id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
26807	Document how to replicate SubfieldBase behavior of calling to_python on assignment	Aarni Koskela	nobody	"With the deprecation of `SubfieldBase`, custom fields no longer automatically have the `Creator` class behavior that calls `to_python()` on every assignment (see https://github.com/django/django/blob/4fd264b6f1737b0317fdd95b3d7ff3bba15ae6c3/django/db/models/fields/subclassing.py#L44), incl. construction.

This causes the problem described here – https://github.com/hzdg/django-enumfields/issues/60 – i.e. `enumfields.EnumField` doesn't coerce values to the actual `Enum` value types anymore.

The fix is naturally to reimplement a descriptor like `Creator` (and that does indeed fix this particular issue), but I feel like I'm missing something doing that.

(The deprecation warning for SubfieldBase says that one should use `from_db_value()`, but it doesn't get called on instance construction either, it seems.)

Here's a trivial py.test style test case (the assertions fail):

{{{
from django.db import models

class CoolCharField(models.CharField):
    def to_python(self, value):
        return str(value).upper() + ""!!!""

    def from_db_value(self, value):
        return self.to_python(value)


class CoolModel(models.Model):
    yay = CoolCharField()


def test_cool_char_field_1():
    m = CoolModel(yay=""ponies"")
    assert m.yay == ""PONIES!!!""


def test_cool_char_field_2():
    m = CoolModel()
    m.yay = ""ponies""
    assert m.yay == ""PONIES!!!""
}}}
"	Cleanup/optimization	closed	Documentation	1.8	Normal	fixed			Accepted	1	0	0	0	0	0