IndexError with Django 4.1

[symphoton]

• Unfortunately this package breaks with Django 4.1.

The error message is as follows:

File "*****lib/python3.9/site-packages/multiselectfield/db/fields.py", line 72, in init
self.validators[0] = MaxValueMultiFieldValidator(self.max_length)
IndexError: list assignment index out of range

• Steps to reproduce:
  Use a MultiSelectField without explicitly specifying max_lenght attribute

• Reason for failure is the following django commit:
  django/django@0ed2919

Obviously, django team realized that always adding a MaxValueFieldValidator if max_lenght is omitted is not a good idea for derived classes (like MultiSelectField) and

• Proposed solution:

1. Append MaxValueMultiFieldValidator in case len(self.validators)==0.
2. Keep current logic if len(self.validators)>0 to stay compatible with older Django versions.

• Potential workaround for users:
  explicitly specify max_length in MultiSelectField, this should lead to old behaviour even with Django 4.1
  Drawback is that this disables the automatic max_length computation of this packages. Therefore be careful to choose max_lenght big enough

[hmpf]

This also holds for Django 4.0.

[mortenthansen]

I am seeing the same issue after an upgrade from django 4.0.7 to 4.1.2

Thanks for the workaround.

[megges2000]

• Potential workaround for users:
  explicitly specify max_length in MultiSelectField, this should lead to old behaviour even with Django 4.1
  Drawback is that this disables the automatic max_length computation of this packages. Therefore be careful to choose max_lenght big enough

Thanks for that.
I just use the get_max_length function for max_length, so the automatic max_length computation still works.

from multiselectfield.utils import get_max_length
from multiselectfield import MultiSelectField

class TestModel(models.Model):
    multifield = MultiSelectField(choices=MultiChoices.choices, blank=True, null=True, max_length=get_max_length(MultiChoices.choices, None))

[PraveenChordia]

Multi

• Potential workaround for users:
  explicitly specify max_length in MultiSelectField, this should lead to old behaviour even with Django 4.1
  Drawback is that this disables the automatic max_length computation of this packages. Therefore be careful to choose max_lenght big enough

Thanks for that. I just use the get_max_length function for max_length, so the automatic max_length computation still works.

from multiselectfield.utils import get_max_length
from multiselectfield import MultiSelectField

class TestModel(models.Model):
    multifield = MultiSelectField(choices=MultiChoices.choices, blank=True, null=True, max_length=get_max_length(MultiChoices.choices, None))

MultiChoices not defined.

[mikemanger]

@PraveenChordia Set choices to be a list of options. Usually you'd define a constant in the model class and reference it like so

from multiselectfield import MultiSelectField
from multiselectfield.utils import get_max_length


class TestModel(models.Model):
    MULTIFIELD_CHOICES = (
        ('read', 'Code'),
        ('you', 'Copy'),
    )
    multifield = MultiSelectField(
        choices=MULTIFIELD_CHOICES,
        max_length=get_max_length(MULTIFIELD_CHOICES, None),
    )

[violuke]

@goinnn thanks for the great package, but would it be possible to merge #132 so this can work on Django 4.0+?

[blag]

Django 4.1 support has already ended, but we still test against Django 4.2 and 5.0, and tests are passing. Closing, since I think we fixed this in #148 and elsewhere.