Django 1 to Django 2 on_delete error

Question

I believe this workflow was created for a previous Django version. Now when I am trying to upgrade it I get an error to add on_delete. Here is what I have done but it is still n

Answer 1

There is a workaround for this.

If you have lots and lots of table which needs adding "on_delete" parameter where ever Foreign-key or One-to-One key is used.. then going through all the models to add on_delete parameter would be very hectic. You can perform monkey-patch of foreign key to achieve your goal.

add the below monkey patch file in your project settings folder:

monkey_patches.py

from django.db import models
from django.db.models import ForeignKey
from django.db import models
from django.db.models import ForeignKey, OneToOneRel
from django.db.models.fields.related_descriptors import ReverseOneToOneDescriptor, ForwardOneToOneDescriptor
from django.utils.translation import gettext_lazy as _


class ForeignKeyMonkeyPatch(ForeignKey):
    def __init__(self, to, on_delete=None, *args, **kwargs):
        super().__init__(to, on_delete, *args, **kwargs)


class OneToOneFieldMonkeyPatch(ForeignKeyMonkeyPatch):
    many_to_many = False
    many_to_one = False
    one_to_many = False
    one_to_one = True

    related_accessor_class = ReverseOneToOneDescriptor
    forward_related_accessor_class = ForwardOneToOneDescriptor
    rel_class = OneToOneRel

    description = _("One-to-one relationship")

    def __init__(self, to, on_delete=None, *args, **kwargs):
        kwargs['unique'] = True
        super().__init__(to, on_delete, *args, **kwargs)

    def deconstruct(self):
        name, path, args, kwargs = super().deconstruct()
        if "unique" in kwargs:
            del kwargs['unique']
        return name, path, args, kwargs

    def formfield(self, **kwargs):
        if self.remote_field.parent_link:
            return None
        return super().formfield(**kwargs)

    def save_form_data(self, instance, data):
        if isinstance(data, self.remote_field.model):
            setattr(instance, self.name, data)
        else:
            setattr(instance, self.attname, data)

    def _check_unique(self, **kwargs):
        # Override ForeignKey since check isn't applicable here.
        return []




setattr(models, 'ForeignKey', ForeignKeyMonkeyPatch)
setattr(models, 'OneToOneField', OneToOneFieldMonkeyPatch)

Now, call this file in your project settings...

from .monkey_patches import *

The above code will reset the ForeignKey and OneToOneField with our monkey-patched classes, thereby setting on_delete as None by default

P.S. (you can even create an app (named "monkey_patches" or anything that you desire..) and add the above code in models.py)

Answer 2

According to the Django 2.0 docs (and also the release notes) all Foreignkey fields now have a required on_delete parameter.

It seems to be missing on your model's fields. The release notes also advise to take a look at your migrations:

The on_delete argument for ForeignKey and OneToOneField is now required in models and migrations. Consider squashing migrations so that you have fewer of them to update.