How to set ForeignKey on_delete in EXTRA_MODEL_FIELDS setting?

[tym-xqo]

Hello,

I am hoping someone can help me with this, as I am trying to upgrade an existing Mezz 4.3.1 (with a Cartridge shop included) to 6.0.0. In older version, we were using 'model injection' feature to add a ForeignKey field to cartridge.shop.models.CartItem and cartridge.shop.models.OrderItem each linked to an object members.Student in a separate custom application. This worked fine with earlier versions but now I'm getting an error because of course newer versions of Django require an on_delete argument.

My EXTRA_MODEL_FIELDS setting looks like:

EXTRA_MODEL_FIELDS = (
    (
        "cartridge.shop.models.CartItem.student",
        "ForeignKey",
        ("members.Student",),
        {"null": True},
    ),
    (
        "cartridge.shop.models.OrderItem.student",
        "ForeignKey",
        ("members.Student",),
        {"null": True},
    ),
)

When I try to makemigrations with these settings of course I get error

  File "/Users/thomas/projects/xxxxx/.venv/lib/python3.11/site-packages/mezzanine/boot/__init__.py", line 69, in parse_extra_model_fields
    raise ImproperlyConfigured(
django.core.exceptions.ImproperlyConfigured: The EXTRA_MODEL_FIELDS setting contains arguments for the field 'ForeignKey' which could not be applied: ForeignKey.__init__() missing 1 required positional argument: 'on_delete'

I have tried adding "on_delete=django.db.models.CASCADE" as a second argument in the third line of each field block, after members.Student but then get a different error:

django.core.exceptions.ImproperlyConfigured: The EXTRA_MODEL_FIELDS setting contains arguments for the field 'ForeignKey' which could not be applied: on_delete must be callable.

Is there a way I can get this work, please? Urgent reply here would be helpful, I am under a tight deadline to finish the upgrade.

[tym-xqo]

OK actually I got it, and was misunderstanding the structure of the EXTRA_MODEL_FIELDS sequences. Keyword arguments like on_delete are expected in the final dictionary portion of the field, where I already had "null": True, not in the tuple before with members.Student. So the working code was like:

EXTRA_MODEL_FIELDS = (
    (
        "cartridge.shop.models.CartItem.student",
        "ForeignKey",
        ("members.Student",),
        {"null": True, "on_delete": models.CASCADE},
    ),
    (
        "cartridge.shop.models.OrderItem.student",
        "ForeignKey",
        ("members.Student",),
        {"null": True, "on_delete": models.CASCADE},
    ),
)

(I also imported django.db.models at the top of my settings.py, but not sure that was necessary.)

Just thought I'd mention it in case anyone else has similar problem. Since the answer is not really the issue with upgrade that I thought it was, I'd prefer to simply the delete the whole question, but that doesn't seem to be an option here. Sorry for any confusion.