Support Django 5.0

[aliceni81]

The current version is incompatible with Django 5.0.
There is no _get_flatchoices in django's CharField anymore, instead Django provides flatchoices directly. Therefore, the following code in db/fields.py should be removed.

def _get_flatchoices(self):
        flat_choices = super(MultiSelectField, self)._get_flatchoices()

        class MSFFlatchoices(list):
            # Used to trick django.contrib.admin.utils.display_for_field into
            # not treating the list of values as a dictionary key (which errors
            # out)
            def __bool__(self):
                return False
            __nonzero__ = __bool__
        return MSFFlatchoices(flat_choices)
flatchoices = property(_get_flatchoices)

[ssherchan08]

I was also wondering why my data was not being fetched. Spent hours debugging. Thanks for this! It helped me save so much time.

[symphoton]

In my application, simply removing those lines breaks the display in the admin view. I recommend keeping the code, but replacing

flat_choices = super(MultiSelectField, self)._get_flatchoices()

by

flat_choices = super(MultiSelectField, self).flatchoices

or

try:
    flat_choices = super(MultiSelectField, self).flatchoices
except AttributeError:
    flat_choices = super(MultiSelectField, self)._get_flatchoices()

for backwards compatibility

[sadra-allahyari]

Big thanks, everyone! I was struggling to figure out how to fix it.