKey
- PROTECT
Prevent deletion of the referenced object by raising ProtectedError, a subclass of django.db.IntegrityError.
- DO_NOTHING
Take no action. If your database backend enforces referential integrity, this will cause an IntegrityError unless you manually add an SQL ON DELETE constraint to the database field.
you can find more about on_delete by reading the documentation.